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 7.92 ( 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 --noninteractive: Disable runtime interactions via keyboard
194 --stylesheet <path/URL>: XSL stylesheet to transform XML output to HTML
195 --webxml: Reference stylesheet from Nmap.Org for more portable XML
196 --no-stylesheet: Prevent associating of XSL stylesheet w/XML output
197 MISC:
198 -6: Enable IPv6 scanning
199 -A: Enable OS detection, version detection, script scanning, and traceroute
200 --datadir <dirname>: Specify custom Nmap data file location
201 --send-eth/--send-ip: Send using raw ethernet frames or IP packets
202 --privileged: Assume that the user is fully privileged
203 --unprivileged: Assume the user lacks raw socket privileges
204 -V: Print version number
205 -h: Print this help summary page.
206 EXAMPLES:
207 nmap -v -A scanme.nmap.org
208 nmap -v -sn 192.168.0.0/16 10.0.0.0/8
209 nmap -v -iR 10000 -Pn -p 80
210 SEE THE MAN PAGE (https://nmap.org/book/man.html) FOR MORE OPTIONS AND EXAMPLES
211
213 Everything on the Nmap command-line that isn't an option (or option
214 argument) is treated as a target host specification. The simplest case
215 is to specify a target IP address or hostname for scanning.
216 When a hostname is given as a target, it is resolved via the Domain
218 Name System (DNS) to determine the IP address to scan. If the name
219 resolves to more than one IP address, only the first one will be
220 scanned. To make Nmap scan all the resolved addresses instead of only
221 the first one, use the --resolve-all option.
222 Sometimes you wish to scan a whole network of adjacent hosts. For this,
224 Nmap supports CIDR-style addressing. You can append /numbits to an IP
225 address or hostname and Nmap will scan every IP address for which the
226 first numbits are the same as for the reference IP or hostname given.
227 For example, 192.168.10.0/24 would scan the 256 hosts between
228 192.168.10.0 (binary: 11000000 10101000 00001010 00000000) and
229 192.168.10.255 (binary: 11000000 10101000 00001010 11111111),
230 inclusive. 192.168.10.40/24 would scan exactly the same targets. Given
231 that the host scanme.nmap.org is at the IP address 64.13.134.52, the
232 specification scanme.nmap.org/16 would scan the 65,536 IP addresses
233 between 64.13.0.0 and 64.13.255.255. The smallest allowed value is /0,
234 which targets the whole Internet. The largest value for IPv4 is /32,
235 which scans just the named host or IP address because all address bits
236 are fixed. The largest value for IPv6 is /128, which does the same
237 thing.
238 CIDR notation is short but not always flexible enough. For example, you
240 might want to scan 192.168.0.0/16 but skip any IPs ending with .0 or
241 .255 because they may be used as subnet network and broadcast
242 addresses. Nmap supports this through octet range addressing. Rather
243 than specify a normal IP address, you can specify a comma-separated
244 list of numbers or ranges for each octet. For example,
245 192.168.0-255.1-254 will skip all addresses in the range that end in .0
246 or .255, and 192.168.3-5,7.1 will scan the four addresses 192.168.3.1,
247 192.168.4.1, 192.168.5.1, and 192.168.7.1. Either side of a range may
248 be omitted; the default values are 0 on the left and 255 on the right.
249 Using - by itself is the same as 0-255, but remember to use 0- in the
250 first octet so the target specification doesn't look like a
251 command-line option. Ranges need not be limited to the final octets:
252 the specifier 0-255.0-255.13.37 will perform an Internet-wide scan for
253 all IP addresses ending in 13.37. This sort of broad sampling can be
254 useful for Internet surveys and research.
255 IPv6 addresses can be specified by their fully qualified IPv6 address
257 or hostname or with CIDR notation for subnets. Octet ranges aren't yet
258 supported for IPv6.
259 IPv6 addresses with non-global scope need to have a zone ID suffix. On
261 Unix systems, this is a percent sign followed by an interface name; a
262 complete address might be fe80::a8bb:ccff:fedd:eeff%eth0. On Windows,
263 use an interface index number in place of an interface name:
264 fe80::a8bb:ccff:fedd:eeff%1. You can see a list of interface indexes by
265 running the command netsh.exe interface ipv6 show interface.
266 Nmap accepts multiple host specifications on the command line, and they
268 don't need to be the same type. The command nmap scanme.nmap.org
269 192.168.0.0/8 10.0.0,1,3-7.- does what you would expect.
270 While targets are usually specified on the command lines, the following
272 options are also available to control target selection:
273 -iL inputfilename (Input from list)
275 Reads target specifications from inputfilename. Passing a huge list
276 of hosts is often awkward on the command line, yet it is a common
277 desire. For example, your DHCP server might export a list of 10,000
278 current leases that you wish to scan. Or maybe you want to scan all
279 IP addresses except for those to locate hosts using unauthorized
280 static IP addresses. Simply generate the list of hosts to scan and
281 pass that filename to Nmap as an argument to the -iL option.
282 Entries can be in any of the formats accepted by Nmap on the
283 command line (IP address, hostname, CIDR, IPv6, or octet ranges).
284 Each entry must be separated by one or more spaces, tabs, or
285 newlines. You can specify a hyphen (-) as the filename if you want
286 Nmap to read hosts from standard input rather than an actual file.
287 The input file may contain comments that start with # and extend to
289 the end of the line.
290 -iR num hosts (Choose random targets)
292 For Internet-wide surveys and other research, you may want to
293 choose targets at random. The num hosts argument tells Nmap how
294 many IPs to generate. Undesirable IPs such as those in certain
295 private, multicast, or unallocated address ranges are automatically
296 skipped. The argument 0 can be specified for a never-ending scan.
297 Keep in mind that some network administrators bristle at
298 unauthorized scans of their networks and may complain. Use this
299 option at your own risk! If you find yourself really bored one
300 rainy afternoon, try the command nmap -Pn -sS -p 80 -iR 0 --open to
301 locate random web servers for browsing.
302 --exclude host1[,host2[,...]] (Exclude hosts/networks)
304 Specifies a comma-separated list of targets to be excluded from the
305 scan even if they are part of the overall network range you
306 specify. The list you pass in uses normal Nmap syntax, so it can
307 include hostnames, CIDR netblocks, octet ranges, etc. This can be
308 useful when the network you wish to scan includes untouchable
309 mission-critical servers, systems that are known to react adversely
310 to port scans, or subnets administered by other people.
311 --excludefile exclude_file (Exclude list from file)
313 This offers the same functionality as the --exclude option, except
314 that the excluded targets are provided in a newline-, space-, or
315 tab-delimited exclude_file rather than on the command line.
316 The exclude file may contain comments that start with # and extend
318 to the end of the line.
319
321 One of the very first steps in any network reconnaissance mission is to
322 reduce a (sometimes huge) set of IP ranges into a list of active or
323 interesting hosts. Scanning every port of every single IP address is
324 slow and usually unnecessary. Of course what makes a host interesting
325 depends greatly on the scan purposes. Network administrators may only
326 be interested in hosts running a certain service, while security
327 auditors may care about every single device with an IP address. An
328 administrator may be comfortable using just an ICMP ping to locate
329 hosts on his internal network, while an external penetration tester may
330 use a diverse set of dozens of probes in an attempt to evade firewall
331 restrictions.
332 Because host discovery needs are so diverse, Nmap offers a wide variety
334 of options for customizing the techniques used. Host discovery is
335 sometimes called ping scan, but it goes well beyond the simple ICMP
336 echo request packets associated with the ubiquitous ping tool. Users
337 can skip the discovery step entirely with a list scan (-sL) or by
338 disabling host discovery (-Pn), or engage the network with arbitrary
339 combinations of multi-port TCP SYN/ACK, UDP, SCTP INIT and ICMP probes.
340 The goal of these probes is to solicit responses which demonstrate that
341 an IP address is actually active (is being used by a host or network
342 device). On many networks, only a small percentage of IP addresses are
343 active at any given time. This is particularly common with private
344 address space such as 10.0.0.0/8. That network has 16 million IPs, but
345 I have seen it used by companies with less than a thousand machines.
346 Host discovery can find those machines in a sparsely allocated sea of
347 IP addresses.
348 If no host discovery options are given, Nmap sends an ICMP echo
350 request, a TCP SYN packet to port 443, a TCP ACK packet to port 80, and
351 an ICMP timestamp request. (For IPv6, the ICMP timestamp request is
352 omitted because it is not part of ICMPv6.) These defaults are
353 equivalent to the -PE -PS443 -PA80 -PP options. The exceptions to this
354 are the ARP (for IPv4) and Neighbor Discovery (for IPv6) scans which
355 are used for any targets on a local ethernet network. For unprivileged
356 Unix shell users, the default probes are a SYN packet to ports 80 and
357 443 using the connect system call. This host discovery is often
358 sufficient when scanning local networks, but a more comprehensive set
359 of discovery probes is recommended for security auditing.
360 The -P* options (which select ping types) can be combined. You can
362 increase your odds of penetrating strict firewalls by sending many
363 probe types using different TCP ports/flags and ICMP codes. Also note
364 that ARP/Neighbor Discovery is done by default against targets on a
365 local Ethernet network even if you specify other -P* options, because
366 it is almost always faster and more effective.
367 By default, Nmap does host discovery and then performs a port scan
369 against each host it determines is online. This is true even if you
370 specify non-default host discovery types such as UDP probes (-PU). Read
371 about the -sn option to learn how to perform only host discovery, or
372 use -Pn to skip host discovery and port scan all target addresses. The
373 following options control host discovery:
374 -sL (List Scan)
376 The list scan is a degenerate form of host discovery that simply
377 lists each host of the network(s) specified, without sending any
378 packets to the target hosts. By default, Nmap still does
379 reverse-DNS resolution on the hosts to learn their names. It is
380 often surprising how much useful information simple hostnames give
381 out. For example, fw.chi is the name of one company's Chicago
382 firewall.
383 Nmap also reports the total number of IP addresses at the end. The
385 list scan is a good sanity check to ensure that you have proper IP
386 addresses for your targets. If the hosts sport domain names you do
387 not recognize, it is worth investigating further to prevent
388 scanning the wrong company's network.
389 Since the idea is to simply print a list of target hosts, options
391 for higher level functionality such as port scanning, OS detection,
392 or host discovery cannot be combined with this. If you wish to
393 disable host discovery while still performing such higher level
394 functionality, read up on the -Pn (skip host discovery) option.
395 -sn (No port scan)
397 This option tells Nmap not to do a port scan after host discovery,
398 and only print out the available hosts that responded to the host
399 discovery probes. This is often known as a “ping scan”, but you can
400 also request that traceroute and NSE host scripts be run. This is
401 by default one step more intrusive than the list scan, and can
402 often be used for the same purposes. It allows light reconnaissance
403 of a target network without attracting much attention. Knowing how
404 many hosts are up is more valuable to attackers than the list
405 provided by list scan of every single IP and host name.
406 Systems administrators often find this option valuable as well. It
408 can easily be used to count available machines on a network or
409 monitor server availability. This is often called a ping sweep, and
410 is more reliable than pinging the broadcast address because many
411 hosts do not reply to broadcast queries.
412 The default host discovery done with -sn consists of an ICMP echo
414 request, TCP SYN to port 443, TCP ACK to port 80, and an ICMP
415 timestamp request by default. When executed by an unprivileged
416 user, only SYN packets are sent (using a connect call) to ports 80
417 and 443 on the target. When a privileged user tries to scan targets
418 on a local ethernet network, ARP requests are used unless --send-ip
419 was specified. The -sn option can be combined with any of the
420 discovery probe types (the -P* options) for greater flexibility. If
421 any of those probe type and port number options are used, the
422 default probes are overridden. When strict firewalls are in place
423 between the source host running Nmap and the target network, using
424 those advanced techniques is recommended. Otherwise hosts could be
425 missed when the firewall drops probes or their responses.
426 In previous releases of Nmap, -sn was known as -sP.
428 -Pn (No ping)
430 This option skips the host discovery stage altogether. Normally,
431 Nmap uses this stage to determine active machines for heavier
432 scanning and to gauge the speed of the network. By default, Nmap
433 only performs heavy probing such as port scans, version detection,
434 or OS detection against hosts that are found to be up. Disabling
435 host discovery with -Pn causes Nmap to attempt the requested
436 scanning functions against every target IP address specified. So if
437 a /16 sized network is specified on the command line, all 65,536 IP
438 addresses are scanned. Proper host discovery is skipped as with the
439 list scan, but instead of stopping and printing the target list,
440 Nmap continues to perform requested functions as if each target IP
441 is active. Default timing parameters are used, which may result in
442 slower scans. To skip host discovery and port scan, while still
443 allowing NSE to run, use the two options -Pn -sn together.
444 For machines on a local ethernet network, ARP scanning will still
446 be performed (unless --disable-arp-ping or --send-ip is specified)
447 because Nmap needs MAC addresses to further scan target hosts. In
448 previous versions of Nmap, -Pn was -P0 and -PN.
449 -PS port list (TCP SYN Ping)
451 This option sends an empty TCP packet with the SYN flag set. The
452 default destination port is 80 (configurable at compile time by
453 changing DEFAULT_TCP_PROBE_PORT_SPEC in nmap.h). Alternate ports
454 can be specified as a parameter. The syntax is the same as for the
455 -p except that port type specifiers like T: are not allowed.
456 Examples are -PS22 and -PS22-25,80,113,1050,35000. Note that there
457 can be no space between -PS and the port list. If multiple probes
458 are specified they will be sent in parallel.
