1NMAP(1) Nmap Reference Guide NMAP(1)
2
6 nmap - Network exploration tool and security / port scanner
7
9 nmap [Scan Type...] [Options] {target specification}
10
12 Nmap (“Network Mapper”) is an open source tool for network exploration
13 and security auditing. It was designed to rapidly scan large networks,
14 although it works fine against single hosts. Nmap uses raw IP packets
15 in novel ways to determine what hosts are available on the network,
16 what services (application name and version) those hosts are offering,
17 what operating systems (and OS versions) they are running, what type of
18 packet filters/firewalls are in use, and dozens of other
19 characteristics. While Nmap is commonly used for security audits, many
20 systems and network administrators find it useful for routine tasks
21 such as network inventory, managing service upgrade schedules, and
22 monitoring host or service uptime.
23 The output from Nmap is a list of scanned targets, with supplemental
25 information on each depending on the options used. Key among that
26 information is the “interesting ports table”. That table lists the
27 port number and protocol, service name, and state. The state is either
28 open, filtered, closed, or unfiltered. Open means that an application
29 on the target machine is listening for connections/packets on that
30 port. Filtered means that a firewall, filter, or other network
31 obstacle is blocking the port so that Nmap cannot tell whether it is
32 open or closed. Closed ports have no application listening on them,
33 though they could open up at any time. Ports are classified as
34 unfiltered when they are responsive to Nmap's probes, but Nmap cannot
35 determine whether they are open or closed. Nmap reports the state
36 combinations open|filtered and closed|filtered when it cannot determine
37 which of the two states describe a port. The port table may also
38 include software version details when version detection has been
39 requested. When an IP protocol scan is requested (-sO), Nmap provides
40 information on supported IP protocols rather than listening ports.
41 In addition to the interesting ports table, Nmap can provide further
43 information on targets, including reverse DNS names, operating system
44 guesses, device types, and MAC addresses.
45 A typical Nmap scan is shown in Example 1. The only Nmap arguments used
47 in this example are -A, to enable OS and version detection, script
48 scanning, and traceroute; -T4 for faster execution; and then the
49 hostname.
50 Example 1. A representative Nmap scan
52 # nmap -A -T4 scanme.nmap.org
54 Nmap scan report for scanme.nmap.org (74.207.244.221)
56 Host is up (0.029s latency).
57 rDNS record for 74.207.244.221: li86-221.members.linode.com
58 Not shown: 995 closed ports
59 PORT STATE SERVICE VERSION
60 22/tcp open ssh OpenSSH 5.3p1 Debian 3ubuntu7 (protocol 2.0)
61 | ssh-hostkey: 1024 8d:60:f1:7c:ca:b7:3d:0a:d6:67:54:9d:69:d9:b9:dd (DSA)
62 |_2048 79:f8:09:ac:d4:e2:32:42:10:49:d3:bd:20:82:85:ec (RSA)
63 80/tcp open http Apache httpd 2.2.14 ((Ubuntu))
64 |_http-title: Go ahead and ScanMe!
65 646/tcp filtered ldp
66 1720/tcp filtered H.323/Q.931
67 9929/tcp open nping-echo Nping echo
68 Device type: general purpose
69 Running: Linux 2.6.X
70 OS CPE: cpe:/o:linux:linux_kernel:2.6.39
71 OS details: Linux 2.6.39
72 Network Distance: 11 hops
73 Service Info: OS: Linux; CPE: cpe:/o:linux:kernel
74 TRACEROUTE (using port 53/tcp)
76 HOP RTT ADDRESS
77 [Cut first 10 hops for brevity]
78 11 17.65 ms li86-221.members.linode.com (74.207.244.221)
79 Nmap done: 1 IP address (1 host up) scanned in 14.40 seconds
81 The newest version of Nmap can be obtained from https://nmap.org. The
83 newest version of this man page is available at
84 https://nmap.org/book/man.html. It is also included as a chapter of
85 Nmap Network Scanning: The Official Nmap Project Guide to Network
86 Discovery and Security Scanning (see https://nmap.org/book/).
87
89 This options summary is printed when Nmap is run with no arguments, and
90 the latest version is always available at
91 https://svn.nmap.org/nmap/docs/nmap.usage.txt. It helps people remember
92 the most common options, but is no substitute for the in-depth
93 documentation in the rest of this manual. Some obscure options aren't
94 even included here.
95 Nmap 7.70SVN ( https://nmap.org )
97 Usage: nmap [Scan Type(s)] [Options] {target specification}
98 TARGET SPECIFICATION:
99 Can pass hostnames, IP addresses, networks, etc.
100 Ex: scanme.nmap.org, 192.168.0.1; 10.0.0-255.1-254
101 -iL <inputfilename>: Input from list of hosts/networks
102 -iR <num hosts>: Choose random targets
103 --exclude <host1[,host2][,host3],...>: Exclude hosts/networks
104 --excludefile <exclude_file>: Exclude list from file
105 HOST DISCOVERY:
106 -sL: List Scan - simply list targets to scan
107 -sn: Ping Scan - disable port scan
108 -Pn: Treat all hosts as online -- skip host discovery
109 -PS/PA/PU/PY[portlist]: TCP SYN/ACK, UDP or SCTP discovery to given ports
110 -PE/PP/PM: ICMP echo, timestamp, and netmask request discovery probes
111 -PO[protocol list]: IP Protocol Ping
112 -n/-R: Never do DNS resolution/Always resolve [default: sometimes]
113 --dns-servers <serv1[,serv2],...>: Specify custom DNS servers
114 --system-dns: Use OS's DNS resolver
115 --traceroute: Trace hop path to each host
116 SCAN TECHNIQUES:
117 -sS/sT/sA/sW/sM: TCP SYN/Connect()/ACK/Window/Maimon scans
118 -sU: UDP Scan
119 -sN/sF/sX: TCP Null, FIN, and Xmas scans
120 --scanflags <flags>: Customize TCP scan flags
121 -sI <zombie host[:probeport]>: Idle scan
122 -sY/sZ: SCTP INIT/COOKIE-ECHO scans
123 -sO: IP protocol scan
124 -b <FTP relay host>: FTP bounce scan
125 PORT SPECIFICATION AND SCAN ORDER:
126 -p <port ranges>: Only scan specified ports
127 Ex: -p22; -p1-65535; -p U:53,111,137,T:21-25,80,139,8080,S:9
128 --exclude-ports <port ranges>: Exclude the specified ports from scanning
129 -F: Fast mode - Scan fewer ports than the default scan
130 -r: Scan ports consecutively - don't randomize
131 --top-ports <number>: Scan <number> most common ports
132 --port-ratio <ratio>: Scan ports more common than <ratio>
133 SERVICE/VERSION DETECTION:
134 -sV: Probe open ports to determine service/version info
135 --version-intensity <level>: Set from 0 (light) to 9 (try all probes)
136 --version-light: Limit to most likely probes (intensity 2)
137 --version-all: Try every single probe (intensity 9)
138 --version-trace: Show detailed version scan activity (for debugging)
139 SCRIPT SCAN:
140 -sC: equivalent to --script=default
141 --script=<Lua scripts>: <Lua scripts> is a comma separated list of
142 directories, script-files or script-categories
143 --script-args=<n1=v1,[n2=v2,...]>: provide arguments to scripts
144 --script-args-file=filename: provide NSE script args in a file
145 --script-trace: Show all data sent and received
146 --script-updatedb: Update the script database.
147 --script-help=<Lua scripts>: Show help about scripts.
148 <Lua scripts> is a comma-separated list of script-files or
149 script-categories.
150 OS DETECTION:
151 -O: Enable OS detection
152 --osscan-limit: Limit OS detection to promising targets
153 --osscan-guess: Guess OS more aggressively
154 TIMING AND PERFORMANCE:
155 Options which take <time> are in seconds, or append 'ms' (milliseconds),
156 's' (seconds), 'm' (minutes), or 'h' (hours) to the value (e.g. 30m).
157 -T<0-5>: Set timing template (higher is faster)
158 --min-hostgroup/max-hostgroup <size>: Parallel host scan group sizes
159 --min-parallelism/max-parallelism <numprobes>: Probe parallelization
160 --min-rtt-timeout/max-rtt-timeout/initial-rtt-timeout <time>: Specifies
161 probe round trip time.
162 --max-retries <tries>: Caps number of port scan probe retransmissions.
163 --host-timeout <time>: Give up on target after this long
164 --scan-delay/--max-scan-delay <time>: Adjust delay between probes
165 --min-rate <number>: Send packets no slower than <number> per second
166 --max-rate <number>: Send packets no faster than <number> per second
167 FIREWALL/IDS EVASION AND SPOOFING:
168 -f; --mtu <val>: fragment packets (optionally w/given MTU)
169 -D <decoy1,decoy2[,ME],...>: Cloak a scan with decoys
170 -S <IP_Address>: Spoof source address
171 -e <iface>: Use specified interface
172 -g/--source-port <portnum>: Use given port number
173 --proxies <url1,[url2],...>: Relay connections through HTTP/SOCKS4 proxies
174 --data <hex string>: Append a custom payload to sent packets
175 --data-string <string>: Append a custom ASCII string to sent packets
176 --data-length <num>: Append random data to sent packets
177 --ip-options <options>: Send packets with specified ip options
178 --ttl <val>: Set IP time-to-live field
179 --spoof-mac <mac address/prefix/vendor name>: Spoof your MAC address
180 --badsum: Send packets with a bogus TCP/UDP/SCTP checksum
181 OUTPUT:
182 -oN/-oX/-oS/-oG <file>: Output scan in normal, XML, s|<rIpt kIddi3,
183 and Grepable format, respectively, to the given filename.
184 -oA <basename>: Output in the three major formats at once
185 -v: Increase verbosity level (use -vv or more for greater effect)
186 -d: Increase debugging level (use -dd or more for greater effect)
187 --reason: Display the reason a port is in a particular state
188 --open: Only show open (or possibly open) ports
189 --packet-trace: Show all packets sent and received
190 --iflist: Print host interfaces and routes (for debugging)
191 --append-output: Append to rather than clobber specified output files
192 --resume <filename>: Resume an aborted scan
193 --stylesheet <path/URL>: XSL stylesheet to transform XML output to HTML
194 --webxml: Reference stylesheet from Nmap.Org for more portable XML
195 --no-stylesheet: Prevent associating of XSL stylesheet w/XML output
196 MISC:
197 -6: Enable IPv6 scanning
198 -A: Enable OS detection, version detection, script scanning, and traceroute
199 --datadir <dirname>: Specify custom Nmap data file location
200 --send-eth/--send-ip: Send using raw ethernet frames or IP packets
201 --privileged: Assume that the user is fully privileged
202 --unprivileged: Assume the user lacks raw socket privileges
203 -V: Print version number
204 -h: Print this help summary page.
205 EXAMPLES:
206 nmap -v -A scanme.nmap.org
207 nmap -v -sn 192.168.0.0/16 10.0.0.0/8
208 nmap -v -iR 10000 -Pn -p 80
209 SEE THE MAN PAGE (https://nmap.org/book/man.html) FOR MORE OPTIONS AND EXAMPLES
210
212 Everything on the Nmap command-line that isn't an option (or option
213 argument) is treated as a target host specification. The simplest case
214 is to specify a target IP address or hostname for scanning.
215 When a hostname is given as a target, it is resolved via the Domain
217 Name System (DNS) to determine the IP address to scan. If the name
218 resolves to more than one IP address, only the first one will be
219 scanned. To make Nmap scan all the resolved addresses instead of only
220 the first one, use the --resolve-all option.
221 Sometimes you wish to scan a whole network of adjacent hosts. For this,
223 Nmap supports CIDR-style addressing. You can append /numbits to an IP
224 address or hostname and Nmap will scan every IP address for which the
225 first numbits are the same as for the reference IP or hostname given.
226 For example, 192.168.10.0/24 would scan the 256 hosts between
227 192.168.10.0 (binary: 11000000 10101000 00001010 00000000) and
228 192.168.10.255 (binary: 11000000 10101000 00001010 11111111),
229 inclusive. 192.168.10.40/24 would scan exactly the same targets. Given
230 that the host scanme.nmap.org is at the IP address 64.13.134.52, the
231 specification scanme.nmap.org/16 would scan the 65,536 IP addresses
232 between 64.13.0.0 and 64.13.255.255. The smallest allowed value is /0,
233 which targets the whole Internet. The largest value for IPv4 is /32,
234 which scans just the named host or IP address because all address bits
235 are fixed. The largest value for IPv6 is /128, which does the same
236 thing.
237 CIDR notation is short but not always flexible enough. For example, you
239 might want to scan 192.168.0.0/16 but skip any IPs ending with .0 or
240 .255 because they may be used as subnet network and broadcast
241 addresses. Nmap supports this through octet range addressing. Rather
242 than specify a normal IP address, you can specify a comma-separated
243 list of numbers or ranges for each octet. For example,
244 192.168.0-255.1-254 will skip all addresses in the range that end in .0
245 or .255, and 192.168.3-5,7.1 will scan the four addresses 192.168.3.1,
246 192.168.4.1, 192.168.5.1, and 192.168.7.1. Either side of a range may
247 be omitted; the default values are 0 on the left and 255 on the right.
248 Using - by itself is the same as 0-255, but remember to use 0- in the
249 first octet so the target specification doesn't look like a
250 command-line option. Ranges need not be limited to the final octets:
251 the specifier 0-255.0-255.13.37 will perform an Internet-wide scan for
252 all IP addresses ending in 13.37. This sort of broad sampling can be
253 useful for Internet surveys and research.
254 IPv6 addresses can be specified by their fully qualified IPv6 address
256 or hostname or with CIDR notation for subnets. Octet ranges aren't yet
257 supported for IPv6.
258 IPv6 addresses with non-global scope need to have a zone ID suffix. On
260 Unix systems, this is a percent sign followed by an interface name; a
261 complete address might be fe80::a8bb:ccff:fedd:eeff%eth0. On Windows,
262 use an interface index number in place of an interface name:
263 fe80::a8bb:ccff:fedd:eeff%1. You can see a list of interface indexes by
264 running the command netsh.exe interface ipv6 show interface.
265 Nmap accepts multiple host specifications on the command line, and they
267 don't need to be the same type. The command nmap scanme.nmap.org
268 192.168.0.0/8 10.0.0,1,3-7.- does what you would expect.
269 While targets are usually specified on the command lines, the following
271 options are also available to control target selection:
272 -iL inputfilename (Input from list)
274 Reads target specifications from inputfilename. Passing a huge list
275 of hosts is often awkward on the command line, yet it is a common
276 desire. For example, your DHCP server might export a list of 10,000
277 current leases that you wish to scan. Or maybe you want to scan all
278 IP addresses except for those to locate hosts using unauthorized
279 static IP addresses. Simply generate the list of hosts to scan and
280 pass that filename to Nmap as an argument to the -iL option.
281 Entries can be in any of the formats accepted by Nmap on the
282 command line (IP address, hostname, CIDR, IPv6, or octet ranges).
283 Each entry must be separated by one or more spaces, tabs, or
284 newlines. You can specify a hyphen (-) as the filename if you want
285 Nmap to read hosts from standard input rather than an actual file.
286 The input file may contain comments that start with # and extend to
288 the end of the line.
289 -iR num hosts (Choose random targets)
291 For Internet-wide surveys and other research, you may want to
292 choose targets at random. The num hosts argument tells Nmap how
293 many IPs to generate. Undesirable IPs such as those in certain
294 private, multicast, or unallocated address ranges are automatically
295 skipped. The argument 0 can be specified for a never-ending scan.
296 Keep in mind that some network administrators bristle at
297 unauthorized scans of their networks and may complain. Use this
298 option at your own risk! If you find yourself really bored one
299 rainy afternoon, try the command nmap -Pn -sS -p 80 -iR 0 --open to
300 locate random web servers for browsing.
301 --exclude host1[,host2[,...]] (Exclude hosts/networks)
303 Specifies a comma-separated list of targets to be excluded from the
304 scan even if they are part of the overall network range you
305 specify. The list you pass in uses normal Nmap syntax, so it can
306 include hostnames, CIDR netblocks, octet ranges, etc. This can be
307 useful when the network you wish to scan includes untouchable
308 mission-critical servers, systems that are known to react adversely
309 to port scans, or subnets administered by other people.
310 --excludefile exclude_file (Exclude list from file)
312 This offers the same functionality as the --exclude option, except
313 that the excluded targets are provided in a newline-, space-, or
314 tab-delimited exclude_file rather than on the command line.
315 The exclude file may contain comments that start with # and extend
317 to the end of the line.
318
320 One of the very first steps in any network reconnaissance mission is to
321 reduce a (sometimes huge) set of IP ranges into a list of active or
322 interesting hosts. Scanning every port of every single IP address is
323 slow and usually unnecessary. Of course what makes a host interesting
324 depends greatly on the scan purposes. Network administrators may only
325 be interested in hosts running a certain service, while security
326 auditors may care about every single device with an IP address. An
327 administrator may be comfortable using just an ICMP ping to locate
328 hosts on his internal network, while an external penetration tester may
329 use a diverse set of dozens of probes in an attempt to evade firewall
330 restrictions.
331 Because host discovery needs are so diverse, Nmap offers a wide variety
333 of options for customizing the techniques used. Host discovery is
334 sometimes called ping scan, but it goes well beyond the simple ICMP
335 echo request packets associated with the ubiquitous ping tool. Users
336 can skip the ping step entirely with a list scan (-sL) or by disabling
337 ping (-Pn), or engage the network with arbitrary combinations of
338 multi-port TCP SYN/ACK, UDP, SCTP INIT and ICMP probes. The goal of
339 these probes is to solicit responses which demonstrate that an IP
340 address is actually active (is being used by a host or network device).
341 On many networks, only a small percentage of IP addresses are active at
342 any given time. This is particularly common with private address space
343 such as 10.0.0.0/8. That network has 16 million IPs, but I have seen it
344 used by companies with less than a thousand machines. Host discovery
345 can find those machines in a sparsely allocated sea of IP addresses.
346 If no host discovery options are given, Nmap sends an ICMP echo
348 request, a TCP SYN packet to port 443, a TCP ACK packet to port 80, and
349 an ICMP timestamp request. (For IPv6, the ICMP timestamp request is
350 omitted because it is not part of ICMPv6.) These defaults are
351 equivalent to the -PE -PS443 -PA80 -PP options. The exceptions to this
352 are the ARP (for IPv4) and Neighbor Discovery (for IPv6) scans which
353 are used for any targets on a local ethernet network. For unprivileged
354 Unix shell users, the default probes are a SYN packet to ports 80 and
355 443 using the connect system call. This host discovery is often
356 sufficient when scanning local networks, but a more comprehensive set
357 of discovery probes is recommended for security auditing.
358 The -P* options (which select ping types) can be combined. You can
360 increase your odds of penetrating strict firewalls by sending many
361 probe types using different TCP ports/flags and ICMP codes. Also note
362 that ARP/Neighbor Discovery (-PR) is done by default against targets on
363 a local ethernet network even if you specify other -P* options, because
364 it is almost always faster and more effective.