459 The SYN flag suggests to the remote system that you are attempting
461 to establish a connection. Normally the destination port will be
462 closed, and a RST (reset) packet sent back. If the port happens to
463 be open, the target will take the second step of a TCP
464 three-way-handshake by responding with a SYN/ACK TCP packet. The
465 machine running Nmap then tears down the nascent connection by
466 responding with a RST rather than sending an ACK packet which would
467 complete the three-way-handshake and establish a full connection.
468 The RST packet is sent by the kernel of the machine running Nmap in
469 response to the unexpected SYN/ACK, not by Nmap itself.
470 Nmap does not care whether the port is open or closed. Either the
472 RST or SYN/ACK response discussed previously tell Nmap that the
473 host is available and responsive.
474 On Unix boxes, only the privileged user root is generally able to
476 send and receive raw TCP packets. For unprivileged users, a
477 workaround is automatically employed whereby the connect system
478 call is initiated against each target port. This has the effect of
479 sending a SYN packet to the target host, in an attempt to establish
480 a connection. If connect returns with a quick success or an
481 ECONNREFUSED failure, the underlying TCP stack must have received a
482 SYN/ACK or RST and the host is marked available. If the connection
483 attempt is left hanging until a timeout is reached, the host is
484 marked as down.
485 -PA port list (TCP ACK Ping)
487 The TCP ACK ping is quite similar to the just-discussed SYN ping.
488 The difference, as you could likely guess, is that the TCP ACK flag
489 is set instead of the SYN flag. Such an ACK packet purports to be
490 acknowledging data over an established TCP connection, but no such
491 connection exists. So remote hosts should always respond with a RST
492 packet, disclosing their existence in the process.
493 The -PA option uses the same default port as the SYN probe (80) and
495 can also take a list of destination ports in the same format. If an
496 unprivileged user tries this, the connect workaround discussed
497 previously is used. This workaround is imperfect because connect is
498 actually sending a SYN packet rather than an ACK.
499 The reason for offering both SYN and ACK ping probes is to maximize
501 the chances of bypassing firewalls. Many administrators configure
502 routers and other simple firewalls to block incoming SYN packets
503 except for those destined for public services like the company web
504 site or mail server. This prevents other incoming connections to
505 the organization, while allowing users to make unobstructed
506 outgoing connections to the Internet. This non-stateful approach
507 takes up few resources on the firewall/router and is widely
508 supported by hardware and software filters. The Linux
509 Netfilter/iptables firewall software offers the --syn convenience
510 option to implement this stateless approach. When stateless
511 firewall rules such as this are in place, SYN ping probes (-PS) are
512 likely to be blocked when sent to closed target ports. In such
513 cases, the ACK probe shines as it cuts right through these rules.
514 Another common type of firewall uses stateful rules that drop
516 unexpected packets. This feature was initially found mostly on
517 high-end firewalls, though it has become much more common over the
518 years. The Linux Netfilter/iptables system supports this through
519 the --state option, which categorizes packets based on connection
520 state. A SYN probe is more likely to work against such a system, as
521 unexpected ACK packets are generally recognized as bogus and
522 dropped. A solution to this quandary is to send both SYN and ACK
523 probes by specifying -PS and -PA.
524 -PU port list (UDP Ping)
526 Another host discovery option is the UDP ping, which sends a UDP
527 packet to the given ports. For most ports, the packet will be
528 empty, though some use a protocol-specific payload that is more
529 likely to elicit a response. The payload database is described at
530 https://nmap.org/book/nmap-payloads.html.
531 Packet content can also be affected with the --data, --data-string,
533 and --data-length options.
534 The port list takes the same format as with the previously
536 discussed -PS and -PA options. If no ports are specified, the
537 default is 40125. This default can be configured at compile-time
538 by changing DEFAULT_UDP_PROBE_PORT_SPEC in nmap.h. A highly
539 uncommon port is used by default because sending to open ports is
540 often undesirable for this particular scan type.
541 Upon hitting a closed port on the target machine, the UDP probe
543 should elicit an ICMP port unreachable packet in return. This
544 signifies to Nmap that the machine is up and available. Many other
545 types of ICMP errors, such as host/network unreachables or TTL
546 exceeded are indicative of a down or unreachable host. A lack of
547 response is also interpreted this way. If an open port is reached,
548 most services simply ignore the empty packet and fail to return any
549 response. This is why the default probe port is 40125, which is
550 highly unlikely to be in use. A few services, such as the Character
551 Generator (chargen) protocol, will respond to an empty UDP packet,
552 and thus disclose to Nmap that the machine is available.
553 The primary advantage of this scan type is that it bypasses
555 firewalls and filters that only screen TCP. For example, I once
556 owned a Linksys BEFW11S4 wireless broadband router. The external
557 interface of this device filtered all TCP ports by default, but UDP
558 probes would still elicit port unreachable messages and thus give
559 away the device.
560 -PY port list (SCTP INIT Ping)
562 This option sends an SCTP packet containing a minimal INIT chunk.
563 The default destination port is 80 (configurable at compile time by
564 changing DEFAULT_SCTP_PROBE_PORT_SPEC in nmap.h). Alternate ports
565 can be specified as a parameter. The syntax is the same as for the
566 -p except that port type specifiers like S: are not allowed.
567 Examples are -PY22 and -PY22,80,179,5060. Note that there can be no
568 space between -PY and the port list. If multiple probes are
569 specified they will be sent in parallel.
570 The INIT chunk suggests to the remote system that you are
572 attempting to establish an association. Normally the destination
573 port will be closed, and an ABORT chunk will be sent back. If the
574 port happens to be open, the target will take the second step of an
575 SCTP four-way-handshake by responding with an INIT-ACK chunk. If
576 the machine running Nmap has a functional SCTP stack, then it tears
577 down the nascent association by responding with an ABORT chunk
578 rather than sending a COOKIE-ECHO chunk which would be the next
579 step in the four-way-handshake. The ABORT packet is sent by the
580 kernel of the machine running Nmap in response to the unexpected
581 INIT-ACK, not by Nmap itself.
582 Nmap does not care whether the port is open or closed. Either the
584 ABORT or INIT-ACK response discussed previously tell Nmap that the
585 host is available and responsive.
586 On Unix boxes, only the privileged user root is generally able to
588 send and receive raw SCTP packets. Using SCTP INIT Pings is
589 currently not possible for unprivileged users.
590 -PE; -PP; -PM (ICMP Ping Types)
592 In addition to the unusual TCP, UDP and SCTP host discovery types
593 discussed previously, Nmap can send the standard packets sent by
594 the ubiquitous ping program. Nmap sends an ICMP type 8 (echo
595 request) packet to the target IP addresses, expecting a type 0
596 (echo reply) in return from available hosts. Unfortunately for
597 network explorers, many hosts and firewalls now block these
598 packets, rather than responding as required by RFC 1122[2]. For
599 this reason, ICMP-only scans are rarely reliable enough against
600 unknown targets over the Internet. But for system administrators
601 monitoring an internal network, they can be a practical and
602 efficient approach. Use the -PE option to enable this echo request
603 behavior.
604 While echo request is the standard ICMP ping query, Nmap does not
606 stop there. The ICMP standards (RFC 792[3] and RFC 950[4] ) also
607 specify timestamp request, information request, and address mask
608 request packets as codes 13, 15, and 17, respectively. While the
609 ostensible purpose for these queries is to learn information such
610 as address masks and current times, they can easily be used for
611 host discovery. A system that replies is up and available. Nmap
612 does not currently implement information request packets, as they
613 are not widely supported. RFC 1122 insists that “a host SHOULD NOT
614 implement these messages”. Timestamp and address mask queries can
615 be sent with the -PP and -PM options, respectively. A timestamp
616 reply (ICMP code 14) or address mask reply (code 18) discloses that
617 the host is available. These two queries can be valuable when
618 administrators specifically block echo request packets while
619 forgetting that other ICMP queries can be used for the same
620 purpose.
621 -PO protocol list (IP Protocol Ping)
623 One of the newer host discovery options is the IP protocol ping,
624 which sends IP packets with the specified protocol number set in
625 their IP header. The protocol list takes the same format as do port
626 lists in the previously discussed TCP, UDP and SCTP host discovery
627 options. If no protocols are specified, the default is to send
628 multiple IP packets for ICMP (protocol 1), IGMP (protocol 2), and
629 IP-in-IP (protocol 4). The default protocols can be configured at
630 compile-time by changing DEFAULT_PROTO_PROBE_PORT_SPEC in nmap.h.
631 Note that for the ICMP, IGMP, TCP (protocol 6), UDP (protocol 17)
632 and SCTP (protocol 132), the packets are sent with the proper
633 protocol headers while other protocols are sent with no additional
634 data beyond the IP header (unless any of --data, --data-string, or
635 --data-length options are specified).
636 This host discovery method looks for either responses using the
638 same protocol as a probe, or ICMP protocol unreachable messages
639 which signify that the given protocol isn't supported on the
640 destination host. Either type of response signifies that the target
641 host is alive.
642 --disable-arp-ping (No ARP or ND Ping)
644 Nmap normally does ARP or IPv6 Neighbor Discovery (ND) discovery of
645 locally connected ethernet hosts, even if other host discovery
646 options such as -Pn or -PE are used. To disable this implicit
647 behavior, use the --disable-arp-ping option.
648 The default behavior is normally faster, but this option is useful
650 on networks using proxy ARP, in which a router speculatively
651 replies to all ARP requests, making every target appear to be up
652 according to ARP scan.
653 --discovery-ignore-rst
655 In some cases, firewalls may spoof TCP reset (RST) replies in
656 response to probes to unoccupied or disallowed addresses. Since
657 Nmap ordinarily considers RST replies to be proof that the target
658 is up, this can lead to wasted time scanning targets that aren't
659 there. Using the --discovery-ignore-rst will prevent Nmap from
660 considering these replies during host discovery. You may need to
661 select extra host discovery options to ensure you don't miss
662 targets in this case.
663 --traceroute (Trace path to host)
665 Traceroutes are performed post-scan using information from the scan
666 results to determine the port and protocol most likely to reach the
667 target. It works with all scan types except connect scans (-sT) and
668 idle scans (-sI). All traces use Nmap's dynamic timing model and
669 are performed in parallel.
670 Traceroute works by sending packets with a low TTL (time-to-live)
672 in an attempt to elicit ICMP Time Exceeded messages from
673 intermediate hops between the scanner and the target host. Standard
674 traceroute implementations start with a TTL of 1 and increment the
675 TTL until the destination host is reached. Nmap's traceroute starts
676 with a high TTL and then decrements the TTL until it reaches zero.
677 Doing it backwards lets Nmap employ clever caching algorithms to
678 speed up traces over multiple hosts. On average Nmap sends 5–10
679 fewer packets per host, depending on network conditions. If a
680 single subnet is being scanned (i.e. 192.168.0.0/24) Nmap may only
681 have to send two packets to most hosts.
682 -n (No DNS resolution)
684 Tells Nmap to never do reverse DNS resolution on the active IP
686 addresses it finds. Since DNS can be slow even with Nmap's built-in
687 parallel stub resolver, this option can slash scanning times.
688 -R (DNS resolution for all targets)
690 Tells Nmap to always do reverse DNS resolution on the target IP
691 addresses. Normally reverse DNS is only performed against
692 responsive (online) hosts.
693 --resolve-all (Scan each resolved address)
695 If a hostname target resolves to more than one address, scan all of
696 them. The default behavior is to only scan the first resolved
697 address. Regardless, only addresses in the appropriate address
698 family will be scanned: IPv4 by default, IPv6 with -6.
699 --system-dns (Use system DNS resolver)
701 By default, Nmap reverse-resolves IP addresses by sending queries
702 directly to the name servers configured on your host and then
703 listening for responses. Many requests (often dozens) are performed
704 in parallel to improve performance. Specify this option to use your
705 system resolver instead (one IP at a time via the getnameinfo
706 call). This is slower and rarely useful unless you find a bug in
707 the Nmap parallel resolver (please let us know if you do). The
708 system resolver is always used for forward lookups (getting an IP
709 address from a hostname).
710 --dns-servers server1[,server2[,...]] (Servers to use for reverse DNS
712 queries)
713 By default, Nmap determines your DNS servers (for rDNS resolution)
714 from your resolv.conf file (Unix) or the Registry (Win32).
715 Alternatively, you may use this option to specify alternate
716 servers. This option is not honored if you are using --system-dns.
717 Using multiple DNS servers is often faster, especially if you
718 choose authoritative servers for your target IP space. This option
719 can also improve stealth, as your requests can be bounced off just
720 about any recursive DNS server on the Internet.
721 This option also comes in handy when scanning private networks.
723 Sometimes only a few name servers provide proper rDNS information,
724 and you may not even know where they are. You can scan the network
725 for port 53 (perhaps with version detection), then try Nmap list
726 scans (-sL) specifying each name server one at a time with
727 --dns-servers until you find one which works.
728 This option might not be honored if the DNS response exceeds the
730 size of a UDP packet. In such a situation our DNS resolver will
731 make the best effort to extract a response from the truncated
732 packet, and if not successful it will fall back to using the system
733 resolver. Also, responses that contain CNAME aliases will fall back
734 to the system resolver.
735
737 While Nmap has grown in functionality over the years, it began as an
738 efficient port scanner, and that remains its core function. The simple
739 command nmap target scans 1,000 TCP ports on the host target. While
740 many port scanners have traditionally lumped all ports into the open or
741 closed states, Nmap is much more granular. It divides ports into six
742 states: open, closed, filtered, unfiltered, open|filtered, or
743 closed|filtered.
744 These states are not intrinsic properties of the port itself, but
746 describe how Nmap sees them. For example, an Nmap scan from the same
747 network as the target may show port 135/tcp as open, while a scan at
748 the same time with the same options from across the Internet might show
749 that port as filtered.
750 The six port states recognized by Nmap
752 open
754 An application is actively accepting TCP connections, UDP datagrams
755 or SCTP associations on this port. Finding these is often the
756 primary goal of port scanning. Security-minded people know that
757 each open port is an avenue for attack. Attackers and pen-testers
758 want to exploit the open ports, while administrators try to close
759 or protect them with firewalls without thwarting legitimate users.
760 Open ports are also interesting for non-security scans because they
761 show services available for use on the network.
762 closed
764 A closed port is accessible (it receives and responds to Nmap probe
765 packets), but there is no application listening on it. They can be
766 helpful in showing that a host is up on an IP address (host
767 discovery, or ping scanning), and as part of OS detection. Because
768 closed ports are reachable, it may be worth scanning later in case
769 some open up. Administrators may want to consider blocking such
770 ports with a firewall. Then they would appear in the filtered
771 state, discussed next.
772 filtered
774 Nmap cannot determine whether the port is open because packet
775 filtering prevents its probes from reaching the port. The filtering
776 could be from a dedicated firewall device, router rules, or
777 host-based firewall software. These ports frustrate attackers
778 because they provide so little information. Sometimes they respond
779 with ICMP error messages such as type 3 code 13 (destination
780 unreachable: communication administratively prohibited), but
781 filters that simply drop probes without responding are far more
782 common. This forces Nmap to retry several times just in case the
783 probe was dropped due to network congestion rather than filtering.
784 This slows down the scan dramatically.
785 unfiltered
787 The unfiltered state means that a port is accessible, but Nmap is
788 unable to determine whether it is open or closed. Only the ACK
789 scan, which is used to map firewall rulesets, classifies ports into
790 this state. Scanning unfiltered ports with other scan types such as
791 Window scan, SYN scan, or FIN scan, may help resolve whether the
792 port is open.
793 open|filtered
795 Nmap places ports in this state when it is unable to determine
796 whether a port is open or filtered. This occurs for scan types in
797 which open ports give no response. The lack of response could also
798 mean that a packet filter dropped the probe or any response it
799 elicited. So Nmap does not know for sure whether the port is open
800 or being filtered. The UDP, IP protocol, FIN, NULL, and Xmas scans
801 classify ports this way.
802 closed|filtered
804 This state is used when Nmap is unable to determine whether a port
805 is closed or filtered. It is only used for the IP ID idle scan.
806
808 As a novice performing automotive repair, I can struggle for hours
809 trying to fit my rudimentary tools (hammer, duct tape, wrench, etc.) to
810 the task at hand. When I fail miserably and tow my jalopy to a real
811 mechanic, he invariably fishes around in a huge tool chest until
812 pulling out the perfect gizmo which makes the job seem effortless. The
813 art of port scanning is similar. Experts understand the dozens of scan
814 techniques and choose the appropriate one (or combination) for a given
815 task. Inexperienced users and script kiddies, on the other hand, try to
816 solve every problem with the default SYN scan. Since Nmap is free, the
817 only barrier to port scanning mastery is knowledge. That certainly
818 beats the automotive world, where it may take great skill to determine
819 that you need a strut spring compressor, then you still have to pay
820 thousands of dollars for it.
821 Most of the scan types are only available to privileged users. This is
823 because they send and receive raw packets, which requires root access
824 on Unix systems. Using an administrator account on Windows is
825 recommended, though Nmap sometimes works for unprivileged users on that
826 platform when Npcap has already been loaded into the OS. Requiring root
827 privileges was a serious limitation when Nmap was released in 1997, as
828 many users only had access to shared shell accounts. Now, the world is
829 different. Computers are cheaper, far more people have always-on direct
830 Internet access, and desktop Unix systems (including Linux and Mac OS
831 X) are prevalent. A Windows version of Nmap is now available, allowing
832 it to run on even more desktops. For all these reasons, users have less
833 need to run Nmap from limited shared shell accounts. This is fortunate,
834 as the privileged options make Nmap far more powerful and flexible.
835 While Nmap attempts to produce accurate results, keep in mind that all
837 of its insights are based on packets returned by the target machines
838 (or firewalls in front of them). Such hosts may be untrustworthy and
839 send responses intended to confuse or mislead Nmap. Much more common
840 are non-RFC-compliant hosts that do not respond as they should to Nmap
841 probes. FIN, NULL, and Xmas scans are particularly susceptible to this
842 problem. Such issues are specific to certain scan types and so are
843 discussed in the individual scan type entries.
844 This section documents the dozen or so port scan techniques supported
846 by Nmap. Only one method may be used at a time, except that UDP scan
847 (-sU) and any one of the SCTP scan types (-sY, -sZ) may be combined
848 with any one of the TCP scan types. As a memory aid, port scan type
849 options are of the form -sC, where C is a prominent character in the
850 scan name, usually the first. The one exception to this is the
851 deprecated FTP bounce scan (-b). By default, Nmap performs a SYN Scan,
852 though it substitutes a connect scan if the user does not have proper
853 privileges to send raw packets (requires root access on Unix). Of the
854 scans listed in this section, unprivileged users can only execute
855 connect and FTP bounce scans.
856 -sS (TCP SYN scan)
858 SYN scan is the default and most popular scan option for good
859 reasons. It can be performed quickly, scanning thousands of ports
860 per second on a fast network not hampered by restrictive firewalls.
861 It is also relatively unobtrusive and stealthy since it never
862 completes TCP connections. SYN scan works against any compliant TCP
863 stack rather than depending on idiosyncrasies of specific platforms
864 as Nmap's FIN/NULL/Xmas, Maimon and idle scans do. It also allows
865 clear, reliable differentiation between the open, closed, and
866 filtered states.
867 This technique is often referred to as half-open scanning, because
869 you don't open a full TCP connection. You send a SYN packet, as if
870 you are going to open a real connection and then wait for a
871 response. A SYN/ACK indicates the port is listening (open), while a
872 RST (reset) is indicative of a non-listener. If no response is
873 received after several retransmissions, the port is marked as
874 filtered. The port is also marked filtered if an ICMP unreachable
875 error (type 3, code 0, 1, 2, 3, 9, 10, or 13) is received. The port
876 is also considered open if a SYN packet (without the ACK flag) is
877 received in response. This can be due to an extremely rare TCP
878 feature known as a simultaneous open or split handshake connection
879 (see https://nmap.org/misc/split-handshake.pdf).
880 -sT (TCP connect scan)
882 TCP connect scan is the default TCP scan type when SYN scan is not
883 an option. This is the case when a user does not have raw packet
884 privileges. Instead of writing raw packets as most other scan types
885 do, Nmap asks the underlying operating system to establish a
886 connection with the target machine and port by issuing the connect
887 system call. This is the same high-level system call that web
888 browsers, P2P clients, and most other network-enabled applications
889 use to establish a connection. It is part of a programming
890 interface known as the Berkeley Sockets API. Rather than read raw
891 packet responses off the wire, Nmap uses this API to obtain status
892 information on each connection attempt.
893 When SYN scan is available, it is usually a better choice. Nmap has
895 less control over the high level connect call than with raw
896 packets, making it less efficient. The system call completes
897 connections to open target ports rather than performing the
898 half-open reset that SYN scan does. Not only does this take longer
899 and require more packets to obtain the same information, but target
900 machines are more likely to log the connection. A decent IDS will
901 catch either, but most machines have no such alarm system. Many
902 services on your average Unix system will add a note to syslog, and
903 sometimes a cryptic error message, when Nmap connects and then
904 closes the connection without sending data. Truly pathetic services
905 crash when this happens, though that is uncommon. An administrator
906 who sees a bunch of connection attempts in her logs from a single
907 system should know that she has been connect scanned.
908 -sU (UDP scans)
910 While most popular services on the Internet run over the TCP
911 protocol, UDP[5] services are widely deployed. DNS, SNMP, and DHCP
912 (registered ports 53, 161/162, and 67/68) are three of the most
913 common. Because UDP scanning is generally slower and more difficult
914 than TCP, some security auditors ignore these ports. This is a
915 mistake, as exploitable UDP services are quite common and attackers
916 certainly don't ignore the whole protocol. Fortunately, Nmap can
917 help inventory UDP ports.
918 UDP scan is activated with the -sU option. It can be combined with
920 a TCP scan type such as SYN scan (-sS) to check both protocols
921 during the same run.
922 UDP scan works by sending a UDP packet to every targeted port. For
924 some common ports such as 53 and 161, a protocol-specific payload
925 is sent to increase response rate, but for most ports the packet is
926 empty unless the --data, --data-string, or --data-length options
927 are specified. If an ICMP port unreachable error (type 3, code 3)
928 is returned, the port is closed. Other ICMP unreachable errors
929 (type 3, codes 0, 1, 2, 9, 10, or 13) mark the port as filtered.
930 Occasionally, a service will respond with a UDP packet, proving
931 that it is open. If no response is received after retransmissions,
932 the port is classified as open|filtered. This means that the port
933 could be open, or perhaps packet filters are blocking the
934 communication. Version detection (-sV) can be used to help
935 differentiate the truly open ports from the filtered ones.
936 A big challenge with UDP scanning is doing it quickly. Open and
938 filtered ports rarely send any response, leaving Nmap to time out
939 and then conduct retransmissions just in case the probe or response
940 were lost. Closed ports are often an even bigger problem. They
941 usually send back an ICMP port unreachable error. But unlike the
942 RST packets sent by closed TCP ports in response to a SYN or
943 connect scan, many hosts rate limit ICMP port unreachable messages
944 by default. Linux and Solaris are particularly strict about this.
945 For example, the Linux 2.4.20 kernel limits destination unreachable
946 messages to one per second (in net/ipv4/icmp.c).
947 Nmap detects rate limiting and slows down accordingly to avoid
949 flooding the network with useless packets that the target machine
950 will drop. Unfortunately, a Linux-style limit of one packet per
951 second makes a 65,536-port scan take more than 18 hours. Ideas for
952 speeding your UDP scans up include scanning more hosts in parallel,
953 doing a quick scan of just the popular ports first, scanning from
954 behind the firewall, and using --host-timeout to skip slow hosts.
955 -sY (SCTP INIT scan)
957 SCTP[6] is a relatively new alternative to the TCP and UDP
958 protocols, combining most characteristics of TCP and UDP, and also
959 adding new features like multi-homing and multi-streaming. It is
960 mostly being used for SS7/SIGTRAN related services but has the
961 potential to be used for other applications as well. SCTP INIT scan
962 is the SCTP equivalent of a TCP SYN scan. It can be performed
963 quickly, scanning thousands of ports per second on a fast network
964 not hampered by restrictive firewalls. Like SYN scan, INIT scan is
965 relatively unobtrusive and stealthy, since it never completes SCTP
966 associations. It also allows clear, reliable differentiation
967 between the open, closed, and filtered states.
968 This technique is often referred to as half-open scanning, because
970 you don't open a full SCTP association. You send an INIT chunk, as
971 if you are going to open a real association and then wait for a
972 response. An INIT-ACK chunk indicates the port is listening (open),
973 while an ABORT chunk is indicative of a non-listener. If no
974 response is received after several retransmissions, the port is
975 marked as filtered. The port is also marked filtered if an ICMP
976 unreachable error (type 3, code 0, 1, 2, 3, 9, 10, or 13) is
977 received.
978 -sN; -sF; -sX (TCP NULL, FIN, and Xmas scans)
980 These three scan types (even more are possible with the --scanflags
981 option described in the next section) exploit a subtle loophole in
982 the TCP RFC[7] to differentiate between open and closed ports. Page
983 65 of RFC 793 says that “if the [destination] port state is CLOSED
984 .... an incoming segment not containing a RST causes a RST to be
985 sent in response.” Then the next page discusses packets sent to
986 open ports without the SYN, RST, or ACK bits set, stating that:
987 “you are unlikely to get here, but if you do, drop the segment, and
988 return.”
989 When scanning systems compliant with this RFC text, any packet not
991 containing SYN, RST, or ACK bits will result in a returned RST if
992 the port is closed and no response at all if the port is open. As
993 long as none of those three bits are included, any combination of
994 the other three (FIN, PSH, and URG) are OK. Nmap exploits this with
995 three scan types:
996 Null scan (-sN)
998 Does not set any bits (TCP flag header is 0)
999 FIN scan (-sF)
1001 Sets just the TCP FIN bit.
1002 Xmas scan (-sX)
1004 Sets the FIN, PSH, and URG flags, lighting the packet up like a
1005 Christmas tree.
1006 These three scan types are exactly the same in behavior except for
1008 the TCP flags set in probe packets. If a RST packet is received,
1009 the port is considered closed, while no response means it is
1010 open|filtered. The port is marked filtered if an ICMP unreachable
1011 error (type 3, code 0, 1, 2, 3, 9, 10, or 13) is received.
1012 The key advantage to these scan types is that they can sneak
1014 through certain non-stateful firewalls and packet filtering
1015 routers. Another advantage is that these scan types are a little
1016 more stealthy than even a SYN scan. Don't count on this though—most
1017 modern IDS products can be configured to detect them. The big
1018 downside is that not all systems follow RFC 793 to the letter. A
1019 number of systems send RST responses to the probes regardless of
1020 whether the port is open or not. This causes all of the ports to be
1021 labeled closed. Major operating systems that do this are Microsoft
1022 Windows, many Cisco devices, BSDI, and IBM OS/400. This scan does
1023 work against most Unix-based systems though. Another downside of
1024 these scans is that they can't distinguish open ports from certain
1025 filtered ones, leaving you with the response open|filtered.
1026 -sA (TCP ACK scan)
1028 This scan is different than the others discussed so far in that it
1029 never determines open (or even open|filtered) ports. It is used to
1030 map out firewall rulesets, determining whether they are stateful or
1031 not and which ports are filtered.