365 By default, Nmap does host discovery and then performs a port scan
367 against each host it determines is online. This is true even if you
368 specify non-default host discovery types such as UDP probes (-PU). Read
369 about the -sn option to learn how to perform only host discovery, or
370 use -Pn to skip host discovery and port scan all target hosts. The
371 following options control host discovery:
372 -sL (List Scan)
374 The list scan is a degenerate form of host discovery that simply
375 lists each host of the network(s) specified, without sending any
376 packets to the target hosts. By default, Nmap still does
377 reverse-DNS resolution on the hosts to learn their names. It is
378 often surprising how much useful information simple hostnames give
379 out. For example, fw.chi is the name of one company's Chicago
380 firewall.
381 Nmap also reports the total number of IP addresses at the end. The
383 list scan is a good sanity check to ensure that you have proper IP
384 addresses for your targets. If the hosts sport domain names you do
385 not recognize, it is worth investigating further to prevent
386 scanning the wrong company's network.
387 Since the idea is to simply print a list of target hosts, options
389 for higher level functionality such as port scanning, OS detection,
390 or ping scanning cannot be combined with this. If you wish to
391 disable ping scanning while still performing such higher level
392 functionality, read up on the -Pn (skip ping) option.
393 -sn (No port scan)
395 This option tells Nmap not to do a port scan after host discovery,
396 and only print out the available hosts that responded to the host
397 discovery probes. This is often known as a “ping scan”, but you can
398 also request that traceroute and NSE host scripts be run. This is
399 by default one step more intrusive than the list scan, and can
400 often be used for the same purposes. It allows light reconnaissance
401 of a target network without attracting much attention. Knowing how
402 many hosts are up is more valuable to attackers than the list
403 provided by list scan of every single IP and host name.
404 Systems administrators often find this option valuable as well. It
406 can easily be used to count available machines on a network or
407 monitor server availability. This is often called a ping sweep, and
408 is more reliable than pinging the broadcast address because many
409 hosts do not reply to broadcast queries.
410 The default host discovery done with -sn consists of an ICMP echo
412 request, TCP SYN to port 443, TCP ACK to port 80, and an ICMP
413 timestamp request by default. When executed by an unprivileged
414 user, only SYN packets are sent (using a connect call) to ports 80
415 and 443 on the target. When a privileged user tries to scan targets
416 on a local ethernet network, ARP requests are used unless --send-ip
417 was specified. The -sn option can be combined with any of the
418 discovery probe types (the -P* options, excluding -Pn) for greater
419 flexibility. If any of those probe type and port number options are
420 used, the default probes are overridden. When strict firewalls are
421 in place between the source host running Nmap and the target
422 network, using those advanced techniques is recommended. Otherwise
423 hosts could be missed when the firewall drops probes or their
424 responses.
425 In previous releases of Nmap, -sn was known as -sP.
427 -Pn (No ping)
429 This option skips the Nmap discovery stage altogether. Normally,
430 Nmap uses this stage to determine active machines for heavier
431 scanning. By default, Nmap only performs heavy probing such as port
432 scans, version detection, or OS detection against hosts that are
433 found to be up. Disabling host discovery with -Pn causes Nmap to
434 attempt the requested scanning functions against every target IP
435 address specified. So if a class B target address space (/16) is
436 specified on the command line, all 65,536 IP addresses are scanned.
437 Proper host discovery is skipped as with the list scan, but instead
438 of stopping and printing the target list, Nmap continues to perform
439 requested functions as if each target IP is active. To skip ping
440 scan and port scan, while still allowing NSE to run, use the two
441 options -Pn -sn together.
442 For machines on a local ethernet network, ARP scanning will still
444 be performed (unless --disable-arp-ping or --send-ip is specified)
445 because Nmap needs MAC addresses to further scan target hosts. In
446 previous versions of Nmap, -Pn was -P0 and -PN.
447 -PS port list (TCP SYN Ping)
449 This option sends an empty TCP packet with the SYN flag set. The
450 default destination port is 80 (configurable at compile time by
451 changing DEFAULT_TCP_PROBE_PORT_SPEC in nmap.h). Alternate ports
452 can be specified as a parameter. The syntax is the same as for the
453 -p except that port type specifiers like T: are not allowed.
454 Examples are -PS22 and -PS22-25,80,113,1050,35000. Note that there
455 can be no space between -PS and the port list. If multiple probes
456 are specified they will be sent in parallel.
457 The SYN flag suggests to the remote system that you are attempting
459 to establish a connection. Normally the destination port will be
460 closed, and a RST (reset) packet sent back. If the port happens to
461 be open, the target will take the second step of a TCP
462 three-way-handshake by responding with a SYN/ACK TCP packet. The
463 machine running Nmap then tears down the nascent connection by
464 responding with a RST rather than sending an ACK packet which would
465 complete the three-way-handshake and establish a full connection.
466 The RST packet is sent by the kernel of the machine running Nmap in
467 response to the unexpected SYN/ACK, not by Nmap itself.
468 Nmap does not care whether the port is open or closed. Either the
470 RST or SYN/ACK response discussed previously tell Nmap that the
471 host is available and responsive.
472 On Unix boxes, only the privileged user root is generally able to
474 send and receive raw TCP packets. For unprivileged users, a
475 workaround is automatically employed whereby the connect system
476 call is initiated against each target port. This has the effect of
477 sending a SYN packet to the target host, in an attempt to establish
478 a connection. If connect returns with a quick success or an
479 ECONNREFUSED failure, the underlying TCP stack must have received a
480 SYN/ACK or RST and the host is marked available. If the connection
481 attempt is left hanging until a timeout is reached, the host is
482 marked as down.
483 -PA port list (TCP ACK Ping)
485 The TCP ACK ping is quite similar to the just-discussed SYN ping.
486 The difference, as you could likely guess, is that the TCP ACK flag
487 is set instead of the SYN flag. Such an ACK packet purports to be
488 acknowledging data over an established TCP connection, but no such
489 connection exists. So remote hosts should always respond with a RST
490 packet, disclosing their existence in the process.
491 The -PA option uses the same default port as the SYN probe (80) and
493 can also take a list of destination ports in the same format. If an
494 unprivileged user tries this, the connect workaround discussed
495 previously is used. This workaround is imperfect because connect is
496 actually sending a SYN packet rather than an ACK.
497 The reason for offering both SYN and ACK ping probes is to maximize
499 the chances of bypassing firewalls. Many administrators configure
500 routers and other simple firewalls to block incoming SYN packets
501 except for those destined for public services like the company web
502 site or mail server. This prevents other incoming connections to
503 the organization, while allowing users to make unobstructed
504 outgoing connections to the Internet. This non-stateful approach
505 takes up few resources on the firewall/router and is widely
506 supported by hardware and software filters. The Linux
507 Netfilter/iptables firewall software offers the --syn convenience
508 option to implement this stateless approach. When stateless
509 firewall rules such as this are in place, SYN ping probes (-PS) are
510 likely to be blocked when sent to closed target ports. In such
511 cases, the ACK probe shines as it cuts right through these rules.
512 Another common type of firewall uses stateful rules that drop
514 unexpected packets. This feature was initially found mostly on
515 high-end firewalls, though it has become much more common over the
516 years. The Linux Netfilter/iptables system supports this through
517 the --state option, which categorizes packets based on connection
518 state. A SYN probe is more likely to work against such a system, as
519 unexpected ACK packets are generally recognized as bogus and
520 dropped. A solution to this quandary is to send both SYN and ACK
521 probes by specifying -PS and -PA.
522 -PU port list (UDP Ping)
524 Another host discovery option is the UDP ping, which sends a UDP
525 packet to the given ports. For most ports, the packet will be
526 empty, though some use a protocol-specific payload that is more
527 likely to elicit a response. The payload database is described at
528 https://nmap.org/book/nmap-payloads.html.
529 . Packet content can also be affected with the --data,
531 --data-string, and --data-length options.
532 The port list takes the same format as with the previously
534 discussed -PS and -PA options. If no ports are specified, the
535 default is 40125. This default can be configured at compile-time
536 by changing DEFAULT_UDP_PROBE_PORT_SPEC in nmap.h. A highly
537 uncommon port is used by default because sending to open ports is
538 often undesirable for this particular scan type.
539 Upon hitting a closed port on the target machine, the UDP probe
541 should elicit an ICMP port unreachable packet in return. This
542 signifies to Nmap that the machine is up and available. Many other
543 types of ICMP errors, such as host/network unreachables or TTL
544 exceeded are indicative of a down or unreachable host. A lack of
545 response is also interpreted this way. If an open port is reached,
546 most services simply ignore the empty packet and fail to return any
547 response. This is why the default probe port is 40125, which is
548 highly unlikely to be in use. A few services, such as the Character
549 Generator (chargen) protocol, will respond to an empty UDP packet,
550 and thus disclose to Nmap that the machine is available.
551 The primary advantage of this scan type is that it bypasses
553 firewalls and filters that only screen TCP. For example, I once
554 owned a Linksys BEFW11S4 wireless broadband router. The external
555 interface of this device filtered all TCP ports by default, but UDP
556 probes would still elicit port unreachable messages and thus give
557 away the device.
558 -PY port list (SCTP INIT Ping)
560 This option sends an SCTP packet containing a minimal INIT chunk.
561 The default destination port is 80 (configurable at compile time by
562 changing DEFAULT_SCTP_PROBE_PORT_SPEC in nmap.h). Alternate ports
563 can be specified as a parameter. The syntax is the same as for the
564 -p except that port type specifiers like S: are not allowed.
565 Examples are -PY22 and -PY22,80,179,5060. Note that there can be no
566 space between -PY and the port list. If multiple probes are
567 specified they will be sent in parallel.
568 The INIT chunk suggests to the remote system that you are
570 attempting to establish an association. Normally the destination
571 port will be closed, and an ABORT chunk will be sent back. If the
572 port happens to be open, the target will take the second step of an
573 SCTP four-way-handshake by responding with an INIT-ACK chunk. If
574 the machine running Nmap has a functional SCTP stack, then it tears
575 down the nascent association by responding with an ABORT chunk
576 rather than sending a COOKIE-ECHO chunk which would be the next
577 step in the four-way-handshake. The ABORT packet is sent by the
578 kernel of the machine running Nmap in response to the unexpected
579 INIT-ACK, not by Nmap itself.
580 Nmap does not care whether the port is open or closed. Either the
582 ABORT or INIT-ACK response discussed previously tell Nmap that the
583 host is available and responsive.
584 On Unix boxes, only the privileged user root is generally able to
586 send and receive raw SCTP packets. Using SCTP INIT Pings is
587 currently not possible for unprivileged users.
588 -PE; -PP; -PM (ICMP Ping Types)
590 In addition to the unusual TCP, UDP and SCTP host discovery types
591 discussed previously, Nmap can send the standard packets sent by
592 the ubiquitous ping program. Nmap sends an ICMP type 8 (echo
593 request) packet to the target IP addresses, expecting a type 0
594 (echo reply) in return from available hosts. Unfortunately for
595 network explorers, many hosts and firewalls now block these
596 packets, rather than responding as required by RFC 1122[2]. For
597 this reason, ICMP-only scans are rarely reliable enough against
598 unknown targets over the Internet. But for system administrators
599 monitoring an internal network, they can be a practical and
600 efficient approach. Use the -PE option to enable this echo request
601 behavior.
602 While echo request is the standard ICMP ping query, Nmap does not
604 stop there. The ICMP standards (RFC 792[3] and RFC 950[4] ) also
605 specify timestamp request, information request, and address mask
606 request packets as codes 13, 15, and 17, respectively. While the
607 ostensible purpose for these queries is to learn information such
608 as address masks and current times, they can easily be used for
609 host discovery. A system that replies is up and available. Nmap
610 does not currently implement information request packets, as they
611 are not widely supported. RFC 1122 insists that “a host SHOULD NOT
612 implement these messages”. Timestamp and address mask queries can
613 be sent with the -PP and -PM options, respectively. A timestamp
614 reply (ICMP code 14) or address mask reply (code 18) discloses that
615 the host is available. These two queries can be valuable when
616 administrators specifically block echo request packets while
617 forgetting that other ICMP queries can be used for the same
618 purpose.
619 -PO protocol list (IP Protocol Ping)
621 One of the newer host discovery options is the IP protocol ping,
622 which sends IP packets with the specified protocol number set in
623 their IP header. The protocol list takes the same format as do port
624 lists in the previously discussed TCP, UDP and SCTP host discovery
625 options. If no protocols are specified, the default is to send
626 multiple IP packets for ICMP (protocol 1), IGMP (protocol 2), and
627 IP-in-IP (protocol 4). The default protocols can be configured at
628 compile-time by changing DEFAULT_PROTO_PROBE_PORT_SPEC in nmap.h.
629 Note that for the ICMP, IGMP, TCP (protocol 6), UDP (protocol 17)
630 and SCTP (protocol 132), the packets are sent with the proper
631 protocol headers while other protocols are sent with no additional
632 data beyond the IP header (unless any of --data, --data-string, or
633 --data-length options are specified).
634 This host discovery method looks for either responses using the
636 same protocol as a probe, or ICMP protocol unreachable messages
637 which signify that the given protocol isn't supported on the
638 destination host. Either type of response signifies that the target
639 host is alive.
640 -PR (ARP Ping)
642 One of the most common Nmap usage scenarios is to scan an ethernet
643 LAN. On most LANs, especially those using private address ranges
644 specified by RFC 1918[5], the vast majority of IP addresses are
645 unused at any given time. When Nmap tries to send a raw IP packet
646 such as an ICMP echo request, the operating system must determine
647 the destination hardware (ARP) address corresponding to the target
648 IP so that it can properly address the ethernet frame. This is
649 often slow and problematic, since operating systems weren't written
650 with the expectation that they would need to do millions of ARP
651 requests against unavailable hosts in a short time period.
652 ARP scan puts Nmap and its optimized algorithms in charge of ARP
654 requests. And if it gets a response back, Nmap doesn't even need to
655 worry about the IP-based ping packets since it already knows the
656 host is up. This makes ARP scan much faster and more reliable than
657 IP-based scans. So it is done by default when scanning ethernet
658 hosts that Nmap detects are on a local ethernet network. Even if
659 different ping types (such as -PE or -PS) are specified, Nmap uses
660 ARP instead for any of the targets which are on the same LAN. If
661 you absolutely don't want to do an ARP scan, specify
662 --disable-arp-ping.
663 For IPv6 (-6 option), -PR uses ICMPv6 Neighbor Discovery instead of
665 ARP. Neighbor Discovery, defined in RFC 4861, can be seen as the
666 IPv6 equivalent of ARP.
667 --disable-arp-ping (No ARP or ND Ping)
669 Nmap normally does ARP or IPv6 Neighbor Discovery (ND) discovery of
670 locally connected ethernet hosts, even if other host discovery
671 options such as -Pn or -PE are used. To disable this implicit
672 behavior, use the --disable-arp-ping option.
673 The default behavior is normally faster, but this option is useful
675 on networks using proxy ARP, in which a router speculatively
676 replies to all ARP requests, making every target appear to be up
677 according to ARP scan.
678 --traceroute (Trace path to host)
680 Traceroutes are performed post-scan using information from the scan
681 results to determine the port and protocol most likely to reach the
682 target. It works with all scan types except connect scans (-sT) and
683 idle scans (-sI). All traces use Nmap's dynamic timing model and
684 are performed in parallel.
685 Traceroute works by sending packets with a low TTL (time-to-live)
687 in an attempt to elicit ICMP Time Exceeded messages from
688 intermediate hops between the scanner and the target host. Standard
689 traceroute implementations start with a TTL of 1 and increment the
690 TTL until the destination host is reached. Nmap's traceroute starts
691 with a high TTL and then decrements the TTL until it reaches zero.
692 Doing it backwards lets Nmap employ clever caching algorithms to
693 speed up traces over multiple hosts. On average Nmap sends 5–10
694 fewer packets per host, depending on network conditions. If a
695 single subnet is being scanned (i.e. 192.168.0.0/24) Nmap may only
696 have to send two packets to most hosts.
697 -n (No DNS resolution)
699 Tells Nmap to never do reverse DNS
700 resolution on the active IP addresses it finds. Since DNS can be
702 slow even with Nmap's built-in parallel stub resolver, this option
703 can slash scanning times.
704 -R (DNS resolution for all targets)
706 Tells Nmap to always do reverse DNS resolution on the target IP
707 addresses. Normally reverse DNS is only performed against
708 responsive (online) hosts.
709 --resolve-all (Scan each resolved address)
711 If a hostname target resolves to more than one address, scan all of
712 them. The default behavior is to only scan the first resolved
713 address. Regardless, only addresses in the appropriate address
714 family will be scanned: IPv4 by default, IPv6 with -6.
715 --system-dns (Use system DNS resolver)
717 By default, Nmap reverse-resolves IP addresses by sending queries
718 directly to the name servers configured on your host and then
719 listening for responses. Many requests (often dozens) are performed
720 in parallel to improve performance. Specify this option to use your
721 system resolver instead (one IP at a time via the getnameinfo
722 call). This is slower and rarely useful unless you find a bug in
723 the Nmap parallel resolver (please let us know if you do). The
724 system resolver is always used for forward lookups (getting an IP
725 address from a hostname).
726 --dns-servers server1[,server2[,...]] (Servers to use for reverse DNS
728 queries)
729 By default, Nmap determines your DNS servers (for rDNS resolution)
730 from your resolv.conf file (Unix) or the Registry (Win32).
731 Alternatively, you may use this option to specify alternate
732 servers. This option is not honored if you are using --system-dns.
733 Using multiple DNS servers is often faster, especially if you
734 choose authoritative servers for your target IP space. This option
735 can also improve stealth, as your requests can be bounced off just
736 about any recursive DNS server on the Internet.
737 This option also comes in handy when scanning private networks.
739 Sometimes only a few name servers provide proper rDNS information,
740 and you may not even know where they are. You can scan the network
741 for port 53 (perhaps with version detection), then try Nmap list
742 scans (-sL) specifying each name server one at a time with
743 --dns-servers until you find one which works.
744 This option might not be honored if the DNS response exceeds the
746 size of a UDP packet. In such a situation our DNS resolver will
747 make the best effort to extract a response from the truncated
748 packet, and if not successful it will fall back to using the system
749 resolver. Also, responses that contain CNAME aliases will fall back
750 to the system resolver.
751
753 While Nmap has grown in functionality over the years, it began as an
754 efficient port scanner, and that remains its core function. The simple
755 command nmap target scans 1,000 TCP ports on the host target. While
756 many port scanners have traditionally lumped all ports into the open or
757 closed states, Nmap is much more granular. It divides ports into six
758 states: open, closed, filtered, unfiltered, open|filtered, or
759 closed|filtered.
760 These states are not intrinsic properties of the port itself, but
762 describe how Nmap sees them. For example, an Nmap scan from the same
763 network as the target may show port 135/tcp as open, while a scan at
764 the same time with the same options from across the Internet might show
765 that port as filtered.
766 The six port states recognized by Nmap
768 open
770 An application is actively accepting TCP connections, UDP datagrams
771 or SCTP associations on this port. Finding these is often the
772 primary goal of port scanning. Security-minded people know that
773 each open port is an avenue for attack. Attackers and pen-testers
774 want to exploit the open ports, while administrators try to close
775 or protect them with firewalls without thwarting legitimate users.
776 Open ports are also interesting for non-security scans because they
777 show services available for use on the network.