1032 The ACK scan probe packet has only the ACK flag set (unless you use
1034 --scanflags). When scanning unfiltered systems, open and closed
1035 ports will both return a RST packet. Nmap then labels them as
1036 unfiltered, meaning that they are reachable by the ACK packet, but
1037 whether they are open or closed is undetermined. Ports that don't
1038 respond, or send certain ICMP error messages back (type 3, code 0,
1039 1, 2, 3, 9, 10, or 13), are labeled filtered.
1040 -sW (TCP Window scan)
1042 Window scan is exactly the same as ACK scan except that it exploits
1043 an implementation detail of certain systems to differentiate open
1044 ports from closed ones, rather than always printing unfiltered when
1045 a RST is returned. It does this by examining the TCP Window field
1046 of the RST packets returned. On some systems, open ports use a
1047 positive window size (even for RST packets) while closed ones have
1048 a zero window. So instead of always listing a port as unfiltered
1049 when it receives a RST back, Window scan lists the port as open or
1050 closed if the TCP Window value in that reset is positive or zero,
1051 respectively.
1052 This scan relies on an implementation detail of a minority of
1054 systems out on the Internet, so you can't always trust it. Systems
1055 that don't support it will usually return all ports closed. Of
1056 course, it is possible that the machine really has no open ports.
1057 If most scanned ports are closed but a few common port numbers
1058 (such as 22, 25, 53) are filtered, the system is most likely
1059 susceptible. Occasionally, systems will even show the exact
1060 opposite behavior. If your scan shows 1,000 open ports and three
1061 closed or filtered ports, then those three may very well be the
1062 truly open ones.
1063 -sM (TCP Maimon scan)
1065 The Maimon scan is named after its discoverer, Uriel Maimon. He
1066 described the technique in Phrack Magazine issue #49 (November
1067 1996). Nmap, which included this technique, was released two
1068 issues later. This technique is exactly the same as NULL, FIN, and
1069 Xmas scans, except that the probe is FIN/ACK. According to RFC
1070 793[7] (TCP), a RST packet should be generated in response to such
1071 a probe whether the port is open or closed. However, Uriel noticed
1072 that many BSD-derived systems simply drop the packet if the port is
1073 open.
1074 --scanflags (Custom TCP scan)
1076 Truly advanced Nmap users need not limit themselves to the canned
1077 scan types offered. The --scanflags option allows you to design
1078 your own scan by specifying arbitrary TCP flags. Let your creative
1079 juices flow, while evading intrusion detection systems whose
1080 vendors simply paged through the Nmap man page adding specific
1081 rules!
1082 The --scanflags argument can be a numerical flag value such as 9
1084 (PSH and FIN), but using symbolic names is easier. Just mash
1085 together any combination of URG, ACK, PSH, RST, SYN, and FIN. For
1086 example, --scanflags URGACKPSHRSTSYNFIN sets everything, though
1087 it's not very useful for scanning. The order these are specified in
1088 is irrelevant.
1089 In addition to specifying the desired flags, you can specify a TCP
1091 scan type (such as -sA or -sF). That base type tells Nmap how to
1092 interpret responses. For example, a SYN scan considers no-response
1093 to indicate a filtered port, while a FIN scan treats the same as
1094 open|filtered. Nmap will behave the same way it does for the base
1095 scan type, except that it will use the TCP flags you specify
1096 instead. If you don't specify a base type, SYN scan is used.
1097 -sZ (SCTP COOKIE ECHO scan)
1099 SCTP COOKIE ECHO scan is a more advanced SCTP scan. It takes
1100 advantage of the fact that SCTP implementations should silently
1101 drop packets containing COOKIE ECHO chunks on open ports, but send
1102 an ABORT if the port is closed. The advantage of this scan type is
1103 that it is not as obvious a port scan than an INIT scan. Also,
1104 there may be non-stateful firewall rulesets blocking INIT chunks,
1105 but not COOKIE ECHO chunks. Don't be fooled into thinking that this
1106 will make a port scan invisible; a good IDS will be able to detect
1107 SCTP COOKIE ECHO scans too. The downside is that SCTP COOKIE ECHO
1108 scans cannot differentiate between open and filtered ports, leaving
1109 you with the state open|filtered in both cases.
1110 -sI zombie host[:probeport] (idle scan)
1112 This advanced scan method allows for a truly blind TCP port scan of
1113 the target (meaning no packets are sent to the target from your
1114 real IP address). Instead, a unique side-channel attack exploits
1115 predictable IP fragmentation ID sequence generation on the zombie
1116 host to glean information about the open ports on the target. IDS
1117 systems will display the scan as coming from the zombie machine you
1118 specify (which must be up and meet certain criteria). This
1119 fascinating scan type is too complex to fully describe in this
1120 reference guide, so I wrote and posted an informal paper with full
1121 details at https://nmap.org/book/idlescan.html.
1122 Besides being extraordinarily stealthy (due to its blind nature),
1124 this scan type permits mapping out IP-based trust relationships
1125 between machines. The port listing shows open ports from the
1126 perspective of the zombie host. So you can try scanning a target
1127 using various zombies that you think might be trusted (via
1128 router/packet filter rules).
1129 You can add a colon followed by a port number to the zombie host if
1131 you wish to probe a particular port on the zombie for IP ID
1132 changes. Otherwise Nmap will use the port it uses by default for
1133 TCP pings (80).
1134 -sO (IP protocol scan)
1136 IP protocol scan allows you to determine which IP protocols (TCP,
1137 ICMP, IGMP, etc.) are supported by target machines. This isn't
1138 technically a port scan, since it cycles through IP protocol
1139 numbers rather than TCP or UDP port numbers. Yet it still uses the
1140 -p option to select scanned protocol numbers, reports its results
1141 within the normal port table format, and even uses the same
1142 underlying scan engine as the true port scanning methods. So it is
1143 close enough to a port scan that it belongs here.
1144 Besides being useful in its own right, protocol scan demonstrates
1146 the power of open-source software. While the fundamental idea is
1147 pretty simple, I had not thought to add it nor received any
1148 requests for such functionality. Then in the summer of 2000,
1149 Gerhard Rieger conceived the idea, wrote an excellent patch
1150 implementing it, and sent it to the announce mailing list (then
1151 called nmap-hackers). I incorporated that patch into the Nmap tree
1152 and released a new version the next day. Few pieces of commercial
1153 software have users enthusiastic enough to design and contribute
1154 their own improvements!
1155 Protocol scan works in a similar fashion to UDP scan. Instead of
1157 iterating through the port number field of a UDP packet, it sends
1158 IP packet headers and iterates through the eight-bit IP protocol
1159 field. The headers are usually empty, containing no data and not
1160 even the proper header for the claimed protocol. The exceptions are
1161 TCP, UDP, ICMP, SCTP, and IGMP. A proper protocol header for those
1162 is included since some systems won't send them otherwise and
1163 because Nmap already has functions to create them. Instead of
1164 watching for ICMP port unreachable messages, protocol scan is on
1165 the lookout for ICMP protocol unreachable messages. If Nmap
1166 receives any response in any protocol from the target host, Nmap
1167 marks that protocol as open. An ICMP protocol unreachable error
1168 (type 3, code 2) causes the protocol to be marked as closed while
1169 port unreachable (type 3, code 3) marks the protocol open. Other
1170 ICMP unreachable errors (type 3, code 0, 1, 9, 10, or 13) cause the
1171 protocol to be marked filtered (though they prove that ICMP is open
1172 at the same time). If no response is received after
1173 retransmissions, the protocol is marked open|filtered
1174 -b FTP relay host (FTP bounce scan)
1176 An interesting feature of the FTP protocol (RFC 959[8]) is support
1177 for so-called proxy FTP connections. This allows a user to connect
1178 to one FTP server, then ask that files be sent to a third-party
1179 server. Such a feature is ripe for abuse on many levels, so most
1180 servers have ceased supporting it. One of the abuses this feature
1181 allows is causing the FTP server to port scan other hosts. Simply
1182 ask the FTP server to send a file to each interesting port of a
1183 target host in turn. The error message will describe whether the
1184 port is open or not. This is a good way to bypass firewalls because
1185 organizational FTP servers are often placed where they have more
1186 access to other internal hosts than any old Internet host would.
1187 Nmap supports FTP bounce scan with the -b option. It takes an
1188 argument of the form username:password@server:port. Server is the
1189 name or IP address of a vulnerable FTP server. As with a normal
1190 URL, you may omit username:password, in which case anonymous login
1191 credentials (user: anonymous password:-wwwuser@) are used. The port
1192 number (and preceding colon) may be omitted as well, in which case
1193 the default FTP port (21) on server is used.
1194 This vulnerability was widespread in 1997 when Nmap was released,
1196 but has largely been fixed. Vulnerable servers are still around, so
1197 it is worth trying when all else fails. If bypassing a firewall is
1198 your goal, scan the target network for port 21 (or even for any FTP
1199 services if you scan all ports with version detection) and use the
1200 ftp-bounce NSE script. Nmap will tell you whether the host is
1201 vulnerable or not. If you are just trying to cover your tracks, you
1202 don't need to (and, in fact, shouldn't) limit yourself to hosts on
1203 the target network. Before you go scanning random Internet
1204 addresses for vulnerable FTP servers, consider that sysadmins may
1205 not appreciate you abusing their servers in this way.
1206
1208 In addition to all of the scan methods discussed previously, Nmap
1209 offers options for specifying which ports are scanned and whether the
1210 scan order is randomized or sequential. By default, Nmap scans the most
1211 common 1,000 ports for each protocol.
1212 -p port ranges (Only scan specified ports)
1215 This option specifies which ports you want to scan and overrides
1216 the default. Individual port numbers are OK, as are ranges
1217 separated by a hyphen (e.g. 1-1023). The beginning and/or end
1218 values of a range may be omitted, causing Nmap to use 1 and 65535,
1219 respectively. So you can specify -p- to scan ports from 1 through
1220 65535. Scanning port zero is allowed if you specify it explicitly.
1221 For IP protocol scanning (-sO), this option specifies the protocol
1222 numbers you wish to scan for (0–255).
1223 When scanning a combination of protocols (e.g. TCP and UDP), you
1225 can specify a particular protocol by preceding the port numbers by
1226 T: for TCP, U: for UDP, S: for SCTP, or P: for IP Protocol. The
1227 qualifier lasts until you specify another qualifier. For example,
1228 the argument -p U:53,111,137,T:21-25,80,139,8080 would scan UDP
1229 ports 53, 111,and 137, as well as the listed TCP ports. Note that
1230 to scan both UDP and TCP, you have to specify -sU and at least one
1231 TCP scan type (such as -sS, -sF, or -sT). If no protocol qualifier
1232 is given, the port numbers are added to all protocol lists. Ports
1233 can also be specified by name according to what the port is
1234 referred to in the nmap-services. You can even use the wildcards *
1235 and ? with the names. For example, to scan FTP and all ports whose
1236 names begin with “http”, use -p ftp,http*. Be careful about shell
1237 expansions and quote the argument to -p if unsure.
1238 Ranges of ports can be surrounded by square brackets to indicate
1240 ports inside that range that appear in nmap-services. For example,
1241 the following will scan all ports in nmap-services equal to or
1242 below 1024: -p [-1024]. Be careful with shell expansions and quote
1243 the argument to -p if unsure.
1244 --exclude-ports port ranges (Exclude the specified ports from scanning)
1246 This option specifies which ports you do want Nmap to exclude from
1247 scanning. The port ranges are specified similar to -p. For IP
1248 protocol scanning (-sO), this option specifies the protocol numbers
1249 you wish to exclude (0–255).
1250 When ports are asked to be excluded, they are excluded from all
1252 types of scans (i.e. they will not be scanned under any
1253 circumstances). This also includes the discovery phase.
1254 -F (Fast (limited port) scan)
1256 Specifies that you wish to scan fewer ports than the default.
1257 Normally Nmap scans the most common 1,000 ports for each scanned
1258 protocol. With -F, this is reduced to 100.
1259 Nmap needs an nmap-services file with frequency information in
1261 order to know which ports are the most common. If port frequency
1262 information isn't available, perhaps because of the use of a custom
1263 nmap-services file, Nmap scans all named ports plus ports 1-1024.
1264 In that case, -F means to scan only ports that are named in the
1265 services file.
1266 -r (Don't randomize ports)
1268 By default, Nmap randomizes the scanned port order (except that
1269 certain commonly accessible ports are moved near the beginning for
1270 efficiency reasons). This randomization is normally desirable, but
1271 you can specify -r for sequential (sorted from lowest to highest)
1272 port scanning instead.
1273 --port-ratio ratio<decimal number between 0 and 1>
1275 Scans all ports in nmap-services file with a ratio greater than the
1276 one given. ratio must be between 0.0 and 1.0.
1277 --top-ports n
1279 Scans the n highest-ratio ports found in nmap-services file after
1280 excluding all ports specified by --exclude-ports. n must be 1 or
1281 greater.
1282
1284 Point Nmap at a remote machine and it might tell you that ports 25/tcp,
1285 80/tcp, and 53/udp are open. Using its nmap-services database of about
1286 2,200 well-known services, Nmap would report that those ports probably
1287 correspond to a mail server (SMTP), web server (HTTP), and name server
1288 (DNS) respectively. This lookup is usually accurate—the vast majority
1289 of daemons listening on TCP port 25 are, in fact, mail servers.
1290 However, you should not bet your security on this! People can and do
1291 run services on strange ports.
1292 Even if Nmap is right, and the hypothetical server above is running
1294 SMTP, HTTP, and DNS servers, that is not a lot of information. When
1295 doing vulnerability assessments (or even simple network inventories) of
1296 your companies or clients, you really want to know which mail and DNS
1297 servers and versions are running. Having an accurate version number
1298 helps dramatically in determining which exploits a server is vulnerable
1299 to. Version detection helps you obtain this information.