778 closed
780 A closed port is accessible (it receives and responds to Nmap probe
781 packets), but there is no application listening on it. They can be
782 helpful in showing that a host is up on an IP address (host
783 discovery, or ping scanning), and as part of OS detection. Because
784 closed ports are reachable, it may be worth scanning later in case
785 some open up. Administrators may want to consider blocking such
786 ports with a firewall. Then they would appear in the filtered
787 state, discussed next.
788 filtered
790 Nmap cannot determine whether the port is open because packet
791 filtering prevents its probes from reaching the port. The filtering
792 could be from a dedicated firewall device, router rules, or
793 host-based firewall software. These ports frustrate attackers
794 because they provide so little information. Sometimes they respond
795 with ICMP error messages such as type 3 code 13 (destination
796 unreachable: communication administratively prohibited), but
797 filters that simply drop probes without responding are far more
798 common. This forces Nmap to retry several times just in case the
799 probe was dropped due to network congestion rather than filtering.
800 This slows down the scan dramatically.
801 unfiltered
803 The unfiltered state means that a port is accessible, but Nmap is
804 unable to determine whether it is open or closed. Only the ACK
805 scan, which is used to map firewall rulesets, classifies ports into
806 this state. Scanning unfiltered ports with other scan types such as
807 Window scan, SYN scan, or FIN scan, may help resolve whether the
808 port is open.
809 open|filtered
811 Nmap places ports in this state when it is unable to determine
812 whether a port is open or filtered. This occurs for scan types in
813 which open ports give no response. The lack of response could also
814 mean that a packet filter dropped the probe or any response it
815 elicited. So Nmap does not know for sure whether the port is open
816 or being filtered. The UDP, IP protocol, FIN, NULL, and Xmas scans
817 classify ports this way.
818 closed|filtered
820 This state is used when Nmap is unable to determine whether a port
821 is closed or filtered. It is only used for the IP ID idle scan.
822
824 As a novice performing automotive repair, I can struggle for hours
825 trying to fit my rudimentary tools (hammer, duct tape, wrench, etc.) to
826 the task at hand. When I fail miserably and tow my jalopy to a real
827 mechanic, he invariably fishes around in a huge tool chest until
828 pulling out the perfect gizmo which makes the job seem effortless. The
829 art of port scanning is similar. Experts understand the dozens of scan
830 techniques and choose the appropriate one (or combination) for a given
831 task. Inexperienced users and script kiddies, on the other hand, try to
832 solve every problem with the default SYN scan. Since Nmap is free, the
833 only barrier to port scanning mastery is knowledge. That certainly
834 beats the automotive world, where it may take great skill to determine
835 that you need a strut spring compressor, then you still have to pay
836 thousands of dollars for it.
837 Most of the scan types are only available to privileged users. This is
839 because they send and receive raw packets, which requires root access
840 on Unix systems. Using an administrator account on Windows is
841 recommended, though Nmap sometimes works for unprivileged users on that
842 platform when Npcap has already been loaded into the OS. Requiring root
843 privileges was a serious limitation when Nmap was released in 1997, as
844 many users only had access to shared shell accounts. Now, the world is
845 different. Computers are cheaper, far more people have always-on direct
846 Internet access, and desktop Unix systems (including Linux and Mac OS
847 X) are prevalent. A Windows version of Nmap is now available, allowing
848 it to run on even more desktops. For all these reasons, users have less
849 need to run Nmap from limited shared shell accounts. This is fortunate,
850 as the privileged options make Nmap far more powerful and flexible.
851 While Nmap attempts to produce accurate results, keep in mind that all
853 of its insights are based on packets returned by the target machines
854 (or firewalls in front of them). Such hosts may be untrustworthy and
855 send responses intended to confuse or mislead Nmap. Much more common
856 are non-RFC-compliant hosts that do not respond as they should to Nmap
857 probes. FIN, NULL, and Xmas scans are particularly susceptible to this
858 problem. Such issues are specific to certain scan types and so are
859 discussed in the individual scan type entries.
860 This section documents the dozen or so port scan techniques supported
862 by Nmap. Only one method may be used at a time, except that UDP scan
863 (-sU) and any one of the SCTP scan types (-sY, -sZ) may be combined
864 with any one of the TCP scan types. As a memory aid, port scan type
865 options are of the form -sC, where C is a prominent character in the
866 scan name, usually the first. The one exception to this is the
867 deprecated FTP bounce scan (-b). By default, Nmap performs a SYN Scan,
868 though it substitutes a connect scan if the user does not have proper
869 privileges to send raw packets (requires root access on Unix). Of the
870 scans listed in this section, unprivileged users can only execute
871 connect and FTP bounce scans.
872 -sS (TCP SYN scan)
874 SYN scan is the default and most popular scan option for good
875 reasons. It can be performed quickly, scanning thousands of ports
876 per second on a fast network not hampered by restrictive firewalls.
877 It is also relatively unobtrusive and stealthy since it never
878 completes TCP connections. SYN scan works against any compliant TCP
879 stack rather than depending on idiosyncrasies of specific platforms
880 as Nmap's FIN/NULL/Xmas, Maimon and idle scans do. It also allows
881 clear, reliable differentiation between the open, closed, and
882 filtered states.
883 This technique is often referred to as half-open scanning, because
885 you don't open a full TCP connection. You send a SYN packet, as if
886 you are going to open a real connection and then wait for a
887 response. A SYN/ACK indicates the port is listening (open), while a
888 RST (reset) is indicative of a non-listener. If no response is
889 received after several retransmissions, the port is marked as
890 filtered. The port is also marked filtered if an ICMP unreachable
891 error (type 3, code 0, 1, 2, 3, 9, 10, or 13) is received. The port
892 is also considered open if a SYN packet (without the ACK flag) is
893 received in response. This can be due to an extremely rare TCP
894 feature known as a simultaneous open or split handshake connection
895 (see https://nmap.org/misc/split-handshake.pdf).
896 -sT (TCP connect scan)
898 TCP connect scan is the default TCP scan type when SYN scan is not
899 an option. This is the case when a user does not have raw packet
900 privileges. Instead of writing raw packets as most other scan types
901 do, Nmap asks the underlying operating system to establish a
902 connection with the target machine and port by issuing the connect
903 system call. This is the same high-level system call that web
904 browsers, P2P clients, and most other network-enabled applications
905 use to establish a connection. It is part of a programming
906 interface known as the Berkeley Sockets API. Rather than read raw
907 packet responses off the wire, Nmap uses this API to obtain status
908 information on each connection attempt.
909 When SYN scan is available, it is usually a better choice. Nmap has
911 less control over the high level connect call than with raw
912 packets, making it less efficient. The system call completes
913 connections to open target ports rather than performing the
914 half-open reset that SYN scan does. Not only does this take longer
915 and require more packets to obtain the same information, but target
916 machines are more likely to log the connection. A decent IDS will
917 catch either, but most machines have no such alarm system. Many
918 services on your average Unix system will add a note to syslog, and
919 sometimes a cryptic error message, when Nmap connects and then
920 closes the connection without sending data. Truly pathetic services
921 crash when this happens, though that is uncommon. An administrator
922 who sees a bunch of connection attempts in her logs from a single
923 system should know that she has been connect scanned.
924 -sU (UDP scans)
926 While most popular services on the Internet run over the TCP
927 protocol, UDP[6] services are widely deployed. DNS, SNMP, and DHCP
928 (registered ports 53, 161/162, and 67/68) are three of the most
929 common. Because UDP scanning is generally slower and more difficult
930 than TCP, some security auditors ignore these ports. This is a
931 mistake, as exploitable UDP services are quite common and attackers
932 certainly don't ignore the whole protocol. Fortunately, Nmap can
933 help inventory UDP ports.
934 UDP scan is activated with the -sU option. It can be combined with
936 a TCP scan type such as SYN scan (-sS) to check both protocols
937 during the same run.
938 UDP scan works by sending a UDP packet to every targeted port. For
940 some common ports such as 53 and 161, a protocol-specific payload
941 is sent to increase response rate, but for most ports the packet is
942 empty unless the --data, --data-string, or --data-length options
943 are specified. If an ICMP port unreachable error (type 3, code 3)
944 is returned, the port is closed. Other ICMP unreachable errors
945 (type 3, codes 0, 1, 2, 9, 10, or 13) mark the port as filtered.
946 Occasionally, a service will respond with a UDP packet, proving
947 that it is open. If no response is received after retransmissions,
948 the port is classified as open|filtered. This means that the port
949 could be open, or perhaps packet filters are blocking the
950 communication. Version detection (-sV) can be used to help
951 differentiate the truly open ports from the filtered ones.
952 A big challenge with UDP scanning is doing it quickly. Open and
954 filtered ports rarely send any response, leaving Nmap to time out
955 and then conduct retransmissions just in case the probe or response
956 were lost. Closed ports are often an even bigger problem. They
957 usually send back an ICMP port unreachable error. But unlike the
958 RST packets sent by closed TCP ports in response to a SYN or
959 connect scan, many hosts rate limit ICMP port unreachable messages
960 by default. Linux and Solaris are particularly strict about this.
961 For example, the Linux 2.4.20 kernel limits destination unreachable
962 messages to one per second (in net/ipv4/icmp.c).
963 Nmap detects rate limiting and slows down accordingly to avoid
965 flooding the network with useless packets that the target machine
966 will drop. Unfortunately, a Linux-style limit of one packet per
967 second makes a 65,536-port scan take more than 18 hours. Ideas for
968 speeding your UDP scans up include scanning more hosts in parallel,
969 doing a quick scan of just the popular ports first, scanning from
970 behind the firewall, and using --host-timeout to skip slow hosts.
971 -sY (SCTP INIT scan)
973 SCTP[7] is a relatively new alternative to the TCP and UDP
974 protocols, combining most characteristics of TCP and UDP, and also
975 adding new features like multi-homing and multi-streaming. It is
976 mostly being used for SS7/SIGTRAN related services but has the
977 potential to be used for other applications as well. SCTP INIT scan
978 is the SCTP equivalent of a TCP SYN scan. It can be performed
979 quickly, scanning thousands of ports per second on a fast network
980 not hampered by restrictive firewalls. Like SYN scan, INIT scan is
981 relatively unobtrusive and stealthy, since it never completes SCTP
982 associations. It also allows clear, reliable differentiation
983 between the open, closed, and filtered states.
984 This technique is often referred to as half-open scanning, because
986 you don't open a full SCTP association. You send an INIT chunk, as
987 if you are going to open a real association and then wait for a
988 response. An INIT-ACK chunk indicates the port is listening (open),
989 while an ABORT chunk is indicative of a non-listener. If no
990 response is received after several retransmissions, the port is
991 marked as filtered. The port is also marked filtered if an ICMP
992 unreachable error (type 3, code 0, 1, 2, 3, 9, 10, or 13) is
993 received.
994 -sN; -sF; -sX (TCP NULL, FIN, and Xmas scans)
996 These three scan types (even more are possible with the --scanflags
997 option described in the next section) exploit a subtle loophole in
998 the TCP RFC[8] to differentiate between open and closed ports. Page
999 65 of RFC 793 says that “if the [destination] port state is CLOSED
1000 .... an incoming segment not containing a RST causes a RST to be
1001 sent in response.” Then the next page discusses packets sent to
1002 open ports without the SYN, RST, or ACK bits set, stating that:
1003 “you are unlikely to get here, but if you do, drop the segment, and
1004 return.”
1005 When scanning systems compliant with this RFC text, any packet not
1007 containing SYN, RST, or ACK bits will result in a returned RST if
1008 the port is closed and no response at all if the port is open. As
1009 long as none of those three bits are included, any combination of
1010 the other three (FIN, PSH, and URG) are OK. Nmap exploits this with
1011 three scan types:
1012 Null scan (-sN)
1014 Does not set any bits (TCP flag header is 0)
1015 FIN scan (-sF)
1017 Sets just the TCP FIN bit.
1018 Xmas scan (-sX)
1020 Sets the FIN, PSH, and URG flags, lighting the packet up like a
1021 Christmas tree.
1022 These three scan types are exactly the same in behavior except for
1024 the TCP flags set in probe packets. If a RST packet is received,
1025 the port is considered closed, while no response means it is
1026 open|filtered. The port is marked filtered if an ICMP unreachable
1027 error (type 3, code 0, 1, 2, 3, 9, 10, or 13) is received.
1028 The key advantage to these scan types is that they can sneak
1030 through certain non-stateful firewalls and packet filtering
1031 routers. Another advantage is that these scan types are a little
1032 more stealthy than even a SYN scan. Don't count on this though—most
1033 modern IDS products can be configured to detect them. The big
1034 downside is that not all systems follow RFC 793 to the letter. A
1035 number of systems send RST responses to the probes regardless of
1036 whether the port is open or not. This causes all of the ports to be
1037 labeled closed. Major operating systems that do this are Microsoft
1038 Windows, many Cisco devices, BSDI, and IBM OS/400. This scan does
1039 work against most Unix-based systems though. Another downside of
1040 these scans is that they can't distinguish open ports from certain
1041 filtered ones, leaving you with the response open|filtered.
1042 -sA (TCP ACK scan)
1044 This scan is different than the others discussed so far in that it
1045 never determines open (or even open|filtered) ports. It is used to
1046 map out firewall rulesets, determining whether they are stateful or
1047 not and which ports are filtered.
1048 The ACK scan probe packet has only the ACK flag set (unless you use
1050 --scanflags). When scanning unfiltered systems, open and closed
1051 ports will both return a RST packet. Nmap then labels them as
1052 unfiltered, meaning that they are reachable by the ACK packet, but
1053 whether they are open or closed is undetermined. Ports that don't
1054 respond, or send certain ICMP error messages back (type 3, code 0,
1055 1, 2, 3, 9, 10, or 13), are labeled filtered.
1056 -sW (TCP Window scan)
1058 Window scan is exactly the same as ACK scan except that it exploits
1059 an implementation detail of certain systems to differentiate open
1060 ports from closed ones, rather than always printing unfiltered when
1061 a RST is returned. It does this by examining the TCP Window field
1062 of the RST packets returned. On some systems, open ports use a
1063 positive window size (even for RST packets) while closed ones have
1064 a zero window. So instead of always listing a port as unfiltered
1065 when it receives a RST back, Window scan lists the port as open or
1066 closed if the TCP Window value in that reset is positive or zero,
1067 respectively.
1068 This scan relies on an implementation detail of a minority of
1070 systems out on the Internet, so you can't always trust it. Systems
1071 that don't support it will usually return all ports closed. Of
1072 course, it is possible that the machine really has no open ports.
1073 If most scanned ports are closed but a few common port numbers
1074 (such as 22, 25, 53) are filtered, the system is most likely
1075 susceptible. Occasionally, systems will even show the exact
1076 opposite behavior. If your scan shows 1,000 open ports and three
1077 closed or filtered ports, then those three may very well be the
1078 truly open ones.
1079 -sM (TCP Maimon scan)
1081 The Maimon scan is named after its discoverer, Uriel Maimon. He
1082 described the technique in Phrack Magazine issue #49 (November
1083 1996). Nmap, which included this technique, was released two
1084 issues later. This technique is exactly the same as NULL, FIN, and
1085 Xmas scans, except that the probe is FIN/ACK. According to RFC
1086 793[8] (TCP), a RST packet should be generated in response to such
1087 a probe whether the port is open or closed. However, Uriel noticed
1088 that many BSD-derived systems simply drop the packet if the port is
1089 open.
1090 --scanflags (Custom TCP scan)
1092 Truly advanced Nmap users need not limit themselves to the canned
1093 scan types offered. The --scanflags option allows you to design
1094 your own scan by specifying arbitrary TCP flags. Let your creative
1095 juices flow, while evading intrusion detection systems whose
1096 vendors simply paged through the Nmap man page adding specific
1097 rules!
1098 The --scanflags argument can be a numerical flag value such as 9
1100 (PSH and FIN), but using symbolic names is easier. Just mash
1101 together any combination of URG, ACK, PSH, RST, SYN, and FIN. For
1102 example, --scanflags URGACKPSHRSTSYNFIN sets everything, though
1103 it's not very useful for scanning. The order these are specified in
1104 is irrelevant.
1105 In addition to specifying the desired flags, you can specify a TCP
1107 scan type (such as -sA or -sF). That base type tells Nmap how to
1108 interpret responses. For example, a SYN scan considers no-response
1109 to indicate a filtered port, while a FIN scan treats the same as
1110 open|filtered. Nmap will behave the same way it does for the base
1111 scan type, except that it will use the TCP flags you specify
1112 instead. If you don't specify a base type, SYN scan is used.
1113 -sZ (SCTP COOKIE ECHO scan)
1115 SCTP COOKIE ECHO scan is a more advanced SCTP scan. It takes
1116 advantage of the fact that SCTP implementations should silently
1117 drop packets containing COOKIE ECHO chunks on open ports, but send
1118 an ABORT if the port is closed. The advantage of this scan type is
1119 that it is not as obvious a port scan than an INIT scan. Also,
1120 there may be non-stateful firewall rulesets blocking INIT chunks,
1121 but not COOKIE ECHO chunks. Don't be fooled into thinking that this
1122 will make a port scan invisible; a good IDS will be able to detect
1123 SCTP COOKIE ECHO scans too. The downside is that SCTP COOKIE ECHO
1124 scans cannot differentiate between open and filtered ports, leaving
1125 you with the state open|filtered in both cases.
1126 -sI zombie host[:probeport] (idle scan)
1128 This advanced scan method allows for a truly blind TCP port scan of
1129 the target (meaning no packets are sent to the target from your
1130 real IP address). Instead, a unique side-channel attack exploits
1131 predictable IP fragmentation ID sequence generation on the zombie
1132 host to glean information about the open ports on the target. IDS
1133 systems will display the scan as coming from the zombie machine you
1134 specify (which must be up and meet certain criteria). This
1135 fascinating scan type is too complex to fully describe in this
1136 reference guide, so I wrote and posted an informal paper with full
1137 details at https://nmap.org/book/idlescan.html.
1138 Besides being extraordinarily stealthy (due to its blind nature),
1140 this scan type permits mapping out IP-based trust relationships
1141 between machines. The port listing shows open ports from the
1142 perspective of the zombie host. So you can try scanning a target
1143 using various zombies that you think might be trusted (via
1144 router/packet filter rules).
1145 You can add a colon followed by a port number to the zombie host if
1147 you wish to probe a particular port on the zombie for IP ID
1148 changes. Otherwise Nmap will use the port it uses by default for
1149 TCP pings (80).
1150 -sO (IP protocol scan)
1152 IP protocol scan allows you to determine which IP protocols (TCP,
1153 ICMP, IGMP, etc.) are supported by target machines. This isn't
1154 technically a port scan, since it cycles through IP protocol
1155 numbers rather than TCP or UDP port numbers. Yet it still uses the
1156 -p option to select scanned protocol numbers, reports its results
1157 within the normal port table format, and even uses the same
1158 underlying scan engine as the true port scanning methods. So it is
1159 close enough to a port scan that it belongs here.
1160 Besides being useful in its own right, protocol scan demonstrates
1162 the power of open-source software. While the fundamental idea is
1163 pretty simple, I had not thought to add it nor received any
1164 requests for such functionality. Then in the summer of 2000,
1165 Gerhard Rieger conceived the idea, wrote an excellent patch
1166 implementing it, and sent it to the announce mailing list (then
1167 called nmap-hackers). I incorporated that patch into the Nmap tree
1168 and released a new version the next day. Few pieces of commercial
1169 software have users enthusiastic enough to design and contribute
1170 their own improvements!
1171 Protocol scan works in a similar fashion to UDP scan. Instead of
1173 iterating through the port number field of a UDP packet, it sends
1174 IP packet headers and iterates through the eight-bit IP protocol
1175 field. The headers are usually empty, containing no data and not
1176 even the proper header for the claimed protocol. The exceptions are
1177 TCP, UDP, ICMP, SCTP, and IGMP. A proper protocol header for those
1178 is included since some systems won't send them otherwise and
1179 because Nmap already has functions to create them. Instead of
1180 watching for ICMP port unreachable messages, protocol scan is on
1181 the lookout for ICMP protocol unreachable messages. If Nmap
1182 receives any response in any protocol from the target host, Nmap
1183 marks that protocol as open. An ICMP protocol unreachable error
1184 (type 3, code 2) causes the protocol to be marked as closed while
1185 port unreachable (type 3, code 3) marks the protocol open. Other
1186 ICMP unreachable errors (type 3, code 0, 1, 9, 10, or 13) cause the
1187 protocol to be marked filtered (though they prove that ICMP is open
1188 at the same time). If no response is received after
1189 retransmissions, the protocol is marked open|filtered
1190 -b FTP relay host (FTP bounce scan)
1192 An interesting feature of the FTP protocol (RFC 959[9]) is support
1193 for so-called proxy FTP connections. This allows a user to connect
1194 to one FTP server, then ask that files be sent to a third-party
1195 server. Such a feature is ripe for abuse on many levels, so most
1196 servers have ceased supporting it. One of the abuses this feature
1197 allows is causing the FTP server to port scan other hosts. Simply
1198 ask the FTP server to send a file to each interesting port of a
1199 target host in turn. The error message will describe whether the
1200 port is open or not. This is a good way to bypass firewalls because
1201 organizational FTP servers are often placed where they have more
1202 access to other internal hosts than any old Internet host would.
1203 Nmap supports FTP bounce scan with the -b option. It takes an
1204 argument of the form username:password@server:port. Server is the
1205 name or IP address of a vulnerable FTP server. As with a normal
1206 URL, you may omit username:password, in which case anonymous login
1207 credentials (user: anonymous password:-wwwuser@) are used. The port
1208 number (and preceding colon) may be omitted as well, in which case
1209 the default FTP port (21) on server is used.
1210 This vulnerability was widespread in 1997 when Nmap was released,
1212 but has largely been fixed. Vulnerable servers are still around, so
1213 it is worth trying when all else fails. If bypassing a firewall is
1214 your goal, scan the target network for port 21 (or even for any FTP
1215 services if you scan all ports with version detection) and use the
1216 ftp-bounce NSE script. Nmap will tell you whether the host is
1217 vulnerable or not. If you are just trying to cover your tracks, you
1218 don't need to (and, in fact, shouldn't) limit yourself to hosts on
1219 the target network. Before you go scanning random Internet
1220 addresses for vulnerable FTP servers, consider that sysadmins may
1221 not appreciate you abusing their servers in this way.
1222
1224 In addition to all of the scan methods discussed previously, Nmap
1225 offers options for specifying which ports are scanned and whether the
1226 scan order is randomized or sequential. By default, Nmap scans the most
1227 common 1,000 ports for each protocol.
1228 -p port ranges (Only scan specified ports)
1231 This option specifies which ports you want to scan and overrides
1232 the default. Individual port numbers are OK, as are ranges
1233 separated by a hyphen (e.g. 1-1023). The beginning and/or end
1234 values of a range may be omitted, causing Nmap to use 1 and 65535,
1235 respectively. So you can specify -p- to scan ports from 1 through
1236 65535. Scanning port zero is allowed if you specify it explicitly.
1237 For IP protocol scanning (-sO), this option specifies the protocol
1238 numbers you wish to scan for (0–255).
1239 When scanning a combination of protocols (e.g. TCP and UDP), you
1241 can specify a particular protocol by preceding the port numbers by
1242 T: for TCP, U: for UDP, S: for SCTP, or P: for IP Protocol. The
1243 qualifier lasts until you specify another qualifier. For example,
1244 the argument -p U:53,111,137,T:21-25,80,139,8080 would scan UDP
1245 ports 53, 111,and 137, as well as the listed TCP ports. Note that
1246 to scan both UDP and TCP, you have to specify -sU and at least one
1247 TCP scan type (such as -sS, -sF, or -sT). If no protocol qualifier
1248 is given, the port numbers are added to all protocol lists. Ports
1249 can also be specified by name according to what the port is
1250 referred to in the nmap-services. You can even use the wildcards *
1251 and ? with the names. For example, to scan FTP and all ports whose
1252 names begin with “http”, use -p ftp,http*. Be careful about shell
1253 expansions and quote the argument to -p if unsure.
1254 Ranges of ports can be surrounded by square brackets to indicate
1256 ports inside that range that appear in nmap-services. For example,
1257 the following will scan all ports in nmap-services equal to or
1258 below 1024: -p [-1024]. Be careful with shell expansions and quote
1259 the argument to -p if unsure.
1260 --exclude-ports port ranges (Exclude the specified ports from scanning)
1262 This option specifies which ports you do want Nmap to exclude from
1263 scanning. The port ranges are specified similar to -p. For IP
1264 protocol scanning (-sO), this option specifies the protocol numbers
1265 you wish to exclude (0–255).
1266 When ports are asked to be excluded, they are excluded from all
1268 types of scans (i.e. they will not be scanned under any
1269 circumstances). This also includes the discovery phase.
1270 -F (Fast (limited port) scan)
1272 Specifies that you wish to scan fewer ports than the default.
1273 Normally Nmap scans the most common 1,000 ports for each scanned
1274 protocol. With -F, this is reduced to 100.
1275 Nmap needs an nmap-services file with frequency information in
1277 order to know which ports are the most common. If port frequency
1278 information isn't available, perhaps because of the use of a custom
1279 nmap-services file, Nmap scans all named ports plus ports 1-1024.
1280 In that case, -F means to scan only ports that are named in the
1281 services file.
1282 -r (Don't randomize ports)
1284 By default, Nmap randomizes the scanned port order (except that
1285 certain commonly accessible ports are moved near the beginning for
1286 efficiency reasons). This randomization is normally desirable, but
1287 you can specify -r for sequential (sorted from lowest to highest)
1288 port scanning instead.
1289 --port-ratio ratio<decimal number between 0 and 1>
1291 Scans all ports in nmap-services file with a ratio greater than the
1292 one given. ratio must be between 0.0 and 1.0.
1293 --top-ports n
1295 Scans the n highest-ratio ports found in nmap-services file after
1296 excluding all ports specified by --exclude-ports. n must be 1 or
1297 greater.
1298
1300 Point Nmap at a remote machine and it might tell you that ports 25/tcp,
1301 80/tcp, and 53/udp are open. Using its nmap-services database of about
1302 2,200 well-known services, Nmap would report that those ports probably
1303 correspond to a mail server (SMTP), web server (HTTP), and name server
1304 (DNS) respectively. This lookup is usually accurate—the vast majority
1305 of daemons listening on TCP port 25 are, in fact, mail servers.
1306 However, you should not bet your security on this! People can and do
1307 run services on strange ports.
1308 Even if Nmap is right, and the hypothetical server above is running
1310 SMTP, HTTP, and DNS servers, that is not a lot of information. When
1311 doing vulnerability assessments (or even simple network inventories) of
1312 your companies or clients, you really want to know which mail and DNS
1313 servers and versions are running. Having an accurate version number
1314 helps dramatically in determining which exploits a server is vulnerable
1315 to. Version detection helps you obtain this information.
1316 After TCP and/or UDP ports are discovered using one of the other scan
1318 methods, version detection interrogates those ports to determine more
1319 about what is actually running. The nmap-service-probes database
1320 contains probes for querying various services and match expressions to
1321 recognize and parse responses. Nmap tries to determine the service
1322 protocol (e.g. FTP, SSH, Telnet, HTTP), the application name (e.g. ISC
1323 BIND, Apache httpd, Solaris telnetd), the version number, hostname,
1324 device type (e.g. printer, router), the OS family (e.g. Windows,
1325 Linux). When possible, Nmap also gets the Common Platform Enumeration
1326 (CPE) representation of this information. Sometimes miscellaneous
1327 details like whether an X server is open to connections, the SSH
1328 protocol version, or the KaZaA user name, are available. Of course,
1329 most services don't provide all of this information. If Nmap was
1330 compiled with OpenSSL support, it will connect to SSL servers to deduce
1331 the service listening behind that encryption layer. Some UDP ports are
1332 left in the open|filtered state after a UDP port scan is unable to
1333 determine whether the port is open or filtered. Version detection will
1334 try to elicit a response from these ports (just as it does with open
1335 ports), and change the state to open if it succeeds. open|filtered TCP
1336 ports are treated the same way. Note that the Nmap -A option enables
1337 version detection among other things. A paper documenting the
1338 workings, usage, and customization of version detection is available at
1339 https://nmap.org/book/vscan.html.
1340 When RPC services are discovered, the Nmap RPC grinder is automatically
1342 used to determine the RPC program and version numbers. It takes all the
1343 TCP/UDP ports detected as RPC and floods them with SunRPC program NULL
1344 commands in an attempt to determine whether they are RPC ports, and if
1345 so, what program and version number they serve up. Thus you can
1346 effectively obtain the same info as rpcinfo -p even if the target's
1347 portmapper is behind a firewall (or protected by TCP wrappers). Decoys
1348 do not currently work with RPC scan.
1349 When Nmap receives responses from a service but cannot match them to
1351 its database, it prints out a special fingerprint and a URL for you to
1352 submit if to if you know for sure what is running on the port. Please
1353 take a couple minutes to make the submission so that your find can
1354 benefit everyone. Thanks to these submissions, Nmap has about 6,500
1355 pattern matches for more than 650 protocols such as SMTP, FTP, HTTP,
1356 etc.
1357 Version detection is enabled and controlled with the following options:
1359 -sV (Version detection)
1361 Enables version detection, as discussed above. Alternatively, you
1362 can use -A, which enables version detection among other things.
1363 -sR is an alias for -sV. Prior to March 2011, it was used to active
1365 the RPC grinder separately from version detection, but now these
1366 options are always combined.
1367 --allports (Don't exclude any ports from version detection)
1369 By default, Nmap version detection skips TCP port 9100 because some
1370 printers simply print anything sent to that port, leading to dozens
1371 of pages of HTTP GET requests, binary SSL session requests, etc.
1372 This behavior can be changed by modifying or removing the Exclude
1373 directive in nmap-service-probes, or you can specify --allports to
1374 scan all ports regardless of any Exclude directive.
1375 --version-intensity intensity (Set version scan intensity)
1377 When performing a version scan (-sV), Nmap sends a series of
1378 probes, each of which is assigned a rarity value between one and
1379 nine. The lower-numbered probes are effective against a wide
1380 variety of common services, while the higher-numbered ones are
1381 rarely useful. The intensity level specifies which probes should be
1382 applied. The higher the number, the more likely it is the service
1383 will be correctly identified. However, high intensity scans take
1384 longer. The intensity must be between 0 and 9. The default is 7.
1385 When a probe is registered to the target port via the
1386 nmap-service-probes ports directive, that probe is tried regardless
1387 of intensity level. This ensures that the DNS probes will always be
1388 attempted against any open port 53, the SSL probe will be done
1389 against 443, etc.
1390 --version-light (Enable light mode)
1392 This is a convenience alias for --version-intensity 2. This light
1393 mode makes version scanning much faster, but it is slightly less
1394 likely to identify services.
1395 --version-all (Try every single probe)
1397 An alias for --version-intensity 9, ensuring that every single
1398 probe is attempted against each port.
1399 --version-trace (Trace version scan activity)
1401 This causes Nmap to print out extensive debugging info about what
1402 version scanning is doing. It is a subset of what you get with
1403 --packet-trace.
1404
1406 One of Nmap's best-known features is remote OS detection using TCP/IP
1407 stack fingerprinting. Nmap sends a series of TCP and UDP packets to the
1408 remote host and examines practically every bit in the responses. After
1409 performing dozens of tests such as TCP ISN sampling, TCP options
1410 support and ordering, IP ID sampling, and the initial window size
1411 check, Nmap compares the results to its nmap-os-db database of more
1412 than 2,600 known OS fingerprints and prints out the OS details if there
1413 is a match. Each fingerprint includes a freeform textual description of
1414 the OS, and a classification which provides the vendor name (e.g. Sun),
1415 underlying OS (e.g. Solaris), OS generation (e.g. 10), and device type
1416 (general purpose, router, switch, game console, etc). Most fingerprints
1417 also have a Common Platform Enumeration (CPE) representation, like
1418 cpe:/o:linux:linux_kernel:2.6.
1419 If Nmap is unable to guess the OS of a machine, and conditions are good
1421 (e.g. at least one open port and one closed port were found), Nmap will
1422 provide a URL you can use to submit the fingerprint if you know (for
1423 sure) the OS running on the machine. By doing this you contribute to
1424 the pool of operating systems known to Nmap and thus it will be more
1425 accurate for everyone.
1426 OS detection enables some other tests which make use of information
1428 that is gathered during the process anyway. One of these is TCP
1429 Sequence Predictability Classification. This measures approximately how
1430 hard it is to establish a forged TCP connection against the remote
1431 host. It is useful for exploiting source-IP based trust relationships
1432 (rlogin, firewall filters, etc) or for hiding the source of an attack.
1433 This sort of spoofing is rarely performed any more, but many machines
1434 are still vulnerable to it. The actual difficulty number is based on
1435 statistical sampling and may fluctuate. It is generally better to use
1436 the English classification such as “worthy challenge” or “trivial
1437 joke”. This is only reported in normal output in verbose (-v) mode.
1438 When verbose mode is enabled along with -O, IP ID sequence generation
1439 is also reported. Most machines are in the “incremental” class, which
1440 means that they increment the ID field in the IP header for each packet
1441 they send. This makes them vulnerable to several advanced information
1442 gathering and spoofing attacks.
1443 Another bit of extra information enabled by OS detection is a guess at
1445 a target's uptime. This uses the TCP timestamp option (RFC 1323[10]) to
1446 guess when a machine was last rebooted. The guess can be inaccurate due
1447 to the timestamp counter not being initialized to zero or the counter
1448 overflowing and wrapping around, so it is printed only in verbose mode.
1449 A paper documenting the workings, usage, and customization of OS
1451 detection is available at https://nmap.org/book/osdetect.html.
1452 OS detection is enabled and controlled with the following options:
1454 -O (Enable OS detection)
1456 Enables OS detection, as discussed above. Alternatively, you can
1457 use -A to enable OS detection along with other things.
1458 --osscan-limit (Limit OS detection to promising targets)
1460 OS detection is far more effective if at least one open and one
1461 closed TCP port are found. Set this option and Nmap will not even
1462 try OS detection against hosts that do not meet this criteria. This
1463 can save substantial time, particularly on -Pn scans against many
1464 hosts. It only matters when OS detection is requested with -O or
1465 -A.
1466 --osscan-guess; --fuzzy (Guess OS detection results)
1468 When Nmap is unable to detect a perfect OS match, it sometimes
1469 offers up near-matches as possibilities. The match has to be very
1470 close for Nmap to do this by default. Either of these (equivalent)
1471 options make Nmap guess more aggressively. Nmap will still tell you
1472 when an imperfect match is printed and display its confidence level
1473 (percentage) for each guess.
1474 --max-os-tries (Set the maximum number of OS detection tries against a
1476 target)
1477 When Nmap performs OS detection against a target and fails to find
1478 a perfect match, it usually repeats the attempt. By default, Nmap
1479 tries five times if conditions are favorable for OS fingerprint
1480 submission, and twice when conditions aren't so good. Specifying a
1481 lower --max-os-tries value (such as 1) speeds Nmap up, though you
1482 miss out on retries which could potentially identify the OS.
1483 Alternatively, a high value may be set to allow even more retries
1484 when conditions are favorable. This is rarely done, except to
1485 generate better fingerprints for submission and integration into
1486 the Nmap OS database.
1487
1489 The Nmap Scripting Engine (NSE) is one of Nmap's most powerful and
1490 flexible features. It allows users to write (and share) simple scripts
1491 (using the Lua programming language[11]
1492 ) to automate a wide variety of networking tasks. Those scripts are
1494 executed in parallel with the speed and efficiency you expect from
1495 Nmap. Users can rely on the growing and diverse set of scripts
1496 distributed with Nmap, or write their own to meet custom needs.
1497 Tasks we had in mind when creating the system include network
1499 discovery, more sophisticated version detection, vulnerability
1500 detection. NSE can even be used for vulnerability exploitation.
1501 To reflect those different uses and to simplify the choice of which
1503 scripts to run, each script contains a field associating it with one or
1504 more categories. Currently defined categories are auth, broadcast,
1505 default. discovery, dos, exploit, external, fuzzer, intrusive,
1506 malware, safe, version, and vuln. These are all described at
1507 https://nmap.org/book/nse-usage.html#nse-categories.
1508 Scripts are not run in a sandbox and thus could accidentally or
1510 maliciously damage your system or invade your privacy. Never run
1511 scripts from third parties unless you trust the authors or have
1512 carefully audited the scripts yourself.
1513 The Nmap Scripting Engine is described in detail at
1515 https://nmap.org/book/nse.html
1516 and is controlled by the following options:
1518 -sC
1520 Performs a script scan using the default set of scripts. It is
1521 equivalent to --script=default. Some of the scripts in this
1522 category are considered intrusive and should not be run against a
1523 target network without permission.
1524 --script filename|category|directory|expression[,...]
1526 Runs a script scan using the comma-separated list of filenames,
1527 script categories, and directories. Each element in the list may
1528 also be a Boolean expression describing a more complex set of
1529 scripts. Each element is interpreted first as an expression, then
1530 as a category, and finally as a file or directory name.
1531 There are two special features for advanced users only. One is to
1533 prefix script names and expressions with + to force them to run
1534 even if they normally wouldn't (e.g. the relevant service wasn't
1535 detected on the target port). The other is that the argument all
1536 may be used to specify every script in Nmap's database. Be cautious
1537 with this because NSE contains dangerous scripts such as exploits,
1538 brute force authentication crackers, and denial of service attacks.
1539 File and directory names may be relative or absolute. Absolute
1541 names are used directly. Relative paths are looked for in the
1542 scripts of each of the following places until found:
1543 --datadir
1544 $NMAPDIR
1545 ~/.nmap (not searched on Windows)
1546 HOME\AppData\Roaming\nmap (only on Windows)
1547 the directory containing the nmap executable
1548 the directory containing the nmap executable, followed by
1549 ../share/nmap
1550 NMAPDATADIR
1551 the current directory.
1552 When a directory name is given, Nmap loads every file in the
1554 directory whose name ends with .nse. All other files are ignored
1555 and directories are not searched recursively. When a filename is
1556 given, it does not have to have the .nse extension; it will be
1557 added automatically if necessary. Nmap scripts are stored in a
1558 scripts subdirectory of the Nmap data directory by default (see
1559 https://nmap.org/book/data-files.html).