1300 After TCP and/or UDP ports are discovered using one of the other scan
1302 methods, version detection interrogates those ports to determine more
1303 about what is actually running. The nmap-service-probes database
1304 contains probes for querying various services and match expressions to
1305 recognize and parse responses. Nmap tries to determine the service
1306 protocol (e.g. FTP, SSH, Telnet, HTTP), the application name (e.g. ISC
1307 BIND, Apache httpd, Solaris telnetd), the version number, hostname,
1308 device type (e.g. printer, router), the OS family (e.g. Windows,
1309 Linux). When possible, Nmap also gets the Common Platform Enumeration
1310 (CPE) representation of this information. Sometimes miscellaneous
1311 details like whether an X server is open to connections, the SSH
1312 protocol version, or the KaZaA user name, are available. Of course,
1313 most services don't provide all of this information. If Nmap was
1314 compiled with OpenSSL support, it will connect to SSL servers to deduce
1315 the service listening behind that encryption layer. Some UDP ports are
1316 left in the open|filtered state after a UDP port scan is unable to
1317 determine whether the port is open or filtered. Version detection will
1318 try to elicit a response from these ports (just as it does with open
1319 ports), and change the state to open if it succeeds. open|filtered TCP
1320 ports are treated the same way. Note that the Nmap -A option enables
1321 version detection among other things. A paper documenting the
1322 workings, usage, and customization of version detection is available at
1323 https://nmap.org/book/vscan.html.
1324 When RPC services are discovered, the Nmap RPC grinder is automatically
1326 used to determine the RPC program and version numbers. It takes all the
1327 TCP/UDP ports detected as RPC and floods them with SunRPC program NULL
1328 commands in an attempt to determine whether they are RPC ports, and if
1329 so, what program and version number they serve up. Thus you can
1330 effectively obtain the same info as rpcinfo -p even if the target's
1331 portmapper is behind a firewall (or protected by TCP wrappers). Decoys
1332 do not currently work with RPC scan.
1333 When Nmap receives responses from a service but cannot match them to
1335 its database, it prints out a special fingerprint and a URL for you to
1336 submit it to if you know for sure what is running on the port. Please
1337 take a couple minutes to make the submission so that your find can
1338 benefit everyone. Thanks to these submissions, Nmap has about 6,500
1339 pattern matches for more than 650 protocols such as SMTP, FTP, HTTP,
1340 etc.
1341 Version detection is enabled and controlled with the following options:
1343 -sV (Version detection)
1345 Enables version detection, as discussed above. Alternatively, you
1346 can use -A, which enables version detection among other things.
1347 -sR is an alias for -sV. Prior to March 2011, it was used to active
1349 the RPC grinder separately from version detection, but now these
1350 options are always combined.
1351 --allports (Don't exclude any ports from version detection)
1353 By default, Nmap version detection skips TCP port 9100 because some
1354 printers simply print anything sent to that port, leading to dozens
1355 of pages of HTTP GET requests, binary SSL session requests, etc.
1356 This behavior can be changed by modifying or removing the Exclude
1357 directive in nmap-service-probes, or you can specify --allports to
1358 scan all ports regardless of any Exclude directive.
1359 --version-intensity intensity (Set version scan intensity)
1361 When performing a version scan (-sV), Nmap sends a series of
1362 probes, each of which is assigned a rarity value between one and
1363 nine. The lower-numbered probes are effective against a wide
1364 variety of common services, while the higher-numbered ones are
1365 rarely useful. The intensity level specifies which probes should be
1366 applied. The higher the number, the more likely it is the service
1367 will be correctly identified. However, high intensity scans take
1368 longer. The intensity must be between 0 and 9. The default is 7.
1369 When a probe is registered to the target port via the
1370 nmap-service-probes ports directive, that probe is tried regardless
1371 of intensity level. This ensures that the DNS probes will always be
1372 attempted against any open port 53, the SSL probe will be done
1373 against 443, etc.
1374 --version-light (Enable light mode)
1376 This is a convenience alias for --version-intensity 2. This light
1377 mode makes version scanning much faster, but it is slightly less
1378 likely to identify services.
1379 --version-all (Try every single probe)
1381 An alias for --version-intensity 9, ensuring that every single
1382 probe is attempted against each port.
1383 --version-trace (Trace version scan activity)
1385 This causes Nmap to print out extensive debugging info about what
1386 version scanning is doing. It is a subset of what you get with
1387 --packet-trace.
1388
1390 One of Nmap's best-known features is remote OS detection using TCP/IP
1391 stack fingerprinting. Nmap sends a series of TCP and UDP packets to the
1392 remote host and examines practically every bit in the responses. After
1393 performing dozens of tests such as TCP ISN sampling, TCP options
1394 support and ordering, IP ID sampling, and the initial window size
1395 check, Nmap compares the results to its nmap-os-db database of more
1396 than 2,600 known OS fingerprints and prints out the OS details if there
1397 is a match. Each fingerprint includes a freeform textual description of
1398 the OS, and a classification which provides the vendor name (e.g. Sun),
1399 underlying OS (e.g. Solaris), OS generation (e.g. 10), and device type
1400 (general purpose, router, switch, game console, etc). Most fingerprints
1401 also have a Common Platform Enumeration (CPE) representation, like
1402 cpe:/o:linux:linux_kernel:2.6.
1403 If Nmap is unable to guess the OS of a machine, and conditions are good
1405 (e.g. at least one open port and one closed port were found), Nmap will
1406 provide a URL you can use to submit the fingerprint if you know (for
1407 sure) the OS running on the machine. By doing this you contribute to
1408 the pool of operating systems known to Nmap and thus it will be more
1409 accurate for everyone.
1410 OS detection enables some other tests which make use of information
1412 that is gathered during the process anyway. One of these is TCP
1413 Sequence Predictability Classification. This measures approximately how
1414 hard it is to establish a forged TCP connection against the remote
1415 host. It is useful for exploiting source-IP based trust relationships
1416 (rlogin, firewall filters, etc) or for hiding the source of an attack.
1417 This sort of spoofing is rarely performed any more, but many machines
1418 are still vulnerable to it. The actual difficulty number is based on
1419 statistical sampling and may fluctuate. It is generally better to use
1420 the English classification such as “worthy challenge” or “trivial
1421 joke”. This is only reported in normal output in verbose (-v) mode.
1422 When verbose mode is enabled along with -O, IP ID sequence generation
1423 is also reported. Most machines are in the “incremental” class, which
1424 means that they increment the ID field in the IP header for each packet
1425 they send. This makes them vulnerable to several advanced information
1426 gathering and spoofing attacks.
1427 Another bit of extra information enabled by OS detection is a guess at
1429 a target's uptime. This uses the TCP timestamp option (RFC 1323[9]) to
1430 guess when a machine was last rebooted. The guess can be inaccurate due
1431 to the timestamp counter not being initialized to zero or the counter
1432 overflowing and wrapping around, so it is printed only in verbose mode.
1433 A paper documenting the workings, usage, and customization of OS
1435 detection is available at https://nmap.org/book/osdetect.html.
1436 OS detection is enabled and controlled with the following options:
1438 -O (Enable OS detection)
1440 Enables OS detection, as discussed above. Alternatively, you can
1441 use -A to enable OS detection along with other things.
1442 --osscan-limit (Limit OS detection to promising targets)
1444 OS detection is far more effective if at least one open and one
1445 closed TCP port are found. Set this option and Nmap will not even
1446 try OS detection against hosts that do not meet this criteria. This
1447 can save substantial time, particularly on -Pn scans against many
1448 hosts. It only matters when OS detection is requested with -O or
1449 -A.
1450 --osscan-guess; --fuzzy (Guess OS detection results)
1452 When Nmap is unable to detect a perfect OS match, it sometimes
1453 offers up near-matches as possibilities. The match has to be very
1454 close for Nmap to do this by default. Either of these (equivalent)
1455 options make Nmap guess more aggressively. Nmap will still tell you
1456 when an imperfect match is printed and display its confidence level
1457 (percentage) for each guess.
1458 --max-os-tries (Set the maximum number of OS detection tries against a
1460 target)
1461 When Nmap performs OS detection against a target and fails to find
1462 a perfect match, it usually repeats the attempt. By default, Nmap
1463 tries five times if conditions are favorable for OS fingerprint
1464 submission, and twice when conditions aren't so good. Specifying a
1465 lower --max-os-tries value (such as 1) speeds Nmap up, though you
1466 miss out on retries which could potentially identify the OS.
1467 Alternatively, a high value may be set to allow even more retries
1468 when conditions are favorable. This is rarely done, except to
1469 generate better fingerprints for submission and integration into
1470 the Nmap OS database.
1471
1473 The Nmap Scripting Engine (NSE) is one of Nmap's most powerful and
1474 flexible features. It allows users to write (and share) simple scripts
1475 (using the Lua programming language[10]
1476 ) to automate a wide variety of networking tasks. Those scripts are
1478 executed in parallel with the speed and efficiency you expect from
1479 Nmap. Users can rely on the growing and diverse set of scripts
1480 distributed with Nmap, or write their own to meet custom needs.
1481 Tasks we had in mind when creating the system include network
1483 discovery, more sophisticated version detection, vulnerability
1484 detection. NSE can even be used for vulnerability exploitation.
1485 To reflect those different uses and to simplify the choice of which
1487 scripts to run, each script contains a field associating it with one or
1488 more categories. Currently defined categories are auth, broadcast,
1489 default. discovery, dos, exploit, external, fuzzer, intrusive,
1490 malware, safe, version, and vuln. These are all described at
1491 https://nmap.org/book/nse-usage.html#nse-categories.
1492 Scripts are not run in a sandbox and thus could accidentally or
1494 maliciously damage your system or invade your privacy. Never run
1495 scripts from third parties unless you trust the authors or have
1496 carefully audited the scripts yourself.
1497 The Nmap Scripting Engine is described in detail at
1499 https://nmap.org/book/nse.html
1500 and is controlled by the following options:
1502 -sC
1504 Performs a script scan using the default set of scripts. It is
1505 equivalent to --script=default. Some of the scripts in this
1506 category are considered intrusive and should not be run against a
1507 target network without permission.
1508 --script filename|category|directory/|expression[,...]
1510 Runs a script scan using the comma-separated list of filenames,
1511 script categories, and directories. Each element in the list may
1512 also be a Boolean expression describing a more complex set of
1513 scripts. Each element is interpreted first as an expression, then
1514 as a category, and finally as a file or directory name.
1515 There are two special features for advanced users only. One is to
1517 prefix script names and expressions with + to force them to run
1518 even if they normally wouldn't (e.g. the relevant service wasn't
1519 detected on the target port). The other is that the argument all
1520 may be used to specify every script in Nmap's database. Be cautious
1521 with this because NSE contains dangerous scripts such as exploits,
1522 brute force authentication crackers, and denial of service attacks.
1523 File and directory names may be relative or absolute. Absolute
1525 names are used directly. Relative paths are looked for in the
1526 scripts of each of the following places until found:
1527 --datadir
1528 $NMAPDIR
1529 ~/.nmap (not searched on Windows)
1530 APPDATA\nmap (only on Windows)
1531 the directory containing the nmap executable
1532 the directory containing the nmap executable, followed by
1533 ../share/nmap (not searched on Windows)
1534 NMAPDATADIR (not searched on Windows)
1535 the current directory.
1536 When a directory name ending in / is given, Nmap loads every file
1538 in the directory whose name ends with .nse. All other files are
1539 ignored and directories are not searched recursively. When a
1540 filename is given, it does not have to have the .nse extension; it
1541 will be added automatically if necessary. Nmap scripts are stored
1542 in a scripts subdirectory of the Nmap data directory by default
1543 (see https://nmap.org/book/data-files.html).
1544 For efficiency, scripts are indexed in a database stored in
1546 scripts/script.db, which lists the category or categories in which
1547 each script belongs. When referring to scripts from script.db by
1548 name, you can use a shell-style ‘*’ wildcard.
1549 nmap --script "http-*"
1551 Loads all scripts whose name starts with http-, such as
1552 http-auth and http-open-proxy. The argument to --script had to
1553 be in quotes to protect the wildcard from the shell.
1554 More complicated script selection can be done using the and, or,
1556 and not operators to build Boolean expressions. The operators have
1557 the same precedence[11] as in Lua: not is the highest, followed by
1558 and and then or. You can alter precedence by using parentheses.
1559 Because expressions contain space characters it is necessary to
1560 quote them.
1561 nmap --script "not intrusive"
1563 Loads every script except for those in the intrusive category.
1564 nmap --script "default or safe"
1566 This is functionally equivalent to nmap --script
1567 "default,safe". It loads all scripts that are in the default
1568 category or the safe category or both.
1569 nmap --script "default and safe"
1571 Loads those scripts that are in both the default and safe
1572 categories.
1573 nmap --script "(default or safe or intrusive) and not http-*"
1575 Loads scripts in the default, safe, or intrusive categories,
1576 except for those whose names start with http-.
1577 --script-args n1=v1,n2={n3=v3},n4={v4,v5}
1579 Lets you provide arguments to NSE scripts. Arguments are a
1580 comma-separated list of name=value pairs. Names and values may be
1581 strings not containing whitespace or the characters ‘{’, ‘}’, ‘=’,
1582 or ‘,’. To include one of these characters in a string, enclose the
1583 string in single or double quotes. Within a quoted string, ‘\’
1584 escapes a quote. A backslash is only used to escape quotation marks
1585 in this special case; in all other cases a backslash is interpreted
1586 literally. Values may also be tables enclosed in {}, just as in
1587 Lua. A table may contain simple string values or more name-value
1588 pairs, including nested tables. Many scripts qualify their
1589 arguments with the script name, as in xmpp-info.server_name. You
1590 may use that full qualified version to affect just the specified
1591 script, or you may pass the unqualified version (server_name in
1592 this case) to affect all scripts using that argument name. A script
1593 will first check for its fully qualified argument name (the name
1594 specified in its documentation) before it accepts an unqualified
1595 argument name. A complex example of script arguments is
1596 --script-args
1597 'user=foo,pass=",{}=bar",whois={whodb=nofollow+ripe},xmpp-info.server_name=localhost'.