1560 For efficiency, scripts are indexed in a database stored in
1562 scripts/script.db, which lists the category or categories in which
1563 each script belongs. When referring to scripts from script.db by
1564 name, you can use a shell-style ‘*’ wildcard.
1565 nmap --script "http-*"
1567 Loads all scripts whose name starts with http-, such as
1568 http-auth and http-open-proxy. The argument to --script had to
1569 be in quotes to protect the wildcard from the shell.
1570 More complicated script selection can be done using the and, or,
1572 and not operators to build Boolean expressions. The operators have
1573 the same precedence[12] as in Lua: not is the highest, followed by
1574 and and then or. You can alter precedence by using parentheses.
1575 Because expressions contain space characters it is necessary to
1576 quote them.
1577 nmap --script "not intrusive"
1579 Loads every script except for those in the intrusive category.
1580 nmap --script "default or safe"
1582 This is functionally equivalent to nmap --script
1583 "default,safe". It loads all scripts that are in the default
1584 category or the safe category or both.
1585 nmap --script "default and safe"
1587 Loads those scripts that are in both the default and safe
1588 categories.
1589 nmap --script "(default or safe or intrusive) and not http-*"
1591 Loads scripts in the default, safe, or intrusive categories,
1592 except for those whose names start with http-.
1593 --script-args n1=v1,n2={n3=v3},n4={v4,v5}
1595 Lets you provide arguments to NSE scripts. Arguments are a
1596 comma-separated list of name=value pairs. Names and values may be
1597 strings not containing whitespace or the characters ‘{’, ‘}’, ‘=’,
1598 or ‘,’. To include one of these characters in a string, enclose the
1599 string in single or double quotes. Within a quoted string, ‘\’
1600 escapes a quote. A backslash is only used to escape quotation marks
1601 in this special case; in all other cases a backslash is interpreted
1602 literally. Values may also be tables enclosed in {}, just as in
1603 Lua. A table may contain simple string values or more name-value
1604 pairs, including nested tables. Many scripts qualify their
1605 arguments with the script name, as in xmpp-info.server_name. You
1606 may use that full qualified version to affect just the specified
1607 script, or you may pass the unqualified version (server_name in
1608 this case) to affect all scripts using that argument name. A script
1609 will first check for its fully qualified argument name (the name
1610 specified in its documentation) before it accepts an unqualified
1611 argument name. A complex example of script arguments is
1612 --script-args
1613 'user=foo,pass=",{}=bar",whois={whodb=nofollow+ripe},xmpp-info.server_name=localhost'.
1614 The online NSE Documentation Portal at https://nmap.org/nsedoc/
1615 lists the arguments that each script accepts.
1616 --script-args-file filename
1618 Lets you load arguments to NSE scripts from a file. Any arguments
1619 on the command line supersede ones in the file. The file can be an
1620 absolute path, or a path relative to Nmap's usual search path
1621 (NMAPDIR, etc.) Arguments can be comma-separated or
1622 newline-separated, but otherwise follow the same rules as for
1623 --script-args, without requiring special quoting and escaping,
1624 since they are not parsed by the shell.
1625 --script-help filename|category|directory|expression|all[,...]
1627 Shows help about scripts. For each script matching the given
1628 specification, Nmap prints the script name, its categories, and its
1629 description. The specifications are the same as those accepted by
1630 --script; so for example if you want help about the ftp-anon
1631 script, you would run nmap --script-help ftp-anon. In addition to
1632 getting help for individual scripts, you can use this as a preview
1633 of what scripts will be run for a specification, for example with
1634 nmap --script-help default.
1635 --script-trace
1637 This option does what --packet-trace does, just one ISO layer
1638 higher. If this option is specified all incoming and outgoing
1639 communication performed by a script is printed. The displayed
1640 information includes the communication protocol, the source, the
1641 target and the transmitted data. If more than 5% of all transmitted
1642 data is not printable, then the trace output is in a hex dump
1643 format. Specifying --packet-trace enables script tracing too.
1644 --script-updatedb
1646 This option updates the script database found in scripts/script.db
1647 which is used by Nmap to determine the available default scripts
1648 and categories. It is only necessary to update the database if you
1649 have added or removed NSE scripts from the default scripts
1650 directory or if you have changed the categories of any script. This
1651 option is generally used by itself: nmap --script-updatedb.
1652
1654 One of my highest Nmap development priorities has always been
1655 performance. A default scan (nmap hostname) of a host on my local
1656 network takes a fifth of a second. That is barely enough time to blink,
1657 but adds up when you are scanning hundreds or thousands of hosts.
1658 Moreover, certain scan options such as UDP scanning and version
1659 detection can increase scan times substantially. So can certain
1660 firewall configurations, particularly response rate limiting. While
1661 Nmap utilizes parallelism and many advanced algorithms to accelerate
1662 these scans, the user has ultimate control over how Nmap runs. Expert
1663 users carefully craft Nmap commands to obtain only the information they
1664 care about while meeting their time constraints.
1665 Techniques for improving scan times include omitting non-critical
1667 tests, and upgrading to the latest version of Nmap (performance
1668 enhancements are made frequently). Optimizing timing parameters can
1669 also make a substantial difference. Those options are listed below.
1670 Some options accept a time parameter. This is specified in seconds by
1672 default, though you can append ‘ms’, ‘s’, ‘m’, or ‘h’ to the value to
1673 specify milliseconds, seconds, minutes, or hours. So the --host-timeout
1674 arguments 900000ms, 900, 900s, and 15m all do the same thing.
1675 --min-hostgroup numhosts; --max-hostgroup numhosts (Adjust parallel
1677 scan group sizes)
1678 Nmap has the ability to port scan or version scan multiple hosts in
1679 parallel. Nmap does this by dividing the target IP space into
1680 groups and then scanning one group at a time. In general, larger
1681 groups are more efficient. The downside is that host results can't
1682 be provided until the whole group is finished. So if Nmap started
1683 out with a group size of 50, the user would not receive any reports
1684 (except for the updates offered in verbose mode) until the first 50
1685 hosts are completed.
1686 By default, Nmap takes a compromise approach to this conflict. It
1688 starts out with a group size as low as five so the first results
1689 come quickly and then increases the groupsize to as high as 1024.
1690 The exact default numbers depend on the options given. For
1691 efficiency reasons, Nmap uses larger group sizes for UDP or
1692 few-port TCP scans.
1693 When a maximum group size is specified with --max-hostgroup, Nmap
1695 will never exceed that size. Specify a minimum size with
1696 --min-hostgroup and Nmap will try to keep group sizes above that
1697 level. Nmap may have to use smaller groups than you specify if
1698 there are not enough target hosts left on a given interface to
1699 fulfill the specified minimum. Both may be set to keep the group
1700 size within a specific range, though this is rarely desired.
1701 These options do not have an effect during the host discovery phase
1703 of a scan. This includes plain ping scans (-sn). Host discovery
1704 always works in large groups of hosts to improve speed and
1705 accuracy.
1706 The primary use of these options is to specify a large minimum
1708 group size so that the full scan runs more quickly. A common choice
1709 is 256 to scan a network in Class C sized chunks. For a scan with
1710 many ports, exceeding that number is unlikely to help much. For
1711 scans of just a few port numbers, host group sizes of 2048 or more
1712 may be helpful.
1713 --min-parallelism numprobes; --max-parallelism numprobes (Adjust probe
1715 parallelization)
1716 These options control the total number of probes that may be
1717 outstanding for a host group. They are used for port scanning and
1718 host discovery. By default, Nmap calculates an ever-changing ideal
1719 parallelism based on network performance. If packets are being
1720 dropped, Nmap slows down and allows fewer outstanding probes. The
1721 ideal probe number slowly rises as the network proves itself
1722 worthy. These options place minimum or maximum bounds on that
1723 variable. By default, the ideal parallelism can drop to one if the
1724 network proves unreliable and rise to several hundred in perfect
1725 conditions.
1726 The most common usage is to set --min-parallelism to a number
1728 higher than one to speed up scans of poorly performing hosts or
1729 networks. This is a risky option to play with, as setting it too
1730 high may affect accuracy. Setting this also reduces Nmap's ability
1731 to control parallelism dynamically based on network conditions. A
1732 value of 10 might be reasonable, though I only adjust this value as
1733 a last resort.
1734 The --max-parallelism option is sometimes set to one to prevent
1736 Nmap from sending more than one probe at a time to hosts. The
1737 --scan-delay option, discussed later, is another way to do this.
1738 --min-rtt-timeout time, --max-rtt-timeout time, --initial-rtt-timeout
1740 time (Adjust probe timeouts)
1741 Nmap maintains a running timeout value for determining how long it
1742 will wait for a probe response before giving up or retransmitting
1743 the probe. This is calculated based on the response times of
1744 previous probes.
1745 If the network latency shows itself to be significant and variable,
1747 this timeout can grow to several seconds. It also starts at a
1748 conservative (high) level and may stay that way for a while when
1749 Nmap scans unresponsive hosts.
1750 Specifying a lower --max-rtt-timeout and --initial-rtt-timeout than
1752 the defaults can cut scan times significantly. This is particularly
1753 true for pingless (-Pn) scans, and those against heavily filtered
1754 networks. Don't get too aggressive though. The scan can end up
1755 taking longer if you specify such a low value that many probes are
1756 timing out and retransmitting while the response is in transit.
1757 If all the hosts are on a local network, 100 milliseconds
1759 (--max-rtt-timeout 100ms) is a reasonable aggressive value. If
1760 routing is involved, ping a host on the network first with the ICMP
1761 ping utility, or with a custom packet crafter such as Nping that is
1762 more likely to get through a firewall. Look at the maximum round
1763 trip time out of ten packets or so. You might want to double that
1764 for the --initial-rtt-timeout and triple or quadruple it for the
1765 --max-rtt-timeout. I generally do not set the maximum RTT below
1766 100 ms, no matter what the ping times are. Nor do I exceed 1000 ms.
1767 --min-rtt-timeout is a rarely used option that could be useful when
1769 a network is so unreliable that even Nmap's default is too
1770 aggressive. Since Nmap only reduces the timeout down to the minimum
1771 when the network seems to be reliable, this need is unusual and
1772 should be reported as a bug to the nmap-dev mailing list.
1773 --max-retries numtries (Specify the maximum number of port scan probe
1775 retransmissions)
1776 When Nmap receives no response to a port scan probe, it could mean
1777 the port is filtered. Or maybe the probe or response was simply
1778 lost on the network. It is also possible that the target host has
1779 rate limiting enabled that temporarily blocked the response. So
1780 Nmap tries again by retransmitting the initial probe. If Nmap
1781 detects poor network reliability, it may try many more times before
1782 giving up on a port. While this benefits accuracy, it also
1783 lengthens scan times. When performance is critical, scans may be
1784 sped up by limiting the number of retransmissions allowed. You can
1785 even specify --max-retries 0 to prevent any retransmissions, though
1786 that is only recommended for situations such as informal surveys
1787 where occasional missed ports and hosts are acceptable.
1788 The default (with no -T template) is to allow ten retransmissions.
1790 If a network seems reliable and the target hosts aren't rate
1791 limiting, Nmap usually only does one retransmission. So most target
1792 scans aren't even affected by dropping --max-retries to a low value
1793 such as three. Such values can substantially speed scans of slow
1794 (rate limited) hosts. You usually lose some information when Nmap
1795 gives up on ports early, though that may be preferable to letting
1796 the --host-timeout expire and losing all information about the
1797 target.
1798 --host-timeout time (Give up on slow target hosts)
1800 Some hosts simply take a long time to scan. This may be due to
1801 poorly performing or unreliable networking hardware or software,
1802 packet rate limiting, or a restrictive firewall. The slowest few
1803 percent of the scanned hosts can eat up a majority of the scan
1804 time. Sometimes it is best to cut your losses and skip those hosts
1805 initially. Specify --host-timeout with the maximum amount of time
1806 you are willing to wait. For example, specify 30m to ensure that
1807 Nmap doesn't waste more than half an hour on a single host. Note
1808 that Nmap may be scanning other hosts at the same time during that
1809 half an hour, so it isn't a complete loss. A host that times out is
1810 skipped. No port table, OS detection, or version detection results
1811 are printed for that host.
1812 --script-timeout time
1814 While some scripts complete in fractions of a second, others can
1815 take hours or more depending on the nature of the script, arguments
1816 passed in, network and application conditions, and more. The
1817 --script-timeout option sets a ceiling on script execution time.
1818 Any script instance which exceeds that time will be terminated and
1819 no output will be shown. If debugging (-d) is enabled, Nmap will
1820 report on each timeout. For host and service scripts, a script
1821 instance only scans a single target host or port and the timeout
1822 period will be reset for the next instance.
1823 --scan-delay time; --max-scan-delay time (Adjust delay between probes)
1825 This option causes Nmap to wait at least the given amount of time
1826 between each probe it sends to a given host. This is particularly
1827 useful in the case of rate limiting. Solaris machines (among many
1828 others) will usually respond to UDP scan probe packets with only
1829 one ICMP message per second. Any more than that sent by Nmap will
1830 be wasteful. A --scan-delay of 1s will keep Nmap at that slow rate.
1831 Nmap tries to detect rate limiting and adjust the scan delay
1832 accordingly, but it doesn't hurt to specify it explicitly if you
1833 already know what rate works best.
1834 When Nmap adjusts the scan delay upward to cope with rate limiting,
1836 the scan slows down dramatically. The --max-scan-delay option
1837 specifies the largest delay that Nmap will allow. A low
1838 --max-scan-delay can speed up Nmap, but it is risky. Setting this
1839 value too low can lead to wasteful packet retransmissions and
1840 possible missed ports when the target implements strict rate
1841 limiting.
1842 Another use of --scan-delay is to evade threshold based intrusion
1844 detection and prevention systems (IDS/IPS).
1845 --min-rate number; --max-rate number (Directly control the scanning
1847 rate)
1848 Nmap's dynamic timing does a good job of finding an appropriate
1849 speed at which to scan. Sometimes, however, you may happen to know
1850 an appropriate scanning rate for a network, or you may have to
1851 guarantee that a scan will be finished by a certain time. Or
1852 perhaps you must keep Nmap from scanning too quickly. The
1853 --min-rate and --max-rate options are designed for these
1854 situations.
1855 When the --min-rate option is given Nmap will do its best to send
1857 packets as fast as or faster than the given rate. The argument is a
1858 positive real number representing a packet rate in packets per
1859 second. For example, specifying --min-rate 300 means that Nmap will
1860 try to keep the sending rate at or above 300 packets per second.
1861 Specifying a minimum rate does not keep Nmap from going faster if
1862 conditions warrant.
1863 Likewise, --max-rate limits a scan's sending rate to a given
1865 maximum. Use --max-rate 100, for example, to limit sending to 100
1866 packets per second on a fast network. Use --max-rate 0.1 for a slow
1867 scan of one packet every ten seconds. Use --min-rate and --max-rate
1868 together to keep the rate inside a certain range.
1869 These two options are global, affecting an entire scan, not
1871 individual hosts. They only affect port scans and host discovery
1872 scans. Other features like OS detection implement their own timing.
1873 There are two conditions when the actual scanning rate may fall
1875 below the requested minimum. The first is if the minimum is faster
1876 than the fastest rate at which Nmap can send, which is dependent on
1877 hardware. In this case Nmap will simply send packets as fast as
1878 possible, but be aware that such high rates are likely to cause a
1879 loss of accuracy. The second case is when Nmap has nothing to send,
1880 for example at the end of a scan when the last probes have been
1881 sent and Nmap is waiting for them to time out or be responded to.
1882 It's normal to see the scanning rate drop at the end of a scan or
1883 in between hostgroups. The sending rate may temporarily exceed the
1884 maximum to make up for unpredictable delays, but on average the
1885 rate will stay at or below the maximum.
1886 Specifying a minimum rate should be done with care. Scanning faster
1888 than a network can support may lead to a loss of accuracy. In some
1889 cases, using a faster rate can make a scan take longer than it
1890 would with a slower rate. This is because Nmap's
1891 adaptive retransmission algorithms will detect the network
1893 congestion caused by an excessive scanning rate and increase the
1894 number of retransmissions in order to improve accuracy. So even
1895 though packets are sent at a higher rate, more packets are sent
1896 overall. Cap the number of retransmissions with the --max-retries
1897 option if you need to set an upper limit on total scan time.
1898 --defeat-rst-ratelimit
1900 Many hosts have long used rate limiting to reduce the number of
1901 ICMP error messages (such as port-unreachable errors) they send.
1902 Some systems now apply similar rate limits to the RST (reset)
1903 packets they generate. This can slow Nmap down dramatically as it
1904 adjusts its timing to reflect those rate limits. You can tell Nmap
1905 to ignore those rate limits (for port scans such as SYN scan which
1906 don't treat non-responsive ports as open) by specifying
1907 --defeat-rst-ratelimit.
1908 Using this option can reduce accuracy, as some ports will appear
1910 non-responsive because Nmap didn't wait long enough for a
1911 rate-limited RST response. With a SYN scan, the non-response
1912 results in the port being labeled filtered rather than the closed
1913 state we see when RST packets are received. This option is useful
1914 when you only care about open ports, and distinguishing between
1915 closed and filtered ports isn't worth the extra time.
1916 --defeat-icmp-ratelimit
1918 Similar to --defeat-rst-ratelimit, the --defeat-icmp-ratelimit
1919 option trades accuracy for speed, increasing UDP scanning speed
1920 against hosts that rate-limit ICMP error messages. Because this
1921 option causes Nmap to not delay in order to receive the port
1922 unreachable messages, a non-responsive port will be labeled
1923 closed|filtered instead of the default open|filtered. This has the
1924 effect of only treating ports which actually respond via UDP as
1925 open. Since many UDP services do not respond in this way, the
1926 chance for inaccuracy is greater with this option than with
1927 --defeat-rst-ratelimit.
1928 --nsock-engine epoll|kqueue|poll|select
1930 Enforce use of a given nsock IO multiplexing engine. Only the
1931 select(2)-based fallback engine is guaranteed to be available on
1932 your system. Engines are named after the name of the IO management
1933 facility they leverage. Engines currently implemented are epoll,
1934 kqueue, poll, and select, but not all will be present on any
1935 platform. Use nmap -V to see which engines are supported.
1936 -T paranoid|sneaky|polite|normal|aggressive|insane (Set a timing
1938 template)
1939 While the fine-grained timing controls discussed in the previous
1940 section are powerful and effective, some people find them
1941 confusing. Moreover, choosing the appropriate values can sometimes
1942 take more time than the scan you are trying to optimize.
1943 Fortunately, Nmap offers a simpler approach, with six timing
1944 templates. You can specify them with the -T option and their number
1945 (0–5) or their name. The template names are paranoid (0),
1946 sneaky (1), polite (2), normal (3), aggressive (4), and insane (5).
1947 The first two are for IDS evasion. Polite mode slows down the scan
1948 to use less bandwidth and target machine resources. Normal mode is
1949 the default and so -T3 does nothing. Aggressive mode speeds scans
1950 up by making the assumption that you are on a reasonably fast and
1951 reliable network. Finally insane mode assumes that you are on an
1952 extraordinarily fast network or are willing to sacrifice some
1953 accuracy for speed.