1598 The online NSE Documentation Portal at https://nmap.org/nsedoc/
1599 lists the arguments that each script accepts.
1600 --script-args-file filename
1602 Lets you load arguments to NSE scripts from a file. Any arguments
1603 on the command line supersede ones in the file. The file can be an
1604 absolute path, or a path relative to Nmap's usual search path
1605 (NMAPDIR, etc.) Arguments can be comma-separated or
1606 newline-separated, but otherwise follow the same rules as for
1607 --script-args, without requiring special quoting and escaping,
1608 since they are not parsed by the shell.
1609 --script-help filename|category|directory|expression|all[,...]
1611 Shows help about scripts. For each script matching the given
1612 specification, Nmap prints the script name, its categories, and its
1613 description. The specifications are the same as those accepted by
1614 --script; so for example if you want help about the ftp-anon
1615 script, you would run nmap --script-help ftp-anon. In addition to
1616 getting help for individual scripts, you can use this as a preview
1617 of what scripts will be run for a specification, for example with
1618 nmap --script-help default.
1619 --script-trace
1621 This option does what --packet-trace does, just one ISO layer
1622 higher. If this option is specified all incoming and outgoing
1623 communication performed by a script is printed. The displayed
1624 information includes the communication protocol, the source, the
1625 target and the transmitted data. If more than 5% of all transmitted
1626 data is not printable, then the trace output is in a hex dump
1627 format. Specifying --packet-trace enables script tracing too.
1628 --script-updatedb
1630 This option updates the script database found in scripts/script.db
1631 which is used by Nmap to determine the available default scripts
1632 and categories. It is only necessary to update the database if you
1633 have added or removed NSE scripts from the default scripts
1634 directory or if you have changed the categories of any script. This
1635 option is generally used by itself: nmap --script-updatedb.
1636
1638 One of my highest Nmap development priorities has always been
1639 performance. A default scan (nmap hostname) of a host on my local
1640 network takes a fifth of a second. That is barely enough time to blink,
1641 but adds up when you are scanning hundreds or thousands of hosts.
1642 Moreover, certain scan options such as UDP scanning and version
1643 detection can increase scan times substantially. So can certain
1644 firewall configurations, particularly response rate limiting. While
1645 Nmap utilizes parallelism and many advanced algorithms to accelerate
1646 these scans, the user has ultimate control over how Nmap runs. Expert
1647 users carefully craft Nmap commands to obtain only the information they
1648 care about while meeting their time constraints.
1649 Techniques for improving scan times include omitting non-critical
1651 tests, and upgrading to the latest version of Nmap (performance
1652 enhancements are made frequently). Optimizing timing parameters can
1653 also make a substantial difference. Those options are listed below.
1654 Some options accept a time parameter. This is specified in seconds by
1656 default, though you can append ‘ms’, ‘s’, ‘m’, or ‘h’ to the value to
1657 specify milliseconds, seconds, minutes, or hours. So the --host-timeout
1658 arguments 900000ms, 900, 900s, and 15m all do the same thing.
1659 --min-hostgroup numhosts; --max-hostgroup numhosts (Adjust parallel
1661 scan group sizes)
1662 Nmap has the ability to port scan or version scan multiple hosts in
1663 parallel. Nmap does this by dividing the target IP space into
1664 groups and then scanning one group at a time. In general, larger
1665 groups are more efficient. The downside is that host results can't
1666 be provided until the whole group is finished. So if Nmap started
1667 out with a group size of 50, the user would not receive any reports
1668 (except for the updates offered in verbose mode) until the first 50
1669 hosts are completed.
1670 By default, Nmap takes a compromise approach to this conflict. It
1672 starts out with a group size as low as five so the first results
1673 come quickly and then increases the groupsize to as high as 1024.
1674 The exact default numbers depend on the options given. For
1675 efficiency reasons, Nmap uses larger group sizes for UDP or
1676 few-port TCP scans.
1677 When a maximum group size is specified with --max-hostgroup, Nmap
1679 will never exceed that size. Specify a minimum size with
1680 --min-hostgroup and Nmap will try to keep group sizes above that
1681 level. Nmap may have to use smaller groups than you specify if
1682 there are not enough target hosts left on a given interface to
1683 fulfill the specified minimum. Both may be set to keep the group
1684 size within a specific range, though this is rarely desired.
1685 These options do not have an effect during the host discovery phase
1687 of a scan. This includes plain ping scans (-sn). Host discovery
1688 always works in large groups of hosts to improve speed and
1689 accuracy.
1690 The primary use of these options is to specify a large minimum
1692 group size so that the full scan runs more quickly. A common choice
1693 is 256 to scan a network in /24 sized chunks. For a scan with many
1694 ports, exceeding that number is unlikely to help much. For scans of
1695 just a few port numbers, host group sizes of 2048 or more may be
1696 helpful.
1697 --min-parallelism numprobes; --max-parallelism numprobes (Adjust probe
1699 parallelization)
1700 These options control the total number of probes that may be
1701 outstanding for a host group. They are used for port scanning and
1702 host discovery. By default, Nmap calculates an ever-changing ideal
1703 parallelism based on network performance. If packets are being
1704 dropped, Nmap slows down and allows fewer outstanding probes. The
1705 ideal probe number slowly rises as the network proves itself
1706 worthy. These options place minimum or maximum bounds on that
1707 variable. By default, the ideal parallelism can drop to one if the
1708 network proves unreliable and rise to several hundred in perfect
1709 conditions.
1710 The most common usage is to set --min-parallelism to a number
1712 higher than one to speed up scans of poorly performing hosts or
1713 networks. This is a risky option to play with, as setting it too
1714 high may affect accuracy. Setting this also reduces Nmap's ability
1715 to control parallelism dynamically based on network conditions. A
1716 value of 10 might be reasonable, though I only adjust this value as
1717 a last resort.
1718 The --max-parallelism option is sometimes set to one to prevent
1720 Nmap from sending more than one probe at a time to hosts. The
1721 --scan-delay option, discussed later, is another way to do this.
1722 --min-rtt-timeout time, --max-rtt-timeout time, --initial-rtt-timeout
1724 time (Adjust probe timeouts)
1725 Nmap maintains a running timeout value for determining how long it
1726 will wait for a probe response before giving up or retransmitting
1727 the probe. This is calculated based on the response times of
1728 previous probes.
1729 If the network latency shows itself to be significant and variable,
1731 this timeout can grow to several seconds. It also starts at a
1732 conservative (high) level and may stay that way for a while when
1733 Nmap scans unresponsive hosts.
1734 Specifying a lower --max-rtt-timeout and --initial-rtt-timeout than
1736 the defaults can cut scan times significantly. This is particularly
1737 true for pingless (-Pn) scans, and those against heavily filtered
1738 networks. Don't get too aggressive though. The scan can end up
1739 taking longer if you specify such a low value that many probes are
1740 timing out and retransmitting while the response is in transit.
1741 If all the hosts are on a local network, 100 milliseconds
1743 (--max-rtt-timeout 100ms) is a reasonable aggressive value. If
1744 routing is involved, ping a host on the network first with the ICMP
1745 ping utility, or with a custom packet crafter such as Nping that is
1746 more likely to get through a firewall. Look at the maximum round
1747 trip time out of ten packets or so. You might want to double that
1748 for the --initial-rtt-timeout and triple or quadruple it for the
1749 --max-rtt-timeout. I generally do not set the maximum RTT below
1750 100 ms, no matter what the ping times are. Nor do I exceed 1000 ms.
1751 --min-rtt-timeout is a rarely used option that could be useful when
1753 a network is so unreliable that even Nmap's default is too
1754 aggressive. Since Nmap only reduces the timeout down to the minimum
1755 when the network seems to be reliable, this need is unusual and
1756 should be reported as a bug to the nmap-dev mailing list.
1757 --max-retries numtries (Specify the maximum number of port scan probe
1759 retransmissions)
1760 When Nmap receives no response to a port scan probe, it could mean
1761 the port is filtered. Or maybe the probe or response was simply
1762 lost on the network. It is also possible that the target host has
1763 rate limiting enabled that temporarily blocked the response. So
1764 Nmap tries again by retransmitting the initial probe. If Nmap
1765 detects poor network reliability, it may try many more times before
1766 giving up on a port. While this benefits accuracy, it also
1767 lengthens scan times. When performance is critical, scans may be
1768 sped up by limiting the number of retransmissions allowed. You can
1769 even specify --max-retries 0 to prevent any retransmissions, though
1770 that is only recommended for situations such as informal surveys
1771 where occasional missed ports and hosts are acceptable.
1772 The default (with no -T template) is to allow ten retransmissions.
1774 If a network seems reliable and the target hosts aren't rate
1775 limiting, Nmap usually only does one retransmission. So most target
1776 scans aren't even affected by dropping --max-retries to a low value
1777 such as three. Such values can substantially speed scans of slow
1778 (rate limited) hosts. You usually lose some information when Nmap
1779 gives up on ports early, though that may be preferable to letting
1780 the --host-timeout expire and losing all information about the
1781 target.
1782 --host-timeout time (Give up on slow target hosts)
1784 Some hosts simply take a long time to scan. This may be due to
1785 poorly performing or unreliable networking hardware or software,
1786 packet rate limiting, or a restrictive firewall. The slowest few
1787 percent of the scanned hosts can eat up a majority of the scan
1788 time. Sometimes it is best to cut your losses and skip those hosts
1789 initially. Specify --host-timeout with the maximum amount of time
1790 you are willing to wait. For example, specify 30m to ensure that
1791 Nmap doesn't waste more than half an hour on a single host. Note
1792 that Nmap may be scanning other hosts at the same time during that
1793 half an hour, so it isn't a complete loss. A host that times out is
1794 skipped. No port table, OS detection, or version detection results
1795 are printed for that host.
1796 The special value 0 can be used to mean “no timeout”, which can be
1798 used to override the T5 timing template, which sets the host
1799 timeout to 15 minutes.
1800 --script-timeout time
1802 While some scripts complete in fractions of a second, others can
1803 take hours or more depending on the nature of the script, arguments
1804 passed in, network and application conditions, and more. The
1805 --script-timeout option sets a ceiling on script execution time.
1806 Any script instance which exceeds that time will be terminated and
1807 no output will be shown. If debugging (-d) is enabled, Nmap will
1808 report on each timeout. For host and service scripts, a script
1809 instance only scans a single target host or port and the timeout
1810 period will be reset for the next instance.
1811 The special value 0 can be used to mean “no timeout”, which can be
1813 used to override the T5 timing template, which sets the script
1814 timeout to 10 minutes.
1815 --scan-delay time; --max-scan-delay time (Adjust delay between probes)
1817 This option causes Nmap to wait at least the given amount of time
1818 between each probe it sends to a given host. This is particularly
1819 useful in the case of rate limiting. Solaris machines (among many
1820 others) will usually respond to UDP scan probe packets with only
1821 one ICMP message per second. Any more than that sent by Nmap will
1822 be wasteful. A --scan-delay of 1s will keep Nmap at that slow rate.
1823 Nmap tries to detect rate limiting and adjust the scan delay
1824 accordingly, but it doesn't hurt to specify it explicitly if you
1825 already know what rate works best.
1826 When Nmap adjusts the scan delay upward to cope with rate limiting,
1828 the scan slows down dramatically. The --max-scan-delay option
1829 specifies the largest delay that Nmap will allow. A low
1830 --max-scan-delay can speed up Nmap, but it is risky. Setting this
1831 value too low can lead to wasteful packet retransmissions and
1832 possible missed ports when the target implements strict rate
1833 limiting.
1834 Another use of --scan-delay is to evade threshold based intrusion
1836 detection and prevention systems (IDS/IPS).
1837 --min-rate number; --max-rate number (Directly control the scanning
1839 rate)
1840 Nmap's dynamic timing does a good job of finding an appropriate
1841 speed at which to scan. Sometimes, however, you may happen to know
1842 an appropriate scanning rate for a network, or you may have to
1843 guarantee that a scan will be finished by a certain time. Or
1844 perhaps you must keep Nmap from scanning too quickly. The
1845 --min-rate and --max-rate options are designed for these
1846 situations.
1847 When the --min-rate option is given Nmap will do its best to send
1849 packets as fast as or faster than the given rate. The argument is a
1850 positive real number representing a packet rate in packets per
1851 second. For example, specifying --min-rate 300 means that Nmap will
1852 try to keep the sending rate at or above 300 packets per second.
1853 Specifying a minimum rate does not keep Nmap from going faster if
1854 conditions warrant.
1855 Likewise, --max-rate limits a scan's sending rate to a given
1857 maximum. Use --max-rate 100, for example, to limit sending to 100
1858 packets per second on a fast network. Use --max-rate 0.1 for a slow
1859 scan of one packet every ten seconds. Use --min-rate and --max-rate
1860 together to keep the rate inside a certain range.
1861 These two options are global, affecting an entire scan, not
1863 individual hosts. They only affect port scans and host discovery
1864 scans. Other features like OS detection implement their own timing.
1865 There are two conditions when the actual scanning rate may fall
1867 below the requested minimum. The first is if the minimum is faster
1868 than the fastest rate at which Nmap can send, which is dependent on
1869 hardware. In this case Nmap will simply send packets as fast as
1870 possible, but be aware that such high rates are likely to cause a
1871 loss of accuracy. The second case is when Nmap has nothing to send,
1872 for example at the end of a scan when the last probes have been
1873 sent and Nmap is waiting for them to time out or be responded to.