1954 These templates allow the user to specify how aggressive they wish
1956 to be, while leaving Nmap to pick the exact timing values. The
1957 templates also make some minor speed adjustments for which
1958 fine-grained control options do not currently exist. For example,
1959 -T4 prohibits the dynamic scan delay from exceeding 10 ms for TCP
1960 ports and -T5 caps that value at 5 ms. Templates can be used in
1961 combination with fine-grained controls, and the fine-grained
1962 controls that you specify will take precedence over the timing
1963 template default for that parameter. I recommend using -T4 when
1964 scanning reasonably modern and reliable networks. Keep that option
1965 even when you add fine-grained controls so that you benefit from
1966 those extra minor optimizations that it enables.
1967 If you are on a decent broadband or ethernet connection, I would
1969 recommend always using -T4. Some people love -T5 though it is too
1970 aggressive for my taste. People sometimes specify -T2 because they
1971 think it is less likely to crash hosts or because they consider
1972 themselves to be polite in general. They often don't realize just
1973 how slow -T polite really is. Their scan may take ten times longer
1974 than a default scan. Machine crashes and bandwidth problems are
1975 rare with the default timing options (-T3) and so I normally
1976 recommend that for cautious scanners. Omitting version detection is
1977 far more effective than playing with timing values at reducing
1978 these problems.
1979 While -T0 and -T1 may be useful for avoiding IDS alerts, they will
1981 take an extraordinarily long time to scan thousands of machines or
1982 ports. For such a long scan, you may prefer to set the exact timing
1983 values you need rather than rely on the canned -T0 and -T1 values.
1984 The main effects of T0 are serializing the scan so only one port is
1986 scanned at a time, and waiting five minutes between sending each
1987 probe. T1 and T2 are similar but they only wait 15 seconds and 0.4
1988 seconds, respectively, between probes. T3 is Nmap's default
1989 behavior, which includes parallelization. -T4 does the equivalent
1990 of --max-rtt-timeout 1250ms --min-rtt-timeout 100ms
1991 --initial-rtt-timeout 500ms --max-retries 6 and sets the maximum
1992 TCP scan delay to 10 milliseconds. T5 does the equivalent of
1993 --max-rtt-timeout 300ms --min-rtt-timeout 50ms
1994 --initial-rtt-timeout 250ms --max-retries 2 --host-timeout 15m
1995 --script-timeout 10m as well as setting the maximum TCP scan delay
1996 to 5 ms.
1997
1999 Many Internet pioneers envisioned a global open network with a
2000 universal IP address space allowing virtual connections between any two
2001 nodes. This allows hosts to act as true peers, serving and retrieving
2002 information from each other. People could access all of their home
2003 systems from work, changing the climate control settings or unlocking
2004 the doors for early guests. This vision of universal connectivity has
2005 been stifled by address space shortages and security concerns. In the
2006 early 1990s, organizations began deploying firewalls for the express
2007 purpose of reducing connectivity. Huge networks were cordoned off from
2008 the unfiltered Internet by application proxies, network address
2009 translation, and packet filters. The unrestricted flow of information
2010 gave way to tight regulation of approved communication channels and the
2011 content that passes over them.
2012 Network obstructions such as firewalls can make mapping a network
2014 exceedingly difficult. It will not get any easier, as stifling casual
2015 reconnaissance is often a key goal of implementing the devices.
2016 Nevertheless, Nmap offers many features to help understand these
2017 complex networks, and to verify that filters are working as intended.
2018 It even supports mechanisms for bypassing poorly implemented defenses.
2019 One of the best methods of understanding your network security posture
2020 is to try to defeat it. Place yourself in the mind-set of an attacker,
2021 and deploy techniques from this section against your networks. Launch
2022 an FTP bounce scan, idle scan, fragmentation attack, or try to tunnel
2023 through one of your own proxies.
2024 In addition to restricting network activity, companies are increasingly
2026 monitoring traffic with intrusion detection systems (IDS). All of the
2027 major IDSs ship with rules designed to detect Nmap scans because scans
2028 are sometimes a precursor to attacks. Many of these products have
2029 recently morphed into intrusion prevention systems (IPS) that actively
2030 block traffic deemed malicious. Unfortunately for network
2031 administrators and IDS vendors, reliably detecting bad intentions by
2032 analyzing packet data is a tough problem. Attackers with patience,
2033 skill, and the help of certain Nmap options can usually pass by IDSs
2034 undetected. Meanwhile, administrators must cope with large numbers of
2035 false positive results where innocent activity is misdiagnosed and
2036 alerted on or blocked.
2037 Occasionally people suggest that Nmap should not offer features for
2039 evading firewall rules or sneaking past IDSs. They argue that these
2040 features are just as likely to be misused by attackers as used by
2041 administrators to enhance security. The problem with this logic is that
2042 these methods would still be used by attackers, who would just find
2043 other tools or patch the functionality into Nmap. Meanwhile,
2044 administrators would find it that much harder to do their jobs.
2045 Deploying only modern, patched FTP servers is a far more powerful
2046 defense than trying to prevent the distribution of tools implementing
2047 the FTP bounce attack.
2048 There is no magic bullet (or Nmap option) for detecting and subverting
2050 firewalls and IDS systems. It takes skill and experience. A tutorial is
2051 beyond the scope of this reference guide, which only lists the relevant
2052 options and describes what they do.
2053 -f (fragment packets); --mtu (using the specified MTU)
2055 The -f option causes the requested scan (including ping scans) to
2056 use tiny fragmented IP packets. The idea is to split up the TCP
2057 header over several packets to make it harder for packet filters,
2058 intrusion detection systems, and other annoyances to detect what
2059 you are doing. Be careful with this! Some programs have trouble
2060 handling these tiny packets. The old-school sniffer named Sniffit
2061 segmentation faulted immediately upon receiving the first fragment.
2062 Specify this option once, and Nmap splits the packets into eight
2063 bytes or less after the IP header. So a 20-byte TCP header would be
2064 split into three packets. Two with eight bytes of the TCP header,
2065 and one with the final four. Of course each fragment also has an IP
2066 header. Specify -f again to use 16 bytes per fragment (reducing the
2067 number of fragments). Or you can specify your own offset size with
2068 the --mtu option. Don't also specify -f if you use --mtu. The
2069 offset must be a multiple of eight. While fragmented packets won't
2070 get by packet filters and firewalls that queue all IP fragments,
2071 such as the CONFIG_IP_ALWAYS_DEFRAG option in the Linux kernel,
2072 some networks can't afford the performance hit this causes and thus
2073 leave it disabled. Others can't enable this because fragments may
2074 take different routes into their networks. Some source systems
2075 defragment outgoing packets in the kernel. Linux with the iptables
2076 connection tracking module is one such example. Do a scan while a
2077 sniffer such as Wireshark is running to ensure that sent packets
2078 are fragmented. If your host OS is causing problems, try the
2079 --send-eth option to bypass the IP layer and send raw ethernet
2080 frames.
2081 Fragmentation is only supported for Nmap's raw packet features,
2083 which includes TCP and UDP port scans (except connect scan and FTP
2084 bounce scan) and OS detection. Features such as version detection
2085 and the Nmap Scripting Engine generally don't support fragmentation
2086 because they rely on your host's TCP stack to communicate with
2087 target services.
2088 -D decoy1[,decoy2][,ME][,...] (Cloak a scan with decoys)
2090 Causes a decoy scan to be performed, which makes it appear to the
2091 remote host that the host(s) you specify as decoys are scanning the
2092 target network too. Thus their IDS might report 5–10 port scans
2093 from unique IP addresses, but they won't know which IP was scanning
2094 them and which were innocent decoys. While this can be defeated
2095 through router path tracing, response-dropping, and other active
2096 mechanisms, it is generally an effective technique for hiding your
2097 IP address.
2098 Separate each decoy host with commas, and you can optionally use ME
2100 as one of the decoys to represent the position for your real IP
2101 address. If you put ME in the sixth position or later, some common
2102 port scan detectors (such as Solar Designer's excellent Scanlogd)
2103 are unlikely to show your IP address at all. If you don't use ME,
2104 Nmap will put you in a random position. You can also use RND to
2105 generate a random, non-reserved IP address, or RND:number to
2106 generate number addresses.
2107 Note that the hosts you use as decoys should be up or you might
2109 accidentally SYN flood your targets. Also it will be pretty easy to
2110 determine which host is scanning if only one is actually up on the
2111 network. You might want to use IP addresses instead of names (so
2112 the decoy networks don't see you in their nameserver logs). Right
2113 now random IP address generation is only supported with IPv4
2114 Decoys are used both in the initial ping scan (using ICMP, SYN,
2116 ACK, or whatever) and during the actual port scanning phase. Decoys
2117 are also used during remote OS detection (-O). Decoys do not work
2118 with version detection or TCP connect scan. When a scan delay is in
2119 effect, the delay is enforced between each batch of spoofed probes,
2120 not between each individual probe. Because decoys are sent as a
2121 batch all at once, they may temporarily violate congestion control
2122 limits.
2123 It is worth noting that using too many decoys may slow your scan
2125 and potentially even make it less accurate. Also, some ISPs will
2126 filter out your spoofed packets, but many do not restrict spoofed
2127 IP packets at all.
2128 -S IP_Address (Spoof source address)
2130 In some circumstances, Nmap may not be able to determine your
2131 source address (Nmap will tell you if this is the case). In this
2132 situation, use -S with the IP address of the interface you wish to
2133 send packets through.
2134 Another possible use of this flag is to spoof the scan to make the
2136 targets think that someone else is scanning them. Imagine a company
2137 being repeatedly port scanned by a competitor! The -e option and
2138 -Pn are generally required for this sort of usage. Note that you
2139 usually won't receive reply packets back (they will be addressed to
2140 the IP you are spoofing), so Nmap won't produce useful reports.
2141 -e interface (Use specified interface)
2143 Tells Nmap what interface to send and receive packets on. Nmap
2144 should be able to detect this automatically, but it will tell you
2145 if it cannot.
2146 --source-port portnumber; -g portnumber (Spoof source port number)
2148 One surprisingly common misconfiguration is to trust traffic based
2149 only on the source port number. It is easy to understand how this
2150 comes about. An administrator will set up a shiny new firewall,
2151 only to be flooded with complaints from ungrateful users whose
2152 applications stopped working. In particular, DNS may be broken
2153 because the UDP DNS replies from external servers can no longer
2154 enter the network. FTP is another common example. In active FTP
2155 transfers, the remote server tries to establish a connection back
2156 to the client to transfer the requested file.
2157 Secure solutions to these problems exist, often in the form of
2159 application-level proxies or protocol-parsing firewall modules.
2160 Unfortunately there are also easier, insecure solutions. Noting
2161 that DNS replies come from port 53 and active FTP from port 20,
2162 many administrators have fallen into the trap of simply allowing
2163 incoming traffic from those ports. They often assume that no
2164 attacker would notice and exploit such firewall holes. In other
2165 cases, administrators consider this a short-term stop-gap measure
2166 until they can implement a more secure solution. Then they forget
2167 the security upgrade.
2168 Overworked network administrators are not the only ones to fall
2170 into this trap. Numerous products have shipped with these insecure
2171 rules. Even Microsoft has been guilty. The IPsec filters that
2172 shipped with Windows 2000 and Windows XP contain an implicit rule
2173 that allows all TCP or UDP traffic from port 88 (Kerberos). In
2174 another well-known case, versions of the Zone Alarm personal
2175 firewall up to 2.1.25 allowed any incoming UDP packets with the
2176 source port 53 (DNS) or 67 (DHCP).
2177 Nmap offers the -g and --source-port options (they are equivalent)
2179 to exploit these weaknesses. Simply provide a port number and Nmap
2180 will send packets from that port where possible. Most scanning
2181 operations that use raw sockets, including SYN and UDP scans,
2182 support the option completely. The option notably doesn't have an
2183 effect for any operations that use normal operating system sockets,
2184 including DNS requests, TCP connect scan, version detection, and
2185 script scanning. Setting the source port also doesn't work for OS
2186 detection, because Nmap must use different port numbers for certain
2187 OS detection tests to work properly.
2188 --data hex string (Append custom binary data to sent packets)
2190 This option lets you include binary data as payload in sent
2191 packets. hex string may be specified in any of the following
2192 formats: 0xAABBCCDDEEFF..., AABBCCDDEEFF... or
2193 \xAA\xBB\xCC\xDD\xEE\xFF.... Examples of use are --data 0xdeadbeef
2194 and --data \xCA\xFE\x09. Note that if you specify a number like
2195 0x00ff no byte-order conversion is performed. Make sure you specify
2196 the information in the byte order expected by the receiver.
2197 --data-string string (Append custom string to sent packets)
2199 This option lets you include a regular string as payload in sent
2200 packets. string can contain any string. However, note that some
2201 characters may depend on your system's locale and the receiver may
2202 not see the same information. Also, make sure you enclose the
2203 string in double quotes and escape any special characters from the
2204 shell. Examples: --data-string "Scan conducted by Security Ops,
2205 extension 7192" or --data-string "Ph34r my l33t skills". Keep in
2206 mind that nobody is likely to actually see any comments left by
2207 this option unless they are carefully monitoring the network with a
2208 sniffer or custom IDS rules.
2209 --data-length number (Append random data to sent packets)
2211 Normally Nmap sends minimalist packets containing only a header. So
2212 its TCP packets are generally 40 bytes and ICMP echo requests are
2213 just 28. Some UDP ports and IP protocols get a custom payload by
2214 default. This option tells Nmap to append the given number of
2215 random bytes to most of the packets it sends, and not to use any
2216 protocol-specific payloads. (Use --data-length 0 for no random or
2217 protocol-specific payloads. OS detection (-O) packets are not
2218 affected because accuracy there requires probe consistency, but
2219 most pinging and portscan packets support this. It slows things
2220 down a little, but can make a scan slightly less conspicuous.
2221 --ip-options S|R [route]|L [route]|T|U ... ; --ip-options hex string
2223 (Send packets with specified ip options)
2224 The IP protocol[13] offers several options which may be placed in
2225 packet headers. Unlike the ubiquitous TCP options, IP options are
2226 rarely seen due to practicality and security concerns. In fact,
2227 many Internet routers block the most dangerous options such as
2228 source routing. Yet options can still be useful in some cases for
2229 determining and manipulating the network route to target machines.
2230 For example, you may be able to use the record route option to
2231 determine a path to a target even when more traditional
2232 traceroute-style approaches fail. Or if your packets are being
2233 dropped by a certain firewall, you may be able to specify a
2234 different route with the strict or loose source routing options.
2235 The most powerful way to specify IP options is to simply pass in
2237 values as the argument to --ip-options. Precede each hex number
2238 with \x then the two digits. You may repeat certain characters by
2239 following them with an asterisk and then the number of times you
2240 wish them to repeat. For example, \x01\x07\x04\x00*36\x01 is a hex
2241 string containing 36 NUL bytes.
2242 Nmap also offers a shortcut mechanism for specifying options.
2244 Simply pass the letter R, T, or U to request record-route,
2245 record-timestamp, or both options together, respectively. Loose or
2246 strict source routing may be specified with an L or S followed by a
2247 space and then a space-separated list of IP addresses.
2248 If you wish to see the options in packets sent and received,
2250 specify --packet-trace. For more information and examples of using
2251 IP options with Nmap, see http://seclists.org/nmap-dev/2006/q3/52.
2252 --ttl value (Set IP time-to-live field)
2254 Sets the IPv4 time-to-live field in sent packets to the given
2255 value.
2256 --randomize-hosts (Randomize target host order)
2258 Tells Nmap to shuffle each group of up to 16384 hosts before it
2259 scans them. This can make the scans less obvious to various network
2260 monitoring systems, especially when you combine it with slow timing
2261 options. If you want to randomize over larger group sizes, increase
2262 PING_GROUP_SZ in nmap.h and recompile. An alternative solution is
2263 to generate the target IP list with a list scan (-sL -n -oN
2264 filename), randomize it with a Perl script, then provide the whole
2265 list to Nmap with -iL.
2266 --spoof-mac MAC address, prefix, or vendor name (Spoof MAC address)
2268 Asks Nmap to use the given MAC address
2269 for all of the raw ethernet frames it sends. This option implies
2271 --send-eth to ensure that Nmap actually sends ethernet-level
2272 packets. The MAC given can take several formats. If it is simply
2273 the number 0, Nmap chooses a completely random MAC address for the
2274 session. If the given string is an even number of hex digits (with
2275 the pairs optionally separated by a colon), Nmap will use those as
2276 the MAC. If fewer than 12 hex digits are provided, Nmap fills in
2277 the remainder of the six bytes with random values. If the argument
2278 isn't a zero or hex string, Nmap looks through nmap-mac-prefixes to
2279 find a vendor name containing the given string (it is case
2280 insensitive). If a match is found, Nmap uses the vendor's OUI
2281 (three-byte prefix) and fills out the remaining three bytes
2282 randomly. Valid --spoof-mac argument examples are Apple, 0,
2283 01:02:03:04:05:06, deadbeefcafe, 0020F2, and Cisco. This option
2284 only affects raw packet scans such as SYN scan or OS detection, not
2285 connection-oriented features such as version detection or the Nmap
2286 Scripting Engine.
2287 --proxies Comma-separated list of proxy URLs (Relay TCP connections
2289 through a chain of proxies)
2290 Asks Nmap to establish TCP connections with a final target through
2291 supplied chain of one or more HTTP or SOCKS4
2292 proxies. Proxies can help hide the true source of a scan or evade
2294 certain firewall restrictions, but they can hamper scan performance
2295 by increasing latency. Users may need to adjust Nmap timeouts and
2296 other scan parameters accordingly. In particular, a lower
2297 --max-parallelism may help because some proxies refuse to handle as
2298 many concurrent connections as Nmap opens by default.
2299 This option takes a list of proxies as argument, expressed as URLs
2301 in the format proto://host:port. Use commas to separate node URLs
2302 in a chain. No authentication is supported yet. Valid protocols are
2303 HTTP and SOCKS4.
2304 Warning: this feature is still under development and has
2306 limitations. It is implemented within the nsock library and thus
2307 has no effect on the ping, port scanning and OS discovery phases of
2308 a scan. Only NSE and version scan benefit from this option so far—
2309 other features may disclose your true address. SSL connections are
2310 not yet supported, nor is proxy-side DNS resolution (hostnames are
2311 always resolved by Nmap).
2312 --badsum (Send packets with bogus TCP/UDP checksums)
2314 Asks Nmap to use an invalid TCP, UDP or SCTP checksum for packets
2315 sent to target hosts. Since virtually all host IP stacks properly
2316 drop these packets, any responses received are likely coming from a
2317 firewall or IDS that didn't bother to verify the checksum. For more
2318 details on this technique, see https://nmap.org/p60-12.html
2319 --adler32 (Use deprecated Adler32 instead of CRC32C for SCTP checksums)
2321 Asks Nmap to use the deprecated Adler32 algorithm for calculating
2322 the SCTP checksum. If --adler32 is not given, CRC-32C (Castagnoli)
2323 is used. RFC 2960[14] originally defined Adler32 as checksum
2324 algorithm for SCTP; RFC 4960[7] later redefined the SCTP checksums
2325 to use CRC-32C. Current SCTP implementations should be using
2326 CRC-32C, but in order to elicit responses from old, legacy SCTP
2327 implementations, it may be preferable to use Adler32.
2328
2330 Any security tool is only as useful as the output it generates. Complex
2331 tests and algorithms are of little value if they aren't presented in an
2332 organized and comprehensible fashion. Given the number of ways Nmap is
2333 used by people and other software, no single format can please
2334 everyone. So Nmap offers several formats, including the interactive
2335 mode for humans to read directly and XML for easy parsing by software.
2336 In addition to offering different output formats, Nmap provides options
2338 for controlling the verbosity of output as well as debugging messages.
2339 Output types may be sent to standard output or to named files, which
2340 Nmap can append to or clobber. Output files may also be used to resume
2341 aborted scans.
2342 Nmap makes output available in five different formats. The default is
2344 called interactive output, and it is sent to standard output (stdout).
2345 There is also normal output, which is similar to interactive except
2346 that it displays less runtime information and warnings since it is
2347 expected to be analyzed after the scan completes rather than
2348 interactively.
2349 XML output is one of the most important output types, as it can be
2351 converted to HTML, easily parsed by programs such as Nmap graphical
2352 user interfaces, or imported into databases.
2353 The two remaining output types are the simple grepable output which
2355 includes most information for a target host on a single line, and
2356 sCRiPt KiDDi3 0utPUt for users who consider themselves |<-r4d.
2357 While interactive output is the default and has no associated
2359 command-line options, the other four format options use the same
2360 syntax. They take one argument, which is the filename that results
2361 should be stored in. Multiple formats may be specified, but each format
2362 may only be specified once. For example, you may wish to save normal
2363 output for your own review while saving XML of the same scan for
2364 programmatic analysis. You might do this with the options -oX
2365 myscan.xml -oN myscan.nmap. While this chapter uses the simple names
2366 like myscan.xml for brevity, more descriptive names are generally
2367 recommended. The names chosen are a matter of personal preference,
2368 though I use long ones that incorporate the scan date and a word or two
2369 describing the scan, placed in a directory named after the company I'm
2370 scanning.
2371 While these options save results to files, Nmap still prints
2373 interactive output to stdout as usual. For example, the command nmap
2374 -oX myscan.xml target prints XML to myscan.xml and fills standard
2375 output with the same interactive results it would have printed if -oX
2376 wasn't specified at all. You can change this by passing a hyphen
2377 character as the argument to one of the format types. This causes Nmap
2378 to deactivate interactive output, and instead print results in the
2379 format you specified to the standard output stream. So the command nmap
2380 -oX - target will send only XML output to stdout. Serious errors may
2381 still be printed to the normal error stream, stderr.
2382 Unlike some Nmap arguments, the space between the logfile option flag
2384 (such as -oX) and the filename or hyphen is mandatory. If you omit the
2385 flags and give arguments such as -oG- or -oXscan.xml, a backwards
2386 compatibility feature of Nmap will cause the creation of normal format
2387 output files named G- and Xscan.xml respectively.
2388 All of these arguments support strftime-like conversions in the
2390 filename. %H, %M, %S, %m, %d, %y, and %Y are all exactly the same as
2391 in strftime. %T is the same as %H%M%S, %R is the same as %H%M, and %D
2392 is the same as %m%d%y. A % followed by any other character just yields
2393 that character (%% gives you a percent symbol). So -oX 'scan-%T-%D.xml'
2394 will use an XML file with a name in the form of scan-144840-121307.xml.
2395 Nmap also offers options to control scan verbosity and to append to
2397 output files rather than clobbering them. All of these options are
2398 described below.
2399 Nmap Output Formats
2401 -oN filespec (normal output)
2403 Requests that normal output be directed to the given filename. As
2404 discussed above, this differs slightly from interactive output.
2405 -oX filespec (XML output)
2407 Requests that XML output be directed to the given filename. Nmap
2408 includes a document type definition (DTD) which allows XML parsers
2409 to validate Nmap XML output. While it is primarily intended for
2410 programmatic use, it can also help humans interpret Nmap XML
2411 output. The DTD defines the legal elements of the format, and often
2412 enumerates the attributes and values they can take on. The latest
2413 version is always available from
2414 https://svn.nmap.org/nmap/docs/nmap.dtd.
2415 XML offers a stable format that is easily parsed by software. Free
2417 XML parsers are available for all major computer languages,
2418 including C/C++, Perl, Python, and Java. People have even written
2419 bindings for most of these languages to handle Nmap output and
2420 execution specifically. Examples are Nmap::Scanner[15] and
2421 Nmap::Parser[16] in Perl CPAN. In almost all cases that a
2422 non-trivial application interfaces with Nmap, XML is the preferred
2423 format.
2424 The XML output references an XSL stylesheet which can be used to
2426 format the results as HTML. The easiest way to use this is simply
2427 to load the XML output in a web browser such as Firefox or IE. By
2428 default, this will only work on the machine you ran Nmap on (or a
2429 similarly configured one) due to the hard-coded nmap.xsl filesystem
2430 path. Use the --webxml or --stylesheet options to create portable
2431 XML files that render as HTML on any web-connected machine.
2432 -oS filespec (ScRipT KIdd|3 oUTpuT)
2434 Script kiddie output is like interactive output, except that it is
2435 post-processed to better suit the l33t HaXXorZ who previously
2436 looked down on Nmap due to its consistent capitalization and
2437 spelling. Humor impaired people should note that this option is
2438 making fun of the script kiddies before flaming me for supposedly
2439 “helping them”.
2440 -oG filespec (grepable output)
2442 This output format is covered last because it is deprecated. The
2443 XML output format is far more powerful, and is nearly as convenient
2444 for experienced users. XML is a standard for which dozens of
2445 excellent parsers are available, while grepable output is my own
2446 simple hack. XML is extensible to support new Nmap features as they
2447 are released, while I often must omit those features from grepable
2448 output for lack of a place to put them.
2449 Nevertheless, grepable output is still quite popular. It is a
2451 simple format that lists each host on one line and can be trivially
2452 searched and parsed with standard Unix tools such as grep, awk,
2453 cut, sed, diff, and Perl. Even I usually use it for one-off tests
2454 done at the command line. Finding all the hosts with the SSH port
2455 open or that are running Solaris takes only a simple grep to
2456 identify the hosts, piped to an awk or cut command to print the
2457 desired fields.
2458 Grepable output consists of comments (lines starting with a pound
2460 (#)) and target lines. A target line includes a combination of six
2461 labeled fields, separated by tabs and followed with a colon. The
2462 fields are Host, Ports, Protocols, Ignored State, OS, Seq Index, IP
2463 ID, and Status.
2464 The most important of these fields is generally Ports, which gives
2466 details on each interesting port. It is a comma separated list of
2467 port entries. Each port entry represents one interesting port, and
2468 takes the form of seven slash (/) separated subfields. Those
2469 subfields are: Port number, State, Protocol, Owner, Service, SunRPC
2470 info, and Version info.
2471 As with XML output, this man page does not allow for documenting
2473 the entire format. A more detailed look at the Nmap grepable output
2474 format is available from
2475 https://nmap.org/book/output-formats-grepable-output.html.
2476 -oA basename (Output to all formats)
2478 As a convenience, you may specify -oA basename to store scan
2479 results in normal, XML, and grepable formats at once. They are
2480 stored in basename.nmap, basename.xml, and basename.gnmap,
2481 respectively. As with most programs, you can prefix the filenames
2482 with a directory path, such as ~/nmaplogs/foocorp/ on Unix or
2483 c:\hacking\sco on Windows.
2484 Verbosity and debugging options
2486 -v (Increase verbosity level), -vlevel (Set verbosity level)
2488 Increases the verbosity level, causing Nmap to print more
2489 information about the scan in progress. Open ports are shown as
2490 they are found and completion time estimates are provided when Nmap
2491 thinks a scan will take more than a few minutes. Use it twice or
2492 more for even greater verbosity: -vv, or give a verbosity level
2493 directly, for example -v3.
2494 Most changes only affect interactive output, and some also affect
2496 normal and script kiddie output. The other output types are meant
2497 to be processed by machines, so Nmap can give substantial detail by
2498 default in those formats without fatiguing a human user. However,
2499 there are a few changes in other modes where output size can be
2500 reduced substantially by omitting some detail. For example, a
2501 comment line in the grepable output that provides a list of all
2502 ports scanned is only printed in verbose mode because it can be
2503 quite long.
2504 -d (Increase debugging level), -dlevel (Set debugging level)
2506 When even verbose mode doesn't provide sufficient data for you,
2507 debugging is available to flood you with much more! As with the
2508 verbosity option (-v), debugging is enabled with a command-line
2509 flag (-d) and the debug level can be increased by specifying it
2510 multiple times, as in -dd, or by setting a level directly. For
2511 example, -d9 sets level nine. That is the highest effective level
2512 and will produce thousands of lines unless you run a very simple
2513 scan with very few ports and targets.
2514 Debugging output is useful when a bug is suspected in Nmap, or if
2516 you are simply confused as to what Nmap is doing and why. As this
2517 feature is mostly intended for developers, debug lines aren't
2518 always self-explanatory. You may get something like: Timeout vals:
2519 srtt: -1 rttvar: -1 to: 1000000 delta 14987 ==> srtt: 14987 rttvar:
2520 14987 to: 100000. If you don't understand a line, your only
2521 recourses are to ignore it, look it up in the source code, or
2522 request help from the development list (nmap-dev). Some lines are
2523 self explanatory, but the messages become more obscure as the debug
2524 level is increased.
2525 --reason (Host and port state reasons)
2527 Shows the reason each port is set to a specific state and the
2528 reason each host is up or down. This option displays the type of
2529 the packet that determined a port or hosts state. For example, A
2530 RST packet from a closed port or an echo reply from an alive host.
2531 The information Nmap can provide is determined by the type of scan
2532 or ping. The SYN scan and SYN ping (-sS and -PS) are very detailed,
2533 but the TCP connect scan (-sT) is limited by the implementation of
2534 the connect system call. This feature is automatically enabled by
2535 the debug option (-d) and the results are stored in XML log files
2536 even if this option is not specified.
2537 --stats-every time (Print periodic timing stats)
2539 Periodically prints a timing status message after each interval of
2540 time. The time is a specification of the kind described in the
2541 section called “TIMING AND PERFORMANCE”; so for example, use
2542 --stats-every 10s to get a status update every 10 seconds. Updates
2543 are printed to interactive output (the screen) and XML output.
2544 --packet-trace (Trace packets and data sent and received)
2546 Causes Nmap to print a summary of every packet sent or received.
2547 This is often used for debugging, but is also a valuable way for
2548 new users to understand exactly what Nmap is doing under the
2549 covers. To avoid printing thousands of lines, you may want to
2550 specify a limited number of ports to scan, such as -p20-30. If you
2551 only care about the goings on of the version detection subsystem,
2552 use --version-trace instead. If you only care about script tracing,
2553 specify --script-trace. With --packet-trace, you get all of the
2554 above.
2555 --open (Show only open (or possibly open) ports)
2557 Sometimes you only care about ports you can actually connect to
2558 (open ones), and don't want results cluttered with closed,
2559 filtered, and closed|filtered ports. Output customization is
2560 normally done after the scan using tools such as grep, awk, and
2561 Perl, but this feature was added due to overwhelming requests.
2562 Specify --open to only see hosts with at least one open,
2563 open|filtered, or unfiltered port, and only see ports in those
2564 states. These three states are treated just as they normally are,
2565 which means that open|filtered and unfiltered may be condensed into
2566 counts if there are an overwhelming number of them.
2567 --iflist (List interfaces and routes)
2569 Prints the interface list and system routes as detected by Nmap.
2570 This is useful for debugging routing problems or device
2571 mischaracterization (such as Nmap treating a PPP connection as
2572 ethernet).
2573 Miscellaneous output options
2575 --append-output (Append to rather than clobber output files)
2577 When you specify a filename to an output format flag such as -oX or
2578 -oN, that file is overwritten by default. If you prefer to keep the
2579 existing content of the file and append the new results, specify
2580 the --append-output option. All output filenames specified in that
2581 Nmap execution will then be appended to rather than clobbered. This
2582 doesn't work well for XML (-oX) scan data as the resultant file
2583 generally won't parse properly until you fix it up by hand.
2584 --resume filename (Resume aborted scan)
2586 Some extensive Nmap runs take a very long time—on the order of
2587 days. Such scans don't always run to completion. Restrictions may
2588 prevent Nmap from being run during working hours, the network could
2589 go down, the machine Nmap is running on might suffer a planned or
2590 unplanned reboot, or Nmap itself could crash. The administrator
2591 running Nmap could cancel it for any other reason as well, by
2592 pressing ctrl-C. Restarting the whole scan from the beginning may
2593 be undesirable. Fortunately, if normal (-oN) or grepable (-oG) logs
2594 were kept, the user can ask Nmap to resume scanning with the target
2595 it was working on when execution ceased. Simply specify the
2596 --resume option and pass the normal/grepable output file as its
2597 argument. No other arguments are permitted, as Nmap parses the
2598 output file to use the same ones specified previously. Simply call
2599 Nmap as nmap --resume logfilename. Nmap will append new results to
2600 the data files specified in the previous execution. Resumption does
2601 not support the XML output format because combining the two runs
2602 into one valid XML file would be difficult.
2603 --stylesheet path or URL (Set XSL stylesheet to transform XML output)
2605 Nmap ships with an XSL stylesheet named nmap.xsl for viewing or
2606 translating XML output to HTML. The XML output includes an
2607 xml-stylesheet directive which points to nmap.xml where it was
2608 initially installed by Nmap. Run the XML file through an XSLT
2609 processor such as xsltproc[17] to produce an HTML file. Directly
2610 opening the XML file in a browser no longer works well because
2611 modern browsers limit the locations a stylesheet may be loaded
2612 from. If you wish to use a different stylesheet, specify it as the
2613 argument to --stylesheet. You must pass the full pathname or URL.
2614 One common invocation is --stylesheet
2615 https://nmap.org/svn/docs/nmap.xsl. This tells an XSLT processor to
2616 load the latest version of the stylesheet from Nmap.Org. The
2617 --webxml option does the same thing with less typing and
2618 memorization. Loading the XSL from Nmap.Org makes it easier to view
2619 results on a machine that doesn't have Nmap (and thus nmap.xsl)
2620 installed. So the URL is often more useful, but the local
2621 filesystem location of nmap.xsl is used by default for privacy
2622 reasons.
2623 --webxml (Load stylesheet from Nmap.Org)
2625 This is a convenience option, nothing more than an alias for
2626 --stylesheet https://nmap.org/svn/docs/nmap.xsl.
2627 --no-stylesheet (Omit XSL stylesheet declaration from XML)
2629 Specify this option to prevent Nmap from associating any XSL
2630 stylesheet with its XML output. The xml-stylesheet directive is
2631 omitted.
2632
2634 This section describes some important (and not-so-important) options
2635 that don't really fit anywhere else.
2636 -6 (Enable IPv6 scanning)
2638 Nmap has IPv6 support for its most popular features. Ping scanning,
2639 port scanning, version detection, and the Nmap Scripting Engine all
2640 support IPv6. The command syntax is the same as usual except that
2641 you also add the -6 option. Of course, you must use IPv6 syntax if
2642 you specify an address rather than a hostname. An address might
2643 look like 3ffe:7501:4819:2000:210:f3ff:fe03:14d0, so hostnames are
2644 recommended. The output looks the same as usual, with the IPv6
2645 address on the “interesting ports” line being the only IPv6
2646 giveaway.
2647 While IPv6 hasn't exactly taken the world by storm, it gets
2649 significant use in some (usually Asian) countries and most modern
2650 operating systems support it. To use Nmap with IPv6, both the
2651 source and target of your scan must be configured for IPv6. If your
2652 ISP (like most of them) does not allocate IPv6 addresses to you,
2653 free tunnel brokers are widely available and work fine with Nmap. I
2654 use the free IPv6 tunnel broker service at
2655 http://www.tunnelbroker.net. Other tunnel brokers are listed at
2656 Wikipedia[18]. 6to4 tunnels are another popular, free approach.
2657 On Windows, raw-socket IPv6 scans are supported only on ethernet
2659 devices (not tunnels), and only on Windows Vista and later. Use the
2660 --unprivileged option in other situations.
2661 -A (Aggressive scan options)
2663 This option enables additional advanced and aggressive options.
2664 Presently this enables OS detection (-O), version scanning (-sV),
2665 script scanning (-sC) and traceroute (--traceroute). More features
2666 may be added in the future. The point is to enable a comprehensive
2667 set of scan options without people having to remember a large set
2668 of flags. However, because script scanning with the default set is
2669 considered intrusive, you should not use -A against target networks
2670 without permission. This option only enables features, and not
2671 timing options (such as -T4) or verbosity options (-v) that you
2672 might want as well. Options which require privileges (e.g. root
2673 access) such as OS detection and traceroute will only be enabled if
2674 those privileges are available.
2675 --datadir directoryname (Specify custom Nmap data file location)
2677 Nmap obtains some special data at runtime in files named
2678 nmap-service-probes, nmap-services, nmap-protocols, nmap-rpc,
2679 nmap-mac-prefixes, and nmap-os-db. If the location of any of these
2680 files has been specified (using the --servicedb or --versiondb
2681 options), that location is used for that file. After that, Nmap
2682 searches these files in the directory specified with the --datadir
2683 option (if any). Any files not found there, are searched for in the
2684 directory specified by the NMAPDIR environment variable. Next comes
2685 ~/.nmap for real and effective UIDs; or on Windows,
2686 HOME\AppData\Roaming\nmap (where HOME is the user's home directory,
2687 like C:\Users\user). This is followed by the location of the nmap
2688 executable and the same location with ../share/nmap appended. Then
2689 a compiled-in location such as /usr/local/share/nmap or
2690 /usr/share/nmap.
2691 --servicedb services file (Specify custom services file)
2693 Asks Nmap to use the specified services file rather than the
2694 nmap-services data file that comes with Nmap. Using this option
2695 also causes a fast scan (-F) to be used. See the description for
2696 --datadir for more information on Nmap's data files.
2697 --versiondb service probes file (Specify custom service probes file)
2699 Asks Nmap to use the specified service probes file rather than the
2700 nmap-service-probes data file that comes with Nmap. See the
2701 description for --datadir for more information on Nmap's data
2702 files.
2703 --send-eth (Use raw ethernet sending)
2705 Asks Nmap to send packets at the raw ethernet (data link) layer
2706 rather than the higher IP (network) layer. By default, Nmap chooses
2707 the one which is generally best for the platform it is running on.
2708 Raw sockets (IP layer) are generally most efficient for Unix
2709 machines, while ethernet frames are required for Windows operation
2710 since Microsoft disabled raw socket support. Nmap still uses raw IP
2711 packets on Unix despite this option when there is no other choice
2712 (such as non-ethernet connections).
2713 --send-ip (Send at raw IP level)
2715 Asks Nmap to send packets via raw IP sockets rather than sending
2716 lower level ethernet frames. It is the complement to the --send-eth
2717 option discussed previously.
2718 --privileged (Assume that the user is fully privileged)
2720 Tells Nmap to simply assume that it is privileged enough to perform
2721 raw socket sends, packet sniffing, and similar operations that
2722 usually require root privileges on Unix systems. By default Nmap
2723 quits if such operations are requested but geteuid is not zero.