1874 It's normal to see the scanning rate drop at the end of a scan or
1875 in between hostgroups. The sending rate may temporarily exceed the
1876 maximum to make up for unpredictable delays, but on average the
1877 rate will stay at or below the maximum.
1878 Specifying a minimum rate should be done with care. Scanning faster
1880 than a network can support may lead to a loss of accuracy. In some
1881 cases, using a faster rate can make a scan take longer than it
1882 would with a slower rate. This is because Nmap's adaptive
1883 retransmission algorithms will detect the network congestion caused
1884 by an excessive scanning rate and increase the number of
1885 retransmissions in order to improve accuracy. So even though
1886 packets are sent at a higher rate, more packets are sent overall.
1887 Cap the number of retransmissions with the --max-retries option if
1888 you need to set an upper limit on total scan time.
1889 --defeat-rst-ratelimit
1891 Many hosts have long used rate limiting to reduce the number of
1892 ICMP error messages (such as port-unreachable errors) they send.
1893 Some systems now apply similar rate limits to the RST (reset)
1894 packets they generate. This can slow Nmap down dramatically as it
1895 adjusts its timing to reflect those rate limits. You can tell Nmap
1896 to ignore those rate limits (for port scans such as SYN scan which
1897 don't treat non-responsive ports as open) by specifying
1898 --defeat-rst-ratelimit.
1899 Using this option can reduce accuracy, as some ports will appear
1901 non-responsive because Nmap didn't wait long enough for a
1902 rate-limited RST response. With a SYN scan, the non-response
1903 results in the port being labeled filtered rather than the closed
1904 state we see when RST packets are received. This option is useful
1905 when you only care about open ports, and distinguishing between
1906 closed and filtered ports isn't worth the extra time.
1907 --defeat-icmp-ratelimit
1909 Similar to --defeat-rst-ratelimit, the --defeat-icmp-ratelimit
1910 option trades accuracy for speed, increasing UDP scanning speed
1911 against hosts that rate-limit ICMP error messages. Because this
1912 option causes Nmap to not delay in order to receive the port
1913 unreachable messages, a non-responsive port will be labeled
1914 closed|filtered instead of the default open|filtered. This has the
1915 effect of only treating ports which actually respond via UDP as
1916 open. Since many UDP services do not respond in this way, the
1917 chance for inaccuracy is greater with this option than with
1918 --defeat-rst-ratelimit.
1919 --nsock-engine iocp|epoll|kqueue|poll|select
1921 Enforce use of a given nsock IO multiplexing engine. Only the
1922 select(2)-based fallback engine is guaranteed to be available on
1923 your system. Engines are named after the name of the IO management
1924 facility they leverage. Engines currently implemented are epoll,
1925 kqueue, poll, and select, but not all will be present on any
1926 platform. By default, Nmap will use the "best" engine, i.e. the
1927 first one in this list that is supported. Use nmap -V to see which
1928 engines are supported on your platform.
1929 -T paranoid|sneaky|polite|normal|aggressive|insane (Set a timing
1931 template)
1932 While the fine-grained timing controls discussed in the previous
1933 section are powerful and effective, some people find them
1934 confusing. Moreover, choosing the appropriate values can sometimes
1935 take more time than the scan you are trying to optimize.
1936 Fortunately, Nmap offers a simpler approach, with six timing
1937 templates. You can specify them with the -T option and their number
1938 (0–5) or their name. The template names are paranoid (0),
1939 sneaky (1), polite (2), normal (3), aggressive (4), and insane (5).
1940 The first two are for IDS evasion. Polite mode slows down the scan
1941 to use less bandwidth and target machine resources. Normal mode is
1942 the default and so -T3 does nothing. Aggressive mode speeds scans
1943 up by making the assumption that you are on a reasonably fast and
1944 reliable network. Finally insane mode assumes that you are on an
1945 extraordinarily fast network or are willing to sacrifice some
1946 accuracy for speed.
1947 These templates allow the user to specify how aggressive they wish
1949 to be, while leaving Nmap to pick the exact timing values. The
1950 templates also make some minor speed adjustments for which
1951 fine-grained control options do not currently exist. For example,
1952 -T4 prohibits the dynamic scan delay from exceeding 10 ms for TCP
1953 ports and -T5 caps that value at 5 ms. Templates can be used in
1954 combination with fine-grained controls, and the fine-grained
1955 controls that you specify will take precedence over the timing
1956 template default for that parameter. I recommend using -T4 when
1957 scanning reasonably modern and reliable networks. Keep that option
1958 even when you add fine-grained controls so that you benefit from
1959 those extra minor optimizations that it enables.
1960 If you are on a decent broadband or ethernet connection, I would
1962 recommend always using -T4. Some people love -T5 though it is too
1963 aggressive for my taste. People sometimes specify -T2 because they
1964 think it is less likely to crash hosts or because they consider
1965 themselves to be polite in general. They often don't realize just
1966 how slow -T polite really is. Their scan may take ten times longer
1967 than a default scan. Machine crashes and bandwidth problems are
1968 rare with the default timing options (-T3) and so I normally
1969 recommend that for cautious scanners. Omitting version detection is
1970 far more effective than playing with timing values at reducing
1971 these problems.
1972 While -T0 and -T1 may be useful for avoiding IDS alerts, they will
1974 take an extraordinarily long time to scan thousands of machines or
1975 ports. For such a long scan, you may prefer to set the exact timing
1976 values you need rather than rely on the canned -T0 and -T1 values.
1977 The main effects of T0 are serializing the scan so only one port is
1979 scanned at a time, and waiting five minutes between sending each
1980 probe. T1 and T2 are similar but they only wait 15 seconds and 0.4
1981 seconds, respectively, between probes. T3 is Nmap's default
1982 behavior, which includes parallelization. -T4 does the equivalent
1983 of --max-rtt-timeout 1250ms --min-rtt-timeout 100ms
1984 --initial-rtt-timeout 500ms --max-retries 6 and sets the maximum
1985 TCP and SCTP scan delay to 10ms. T5 does the equivalent of
1986 --max-rtt-timeout 300ms --min-rtt-timeout 50ms
1987 --initial-rtt-timeout 250ms --max-retries 2 --host-timeout 15m
1988 --script-timeout 10m --max-scan-delay as well as setting the
1989 maximum TCP and SCTP scan delay to 5ms. Maximum UDP scan delay is
1990 not set by T4 or T5, but it can be set with the --max-scan-delay
1991 option.
1992
1994 Many Internet pioneers envisioned a global open network with a
1995 universal IP address space allowing virtual connections between any two
1996 nodes. This allows hosts to act as true peers, serving and retrieving
1997 information from each other. People could access all of their home
1998 systems from work, changing the climate control settings or unlocking
1999 the doors for early guests. This vision of universal connectivity has
2000 been stifled by address space shortages and security concerns. In the
2001 early 1990s, organizations began deploying firewalls for the express
2002 purpose of reducing connectivity. Huge networks were cordoned off from
2003 the unfiltered Internet by application proxies, network address
2004 translation, and packet filters. The unrestricted flow of information
2005 gave way to tight regulation of approved communication channels and the
2006 content that passes over them.
2007 Network obstructions such as firewalls can make mapping a network
2009 exceedingly difficult. It will not get any easier, as stifling casual
2010 reconnaissance is often a key goal of implementing the devices.
2011 Nevertheless, Nmap offers many features to help understand these
2012 complex networks, and to verify that filters are working as intended.
2013 It even supports mechanisms for bypassing poorly implemented defenses.
2014 One of the best methods of understanding your network security posture
2015 is to try to defeat it. Place yourself in the mind-set of an attacker,
2016 and deploy techniques from this section against your networks. Launch
2017 an FTP bounce scan, idle scan, fragmentation attack, or try to tunnel
2018 through one of your own proxies.
2019 In addition to restricting network activity, companies are increasingly
2021 monitoring traffic with intrusion detection systems (IDS). All of the
2022 major IDSs ship with rules designed to detect Nmap scans because scans
2023 are sometimes a precursor to attacks. Many of these products have
2024 recently morphed into intrusion prevention systems (IPS) that actively
2025 block traffic deemed malicious. Unfortunately for network
2026 administrators and IDS vendors, reliably detecting bad intentions by
2027 analyzing packet data is a tough problem. Attackers with patience,
2028 skill, and the help of certain Nmap options can usually pass by IDSs
2029 undetected. Meanwhile, administrators must cope with large numbers of
2030 false positive results where innocent activity is misdiagnosed and
2031 alerted on or blocked.
2032 Occasionally people suggest that Nmap should not offer features for
2034 evading firewall rules or sneaking past IDSs. They argue that these
2035 features are just as likely to be misused by attackers as used by
2036 administrators to enhance security. The problem with this logic is that
2037 these methods would still be used by attackers, who would just find
2038 other tools or patch the functionality into Nmap. Meanwhile,
2039 administrators would find it that much harder to do their jobs.
2040 Deploying only modern, patched FTP servers is a far more powerful
2041 defense than trying to prevent the distribution of tools implementing
2042 the FTP bounce attack.
2043 There is no magic bullet (or Nmap option) for detecting and subverting
2045 firewalls and IDS systems. It takes skill and experience. A tutorial is
2046 beyond the scope of this reference guide, which only lists the relevant
2047 options and describes what they do.
2048 -f (fragment packets); --mtu (using the specified MTU)
2050 The -f option causes the requested scan (including host discovery
2051 scans) to use tiny fragmented IP packets. The idea is to split up
2052 the TCP header over several packets to make it harder for packet
2053 filters, intrusion detection systems, and other annoyances to
2054 detect what you are doing. Be careful with this! Some programs have
2055 trouble handling these tiny packets. The old-school sniffer named
2056 Sniffit segmentation faulted immediately upon receiving the first
2057 fragment. Specify this option once, and Nmap splits the packets
2058 into eight bytes or less after the IP header. So a 20-byte TCP
2059 header would be split into three packets. Two with eight bytes of
2060 the TCP header, and one with the final four. Of course each
2061 fragment also has an IP header. Specify -f again to use 16 bytes
2062 per fragment (reducing the number of fragments). Or you can
2063 specify your own offset size with the --mtu option. Don't also
2064 specify -f if you use --mtu. The offset must be a multiple of
2065 eight. While fragmented packets won't get by packet filters and
2066 firewalls that queue all IP fragments, such as the
2067 CONFIG_IP_ALWAYS_DEFRAG option in the Linux kernel, some networks
2068 can't afford the performance hit this causes and thus leave it
2069 disabled. Others can't enable this because fragments may take
2070 different routes into their networks. Some source systems
2071 defragment outgoing packets in the kernel. Linux with the iptables
2072 connection tracking module is one such example. Do a scan while a
2073 sniffer such as Wireshark is running to ensure that sent packets
2074 are fragmented. If your host OS is causing problems, try the
2075 --send-eth option to bypass the IP layer and send raw ethernet
2076 frames.
2077 Fragmentation is only supported for Nmap's raw packet features,
2079 which includes TCP and UDP port scans (except connect scan and FTP
2080 bounce scan) and OS detection. Features such as version detection
2081 and the Nmap Scripting Engine generally don't support fragmentation
2082 because they rely on your host's TCP stack to communicate with
2083 target services.
2084 -D decoy1[,decoy2][,ME][,...] (Cloak a scan with decoys)
2086 Causes a decoy scan to be performed, which makes it appear to the
2087 remote host that the host(s) you specify as decoys are scanning the
2088 target network too. Thus their IDS might report 5–10 port scans
2089 from unique IP addresses, but they won't know which IP was scanning
2090 them and which were innocent decoys. While this can be defeated
2091 through router path tracing, response-dropping, and other active
2092 mechanisms, it is generally an effective technique for hiding your
2093 IP address.
2094 Separate each decoy host with commas, and you can optionally use ME
2096 as one of the decoys to represent the position for your real IP
2097 address. If you put ME in the sixth position or later, some common
2098 port scan detectors (such as Solar Designer's excellent Scanlogd)
2099 are unlikely to show your IP address at all. If you don't use ME,
2100 Nmap will put you in a random position. You can also use RND to
2101 generate a random, non-reserved IP address, or RND:number to
2102 generate number addresses.
2103 Note that the hosts you use as decoys should be up or you might
2105 accidentally SYN flood your targets. Also it will be pretty easy to
2106 determine which host is scanning if only one is actually up on the
2107 network. You might want to use IP addresses instead of names (so
2108 the decoy networks don't see you in their nameserver logs). Right
2109 now random IP address generation is only supported with IPv4
2110 Decoys are used both in the initial host discovery scan (using
2112 ICMP, SYN, ACK, or whatever) and during the actual port scanning
2113 phase. Decoys are also used during remote OS detection (-O). Decoys
2114 do not work with version detection or TCP connect scan. When a scan
2115 delay is in effect, the delay is enforced between each batch of
2116 spoofed probes, not between each individual probe. Because decoys
2117 are sent as a batch all at once, they may temporarily violate
2118 congestion control limits.
2119 It is worth noting that using too many decoys may slow your scan
2121 and potentially even make it less accurate. Also, some ISPs will
2122 filter out your spoofed packets, but many do not restrict spoofed
2123 IP packets at all.
2124 -S IP_Address (Spoof source address)
2126 In some circumstances, Nmap may not be able to determine your
2127 source address (Nmap will tell you if this is the case). In this
2128 situation, use -S with the IP address of the interface you wish to
2129 send packets through.
2130 Another possible use of this flag is to spoof the scan to make the
2132 targets think that someone else is scanning them. Imagine a company
2133 being repeatedly port scanned by a competitor! The -e option and
2134 -Pn are generally required for this sort of usage. Note that you
2135 usually won't receive reply packets back (they will be addressed to
2136 the IP you are spoofing), so Nmap won't produce useful reports.