2724 --privileged is useful with Linux kernel capabilities and similar
2725 systems that may be configured to allow unprivileged users to
2726 perform raw-packet scans. Be sure to provide this option flag
2727 before any flags for options that require privileges (SYN scan, OS
2728 detection, etc.). The NMAP_PRIVILEGED environment variable may be
2729 set as an equivalent alternative to --privileged.
2730 --unprivileged (Assume that the user lacks raw socket privileges)
2732 This option is the opposite of --privileged. It tells Nmap to treat
2733 the user as lacking network raw socket and sniffing privileges.
2734 This is useful for testing, debugging, or when the raw network
2735 functionality of your operating system is somehow broken. The
2736 NMAP_UNPRIVILEGED environment variable may be set as an equivalent
2737 alternative to --unprivileged.
2738 --release-memory (Release memory before quitting)
2740 This option is only useful for memory-leak debugging. It causes
2741 Nmap to release allocated memory just before it quits so that
2742 actual memory leaks are easier to spot. Normally Nmap skips this as
2743 the OS does this anyway upon process termination.
2744 -V; --version (Print version number)
2746 Prints the Nmap version number and exits.
2747 -h; --help (Print help summary page)
2749 Prints a short help screen with the most common command flags.
2750 Running Nmap without any arguments does the same thing.
2751
2753 During the execution of Nmap, all key presses are captured. This allows
2754 you to interact with the program without aborting and restarting it.
2755 Certain special keys will change options, while any other keys will
2756 print out a status message telling you about the scan. The convention
2757 is that lowercase letters increase the amount of printing, and
2758 uppercase letters decrease the printing. You may also press ‘?’ for
2759 help.
2760 v / V
2762 Increase / decrease the verbosity level
2763 d / D
2765 Increase / decrease the debugging Level
2766 p / P
2768 Turn on / off packet tracing
2769 ?
2771 Print a runtime interaction help screen
2772 Anything else
2774 Print out a status message like this:
2775 Stats: 0:00:07 elapsed; 20 hosts completed (1 up), 1 undergoing Service Scan
2777 Service scan Timing: About 33.33% done; ETC: 20:57 (0:00:12 remaining)
2778
2780 Here are some Nmap usage examples, from the simple and routine to a
2781 little more complex and esoteric. Some actual IP addresses and domain
2782 names are used to make things more concrete. In their place you should
2783 substitute addresses/names from your own network. While I don't think
2784 port scanning other networks is or should be illegal, some network
2785 administrators don't appreciate unsolicited scanning of their networks
2786 and may complain. Getting permission first is the best approach.
2787 For testing purposes, you have permission to scan the host
2789 scanme.nmap.org. This permission only includes scanning via Nmap and
2790 not testing exploits or denial of service attacks. To conserve
2791 bandwidth, please do not initiate more than a dozen scans against that
2792 host per day. If this free scanning target service is abused, it will
2793 be taken down and Nmap will report Failed to resolve given hostname/IP:
2794 scanme.nmap.org. These permissions also apply to the hosts
2795 scanme2.nmap.org, scanme3.nmap.org, and so on, though those hosts do
2796 not currently exist.
2797 nmap -v scanme.nmap.org
2799 This option scans all reserved TCP ports on the machine scanme.nmap.org
2801 . The -v option enables verbose mode.
2802 nmap -sS -O scanme.nmap.org/24
2804 Launches a stealth SYN scan against each machine that is up out of the
2807 256 IPs on the class C sized network where Scanme resides. It also
2808 tries to determine what operating system is running on each host that
2809 is up and running. This requires root privileges because of the SYN
2810 scan and OS detection.
2811 nmap -sV -p 22,53,110,143,4564 198.116.0-255.1-127
2813 Launches host enumeration and a TCP scan at the first half of each of
2815 the 255 possible eight-bit subnets in the 198.116 class B address
2816 space. This tests whether the systems run SSH, DNS, POP3, or IMAP on
2817 their standard ports, or anything on port 4564. For any of these ports
2818 found open, version detection is used to determine what application is
2819 running.
2820 nmap -v -iR 100000 -Pn -p 80
2822 Asks Nmap to choose 100,000 hosts at random and scan them for web
2825 servers (port 80). Host enumeration is disabled with -Pn since first
2826 sending a couple probes to determine whether a host is up is wasteful
2827 when you are only probing one port on each target host anyway.
2828 nmap -Pn -p80 -oX logs/pb-port80scan.xml -oG logs/pb-port80scan.gnmap
2830 216.163.128.20/20
2831 This scans 4096 IPs for any web servers (without pinging them) and
2834 saves the output in grepable and XML formats.
2835
2837 While this reference guide details all material Nmap options, it can't
2838 fully demonstrate how to apply those features to quickly solve
2839 real-world tasks. For that, we released Nmap Network Scanning: The
2840 Official Nmap Project Guide to Network Discovery and Security Scanning.
2841 Topics include subverting firewalls and intrusion detection systems,
2842 optimizing Nmap performance, and automating common networking tasks
2843 with the Nmap Scripting Engine. Hints and instructions are provided for
2844 common Nmap tasks such as taking network inventory, penetration
2845 testing, detecting rogue wireless access points, and quashing network
2846 worm outbreaks. Examples and diagrams show actual communication on the
2847 wire. More than half of the book is available free online. See
2848 https://nmap.org/book for more information.
2849
2851 Like its author, Nmap isn't perfect. But you can help make it better by
2852 sending bug reports or even writing patches. If Nmap doesn't behave the
2853 way you expect, first upgrade to the latest version available from
2854 https://nmap.org. If the problem persists, do some research to
2855 determine whether it has already been discovered and addressed. Try
2856 searching for the problem or error message on Google since that
2857 aggregates so many forums. If nothing comes of this, create an Issue on
2858 our tracker (http://issues.nmap.org) and/or mail a bug report to
2859 <dev@nmap.org>. If you subscribe to the nmap-dev list before posting,
2860 your message will bypass moderation and get through more quickly.
2861 Subscribe at https://nmap.org/mailman/listinfo/dev. Please include
2862 everything you have learned about the problem, as well as what version
2863 of Nmap you are using and what operating system version it is running
2864 on. Other suggestions for improving Nmap may be sent to the Nmap dev
2865 mailing list as well.
2866 If you are able to write a patch improving Nmap or fixing a bug, that
2868 is even better! Instructions for submitting patches or git pull
2869 requests are available from
2870 https://github.com/nmap/nmap/blob/master/CONTRIBUTING.md
2871 Particularly sensitive issues such as a security reports may be sent
2873 directly to Nmap's author Fyodor directly at <fyodor@nmap.org>. All
2874 other reports and comments should use the dev list or issue tracker
2875 instead because more people read, follow, and respond to those.
2876
2878 Gordon “Fyodor” Lyon <fyodor@nmap.org> wrote and released Nmap in 1997.
2879 Since then, hundreds of people have made valuable contributions, as
2880 detailed in the CHANGELOG file distributed with Nmap and also available
2881 from https://nmap.org/changelog.html. David Fifield and Daniel Miller
2882 deserve special recognition for their enormous multi-year
2883 contributions!
2884
2886 Nmap Copyright and Licensing
2887 The Nmap Security Scanner is (C) 1996–2018 Insecure.Com LLC ("The Nmap
2888 Project"). Nmap is also a registered trademark of the Nmap Project.
2889 This program free software; you may redistribute and/or modify it under
2890 the terms of the GNU General Public License as published by the Free
2891 Software Foundation; Version 2 (“GPL”), BUT ONLY WITH ALL OF THE
2892 CLARIFICATIONS AND EXCEPTIONS DESCRIBED HEREIN. This guarantees your
2893 right to use, modify, and redistribute this software under certain
2894 conditions. If you wish to embed Nmap technology into proprietary
2895 software, we sell alternative licenses (contact <sales@nmap.com>).
2896 Dozens of software vendors already license Nmap technology such as host
2897 discovery, port scanning, OS detection, version detection, and the Nmap
2898 Scripting Engine.
2899 Note that the GPL places important restrictions on “derivative works”,
2901 yet it does not provide a detailed definition of that term. To avoid
2902 misunderstandings, we interpret that term as broadly as copyright law
2903 allows. For example, we consider an application to constitute a
2904 derivative work for the purpose of this license if it does any of the
2905 following with any software or content covered by this license
2906 (“Covered Software”):
2907 · Integrates source code from Covered Software.
2909 · Reads or includes copyrighted data files, such as Nmap's nmap-os-db
2911 or nmap-service-probes.
2912 · Is designed specifically to execute Covered Software and parse the
2914 results (as opposed to typical shell or execution-menu apps, which
2915 will execute anything you tell them to).
2916 · Includes Covered Software in a proprietary executable installer.
2918 The installers produced by InstallShield are an example of this.
2919 Including Nmap with other software in compressed or archival form
2920 does not trigger this provision, provided appropriate open source
2921 decompression or de-archiving software is widely available for no
2922 charge. For the purposes of this license, an installer is
2923 considered to include Covered Software even if it actually
2924 retrieves a copy of Covered Software from another source during
2925 runtime (such as by downloading it from the Internet).
2926 · Links (statically or dynamically) to a library which does any of
2928 the above.
2929 · Executes a helper program, module, or script to do any of the
2931 above.
2932 This list is not exclusive, but is meant to clarify our interpretation
2934 of derived works with some common examples. Other people may interpret
2935 the plain GPL differently, so we consider this a special exception to
2936 the GPL that we apply to Covered Software. Works which meet any of
2937 these conditions must conform to all of the terms of this license,
2938 particularly including the GPL Section 3 requirements of providing
2939 source code and allowing free redistribution of the work as a whole.
2940 As another special exception to the GPL terms, the Nmap Project grants
2942 permission to link the code of this program with any version of the
2943 OpenSSL library which is distributed under a license identical to that
2944 listed in the included docs/licenses/OpenSSL.txt file, and distribute
2945 linked combinations including the two.
2946 The Nmap Project has permission to redistribute Npcap, a packet
2948 capturing driver and library for the Microsoft Windows platform. Npcap
2949 is a separate work with it's own license rather than this Nmap license.
2950 Since the Npcap license does not permit redistribution without special
2951 permission, our Nmap Windows binary packages which contain Npcap may
2952 not be redistributed without special permission.
2953 Any redistribution of Covered Software, including any derived works,
2955 must obey and carry forward all of the terms of this license, including
2956 obeying all GPL rules and restrictions. For example, source code of the
2957 whole work must be provided and free redistribution must be allowed.
2958 All GPL references to "this License", are to be treated as including
2959 the terms and conditions of this license text as well.
2960 Because this license imposes special exceptions to the GPL, Covered
2962 Work may not be combined (even as part of a larger work) with plain GPL
2963 software. The terms, conditions, and exceptions of this license must be
2964 included as well. This license is incompatible with some other open
2965 source licenses as well. In some cases we can relicense portions of
2966 Nmap or grant special permissions to use it in other open source
2967 software. Please contact fyodor@nmap.org with any such requests.
2968 Similarly, we don't incorporate incompatible open source software into
2969 Covered Software without special permission from the copyright holders.
2970 If you have any questions about the licensing restrictions on using
2972 Nmap in other works, we are happy to help. As mentioned above, we also
2973 offer an alternative license to integrate Nmap into proprietary
2974 applications and appliances. These contracts have been sold to dozens
2975 of software vendors, and generally include a perpetual license as well
2976 as providing support and updates. They also fund the continued
2977 development of Nmap. Please email <sales@nmap.com> for further
2978 information.
2979 If you have received a written license agreement or contract for
2981 Covered Software stating terms other than these, you may choose to use
2982 and redistribute Covered Software under those terms instead of these.
2983 Creative Commons License for this Nmap Guide
2985 This Nmap Reference Guide is (C) 2005–2018 Insecure.Com LLC. It is
2986 hereby placed under version 3.0 of the Creative Commons Attribution
2987 License[19]. This allows you redistribute and modify the work as you
2988 desire, as long as you credit the original source. Alternatively, you
2989 may choose to treat this document as falling under the same license as
2990 Nmap itself (discussed previously).
2991 Source Code Availability and Community Contributions
2993 Source is provided to this software because we believe users have a
2994 right to know exactly what a program is going to do before they run it.
2995 This also allows you to audit the software for security holes.
2996 Source code also allows you to port Nmap to new platforms, fix bugs,
2998 and add new features. You are highly encouraged to send your changes to
2999 <dev@nmap.org> for possible incorporation into the main distribution.
3000 By sending these changes to Fyodor or one of the Insecure.Org
3001 development mailing lists, it is assumed that you are offering the Nmap
3002 Project the unlimited, non-exclusive right to reuse, modify, and
3003 relicense the code. Nmap will always be available open source, but this
3004 is important because the inability to relicense code has caused
3005 devastating problems for other Free Software projects (such as KDE and
3006 NASM). We also occasionally relicense the code to third parties as
3007 discussed above. If you wish to specify special license conditions of
3008 your contributions, just say so when you send them.
3009 No Warranty
3011 This program is distributed in the hope that it will be useful, but
3012 WITHOUT ANY WARRANTY; without even the implied warranty of
3013 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
3014 General Public License v2.0 for more details at
3015 http://www.gnu.org/licenses/gpl-2.0.html, or in the COPYING file
3016 included with Nmap.
3017 It should also be noted that Nmap has occasionally been known to crash
3019 poorly written applications, TCP/IP stacks, and even operating systems.
3020 While this is extremely rare, it is important to keep in mind. Nmap
3021 should never be run against mission critical systems unless you are
3022 prepared to suffer downtime. We acknowledge here that Nmap may crash
3023 your systems or networks and we disclaim all liability for any damage
3024 or problems Nmap could cause.
3025 Inappropriate Usage
3027 Because of the slight risk of crashes and because a few black hats like
3028 to use Nmap for reconnaissance prior to attacking systems, there are
3029 administrators who become upset and may complain when their system is
3030 scanned. Thus, it is often advisable to request permission before doing
3031 even a light scan of a network.
3032 Nmap should never be installed with special privileges (e.g. suid
3034 root). That would open up a major security vulnerability as other
3035 users on the system (or attackers) could use it for privilege
3036 escalation.
3037 Third-Party Software and Funding Notices
3039 This product includes software developed by the Apache Software
3040 Foundation[20]. A modified version of the Libpcap portable packet
3041 capture library[21] is distributed along with Nmap. The Windows version
3042 of Nmap utilizes the Libpcap-derived Ncap library[22] instead. Regular
3043 expression support is provided by the PCRE library[23], which is
3044 open-source software, written by Philip Hazel. Certain raw networking
3045 functions use the Libdnet[24] networking library, which was written by
3046 Dug Song. A modified version is distributed with Nmap. Nmap can
3047 optionally link with the OpenSSL cryptography toolkit[25] for SSL
3048 version detection support. The Nmap Scripting Engine uses an embedded
3049 version of the Lua programming language[26]. The Liblinear linear
3050 classification library[27] is used for our IPv6 OS detection machine
3051 learning techniques[28].
3052 All of the third-party software described in this paragraph is freely
3054 redistributable under BSD-style software licenses.
3055 Binary packages for Windows and Mac OS X include support libraries
3057 necessary to run Zenmap and Ndiff with Python and PyGTK. (Unix
3058 platforms commonly make these libraries easy to install, so they are
3059 not part of the packages.) A listing of these support libraries and
3060 their licenses is included in the LICENSES files.
3061 This software was supported in part through the Google Summer of
3063 Code[29] and the DARPA CINDER program[30] (DARPA-BAA-10-84).
3064 United States Export Control
3066 Nmap only uses encryption when compiled with the optional OpenSSL
3067 support and linked with OpenSSL. When compiled without OpenSSL support,
3068 the Nmap Project believes that Nmap is not subject to U.S. Export
3069 Administration Regulations (EAR)[31] export control. As such, there is
3070 no applicable ECCN (export control classification number) and
3071 exportation does not require any special license, permit, or other
3072 governmental authorization.
3073 When compiled with OpenSSL support or distributed as source code, the
3075 Nmap Project believes that Nmap falls under U.S. ECCN 5D002[32]
3076 (“Information Security Software”). We distribute Nmap under the TSU
3077 exception for publicly available encryption software defined in EAR
3078 740.13(e)[33].
3079
3081 1. Nmap Network Scanning: The Official Nmap Project Guide to Network
3082 Discovery and Security Scanning
3083 https://nmap.org/book/
3084 2. RFC 1122
3086 http://www.rfc-editor.org/rfc/rfc1122.txt
3087 3. RFC 792
3089 http://www.rfc-editor.org/rfc/rfc792.txt
3090 4. RFC 950
3092 http://www.rfc-editor.org/rfc/rfc950.txt
3093 5. RFC 1918
3095 http://www.rfc-editor.org/rfc/rfc1918.txt
3096 6. UDP
3098 http://www.rfc-editor.org/rfc/rfc768.txt
3099 7. SCTP
3101 http://www.rfc-editor.org/rfc/rfc4960.txt
3102 8. TCP RFC
3104 http://www.rfc-editor.org/rfc/rfc793.txt
3105 9. RFC 959
3107 http://www.rfc-editor.org/rfc/rfc959.txt
3108 10. RFC 1323
3110 http://www.rfc-editor.org/rfc/rfc1323.txt
3111 11. Lua programming language
3113 http://lua.org
3114 12. precedence
3116 http://www.lua.org/manual/5.1/manual.html#2.5.3
3117 13. IP protocol
3119 http://www.rfc-editor.org/rfc/rfc791.txt
3120 14. RFC 2960
3122 http://www.rfc-editor.org/rfc/rfc2960.txt
3123 15. Nmap::Scanner
3125 http://sourceforge.net/projects/nmap-scanner/
3126 16. Nmap::Parser
3128 http://nmapparser.wordpress.com/
3129 17. xsltproc
3131 http://xmlsoft.org/XSLT/
3132 18. listed at Wikipedia
3134 http://en.wikipedia.org/wiki/List_of_IPv6_tunnel_brokers
3135 19. Creative Commons Attribution License
3137 http://creativecommons.org/licenses/by/3.0/
3138 20. Apache Software Foundation
3140 http://www.apache.org
3141 21. Libpcap portable packet capture library
3143 http://www.tcpdump.org
3144 22. Ncap library
3146 https://npcap.org
3147 23. PCRE library
3149 http://www.pcre.org
3150 24. Libdnet
3152 http://libdnet.sourceforge.net
3153 25. OpenSSL cryptography toolkit
3155 http://www.openssl.org
3156 26. Lua programming language
3158 http://www.lua.org
3159 27. Liblinear linear classification library
3161 http://www.csie.ntu.edu.tw/~cjlin/liblinear/
3162 28. IPv6 OS detection machine learning techniques
3164 https://nmap.org/book/osdetect-guess.html#osdetect-guess-ipv6
3165 29. Google Summer of Code
3167 https://nmap.org/soc/
3168 30. DARPA CINDER program
3170 https://www.fbo.gov/index?s=opportunity&mode=form&id=585e02a51f77af5cb3c9e06b9cc82c48&tab=core&_cview=1
3171 31. Export Administration Regulations (EAR)
3173 http://www.access.gpo.gov/bis/ear/ear_data.html
3174 32. 5D002
3176 https://www.bis.doc.gov/index.php/documents/regulations-docs/federal-register-notices/federal-register-2014/951-ccl5-pt2/file
3177 33. EAR 740.13(e)
3179 http://www.access.gpo.gov/bis/ear/pdf/740.pdf
3180Nmap 09/28/2018 NMAP(1)