2137 -e interface (Use specified interface)
2139 Tells Nmap what interface to send and receive packets on. Nmap
2140 should be able to detect this automatically, but it will tell you
2141 if it cannot.
2142 --source-port portnumber; -g portnumber (Spoof source port number)
2144 One surprisingly common misconfiguration is to trust traffic based
2145 only on the source port number. It is easy to understand how this
2146 comes about. An administrator will set up a shiny new firewall,
2147 only to be flooded with complaints from ungrateful users whose
2148 applications stopped working. In particular, DNS may be broken
2149 because the UDP DNS replies from external servers can no longer
2150 enter the network. FTP is another common example. In active FTP
2151 transfers, the remote server tries to establish a connection back
2152 to the client to transfer the requested file.
2153 Secure solutions to these problems exist, often in the form of
2155 application-level proxies or protocol-parsing firewall modules.
2156 Unfortunately there are also easier, insecure solutions. Noting
2157 that DNS replies come from port 53 and active FTP from port 20,
2158 many administrators have fallen into the trap of simply allowing
2159 incoming traffic from those ports. They often assume that no
2160 attacker would notice and exploit such firewall holes. In other
2161 cases, administrators consider this a short-term stop-gap measure
2162 until they can implement a more secure solution. Then they forget
2163 the security upgrade.
2164 Overworked network administrators are not the only ones to fall
2166 into this trap. Numerous products have shipped with these insecure
2167 rules. Even Microsoft has been guilty. The IPsec filters that
2168 shipped with Windows 2000 and Windows XP contain an implicit rule
2169 that allows all TCP or UDP traffic from port 88 (Kerberos). In
2170 another well-known case, versions of the Zone Alarm personal
2171 firewall up to 2.1.25 allowed any incoming UDP packets with the
2172 source port 53 (DNS) or 67 (DHCP).
2173 Nmap offers the -g and --source-port options (they are equivalent)
2175 to exploit these weaknesses. Simply provide a port number and Nmap
2176 will send packets from that port where possible. Most scanning
2177 operations that use raw sockets, including SYN and UDP scans,
2178 support the option completely. The option notably doesn't have an
2179 effect for any operations that use normal operating system sockets,
2180 including DNS requests, TCP connect scan, version detection, and
2181 script scanning. Setting the source port also doesn't work for OS
2182 detection, because Nmap must use different port numbers for certain
2183 OS detection tests to work properly.
2184 --data hex string (Append custom binary data to sent packets)
2186 This option lets you include binary data as payload in sent
2187 packets. hex string may be specified in any of the following
2188 formats: 0xAABBCCDDEEFF..., AABBCCDDEEFF... or
2189 \xAA\xBB\xCC\xDD\xEE\xFF.... Examples of use are --data 0xdeadbeef
2190 and --data \xCA\xFE\x09. Note that if you specify a number like
2191 0x00ff no byte-order conversion is performed. Make sure you specify
2192 the information in the byte order expected by the receiver.
2193 --data-string string (Append custom string to sent packets)
2195 This option lets you include a regular string as payload in sent
2196 packets. string can contain any string. However, note that some
2197 characters may depend on your system's locale and the receiver may
2198 not see the same information. Also, make sure you enclose the
2199 string in double quotes and escape any special characters from the
2200 shell. Examples: --data-string "Scan conducted by Security Ops,
2201 extension 7192" or --data-string "Ph34r my l33t skills". Keep in
2202 mind that nobody is likely to actually see any comments left by
2203 this option unless they are carefully monitoring the network with a
2204 sniffer or custom IDS rules.
2205 --data-length number (Append random data to sent packets)
2207 Normally Nmap sends minimalist packets containing only a header. So
2208 its TCP packets are generally 40 bytes and ICMP echo requests are
2209 just 28. Some UDP ports and IP protocols get a custom payload by
2210 default. This option tells Nmap to append the given number of
2211 random bytes to most of the packets it sends, and not to use any
2212 protocol-specific payloads. (Use --data-length 0 for no random or
2213 protocol-specific payloads. OS detection (-O) packets are not
2214 affected because accuracy there requires probe consistency, but
2215 most pinging and portscan packets support this. It slows things
2216 down a little, but can make a scan slightly less conspicuous.
2217 --ip-options S|R [route]|L [route]|T|U ... ; --ip-options hex string
2219 (Send packets with specified ip options)
2220 The IP protocol[12] offers several options which may be placed in
2221 packet headers. Unlike the ubiquitous TCP options, IP options are
2222 rarely seen due to practicality and security concerns. In fact,
2223 many Internet routers block the most dangerous options such as
2224 source routing. Yet options can still be useful in some cases for
2225 determining and manipulating the network route to target machines.
2226 For example, you may be able to use the record route option to
2227 determine a path to a target even when more traditional
2228 traceroute-style approaches fail. Or if your packets are being
2229 dropped by a certain firewall, you may be able to specify a
2230 different route with the strict or loose source routing options.
2231 The most powerful way to specify IP options is to simply pass in
2233 values as the argument to --ip-options. Precede each hex number
2234 with \x then the two digits. You may repeat certain characters by
2235 following them with an asterisk and then the number of times you
2236 wish them to repeat. For example, \x01\x07\x04\x00*36\x01 is a hex
2237 string containing 36 NUL bytes.
2238 Nmap also offers a shortcut mechanism for specifying options.
2240 Simply pass the letter R, T, or U to request record-route,
2241 record-timestamp, or both options together, respectively. Loose or
2242 strict source routing may be specified with an L or S followed by a
2243 space and then a space-separated list of IP addresses.
2244 If you wish to see the options in packets sent and received,
2246 specify --packet-trace. For more information and examples of using
2247 IP options with Nmap, see http://seclists.org/nmap-dev/2006/q3/52.
2248 --ttl value (Set IP time-to-live field)
2250 Sets the IPv4 time-to-live field in sent packets to the given
2251 value.
2252 --randomize-hosts (Randomize target host order)
2254 Tells Nmap to shuffle each group of up to 16384 hosts before it
2255 scans them. This can make the scans less obvious to various network
2256 monitoring systems, especially when you combine it with slow timing
2257 options. If you want to randomize over larger group sizes, increase
2258 PING_GROUP_SZ in nmap.h and recompile. An alternative solution is
2259 to generate the target IP list with a list scan (-sL -n -oN
2260 filename), randomize it with a Perl script, then provide the whole
2261 list to Nmap with -iL.
2262 --spoof-mac MAC address, prefix, or vendor name (Spoof MAC address)
2264 Asks Nmap to use the given MAC address
2265 for all of the raw ethernet frames it sends. This option implies
2267 --send-eth to ensure that Nmap actually sends ethernet-level
2268 packets. The MAC given can take several formats. If it is simply
2269 the number 0, Nmap chooses a completely random MAC address for the
2270 session. If the given string is an even number of hex digits (with
2271 the pairs optionally separated by a colon), Nmap will use those as
2272 the MAC. If fewer than 12 hex digits are provided, Nmap fills in
2273 the remainder of the six bytes with random values. If the argument
2274 isn't a zero or hex string, Nmap looks through nmap-mac-prefixes to
2275 find a vendor name containing the given string (it is case
2276 insensitive). If a match is found, Nmap uses the vendor's OUI
2277 (three-byte prefix) and fills out the remaining three bytes
2278 randomly. Valid --spoof-mac argument examples are Apple, 0,
2279 01:02:03:04:05:06, deadbeefcafe, 0020F2, and Cisco. This option
2280 only affects raw packet scans such as SYN scan or OS detection, not
2281 connection-oriented features such as version detection or the Nmap
2282 Scripting Engine.
2283 --proxies Comma-separated list of proxy URLs (Relay TCP connections
2285 through a chain of proxies)
2286 Asks Nmap to establish TCP connections with a final target through
2287 supplied chain of one or more HTTP or SOCKS4 proxies. Proxies can
2288 help hide the true source of a scan or evade certain firewall
2289 restrictions, but they can hamper scan performance by increasing
2290 latency. Users may need to adjust Nmap timeouts and other scan
2291 parameters accordingly. In particular, a lower --max-parallelism
2292 may help because some proxies refuse to handle as many concurrent
2293 connections as Nmap opens by default.
2294 This option takes a list of proxies as argument, expressed as URLs
2296 in the format proto://host:port. Use commas to separate node URLs
2297 in a chain. No authentication is supported yet. Valid protocols are
2298 HTTP and SOCKS4.
2299 Warning: this feature is still under development and has
2301 limitations. It is implemented within the nsock library and thus
2302 has no effect on the ping, port scanning and OS discovery phases of
2303 a scan. Only NSE and version scan benefit from this option so far—
2304 other features may disclose your true address. SSL connections are
2305 not yet supported, nor is proxy-side DNS resolution (hostnames are
2306 always resolved by Nmap).
2307 --badsum (Send packets with bogus TCP/UDP checksums)
2309 Asks Nmap to use an invalid TCP, UDP or SCTP checksum for packets
2310 sent to target hosts. Since virtually all host IP stacks properly
2311 drop these packets, any responses received are likely coming from a
2312 firewall or IDS that didn't bother to verify the checksum. For more
2313 details on this technique, see https://nmap.org/p60-12.html
2314 --adler32 (Use deprecated Adler32 instead of CRC32C for SCTP checksums)
2316 Asks Nmap to use the deprecated Adler32 algorithm for calculating
2317 the SCTP checksum. If --adler32 is not given, CRC-32C (Castagnoli)
2318 is used. RFC 2960[13] originally defined Adler32 as checksum
2319 algorithm for SCTP; RFC 4960[6] later redefined the SCTP checksums
2320 to use CRC-32C. Current SCTP implementations should be using
2321 CRC-32C, but in order to elicit responses from old, legacy SCTP
2322 implementations, it may be preferable to use Adler32.
2323
2325 Any security tool is only as useful as the output it generates. Complex
2326 tests and algorithms are of little value if they aren't presented in an
2327 organized and comprehensible fashion. Given the number of ways Nmap is
2328 used by people and other software, no single format can please
2329 everyone. So Nmap offers several formats, including the interactive
2330 mode for humans to read directly and XML for easy parsing by software.
2331 In addition to offering different output formats, Nmap provides options
2333 for controlling the verbosity of output as well as debugging messages.
2334 Output types may be sent to standard output or to named files, which
2335 Nmap can append to or clobber. Output files may also be used to resume
2336 aborted scans.
2337 Nmap makes output available in five different formats. The default is
2339 called interactive output, and it is sent to standard output (stdout).
2340 There is also normal output, which is similar to interactive except
2341 that it displays less runtime information and warnings since it is
2342 expected to be analyzed after the scan completes rather than
2343 interactively.
2344 XML output is one of the most important output types, as it can be
2346 converted to HTML, easily parsed by programs such as Nmap graphical
2347 user interfaces, or imported into databases.
2348 The two remaining output types are the simple grepable output which
2350 includes most information for a target host on a single line, and
2351 sCRiPt KiDDi3 0utPUt for users who consider themselves |<-r4d.
2352 While interactive output is the default and has no associated
2354 command-line options, the other four format options use the same
2355 syntax. They take one argument, which is the filename that results
2356 should be stored in. Multiple formats may be specified, but each format
2357 may only be specified once. For example, you may wish to save normal
2358 output for your own review while saving XML of the same scan for
2359 programmatic analysis. You might do this with the options -oX
2360 myscan.xml -oN myscan.nmap. While this chapter uses the simple names
2361 like myscan.xml for brevity, more descriptive names are generally
2362 recommended. The names chosen are a matter of personal preference,
2363 though I use long ones that incorporate the scan date and a word or two
2364 describing the scan, placed in a directory named after the company I'm
2365 scanning.
2366 While these options save results to files, Nmap still prints
2368 interactive output to stdout as usual. For example, the command nmap
2369 -oX myscan.xml target prints XML to myscan.xml and fills standard
2370 output with the same interactive results it would have printed if -oX
2371 wasn't specified at all. You can change this by passing a hyphen
2372 character as the argument to one of the format types. This causes Nmap
2373 to deactivate interactive output, and instead print results in the
2374 format you specified to the standard output stream. So the command nmap
2375 -oX - target will send only XML output to stdout. Serious errors may
2376 still be printed to the normal error stream, stderr.
2377 Unlike some Nmap arguments, the space between the logfile option flag
2379 (such as -oX) and the filename or hyphen is mandatory. If you omit the
2380 flags and give arguments such as -oG- or -oXscan.xml, a backwards
2381 compatibility feature of Nmap will cause the creation of normal format
2382 output files named G- and Xscan.xml respectively.
2383 All of these arguments support strftime-like conversions in the
2385 filename. %H, %M, %S, %m, %d, %y, and %Y are all exactly the same as
2386 in strftime. %T is the same as %H%M%S, %R is the same as %H%M, and %D
2387 is the same as %m%d%y. A % followed by any other character just yields
2388 that character (%% gives you a percent symbol). So -oX 'scan-%T-%D.xml'
2389 will use an XML file with a name in the form of scan-144840-121307.xml.
2390 Nmap also offers options to control scan verbosity and to append to
2392 output files rather than clobbering them. All of these options are
2393 described below.
2394 Nmap Output Formats
2396 -oN filespec (normal output)
2398 Requests that normal output be directed to the given filename. As
2399 discussed above, this differs slightly from interactive output.
2400 -oX filespec (XML output)
2402 Requests that XML output be directed to the given filename. Nmap
2403 includes a document type definition (DTD) which allows XML parsers
2404 to validate Nmap XML output. While it is primarily intended for
2405 programmatic use, it can also help humans interpret Nmap XML
2406 output. The DTD defines the legal elements of the format, and often
2407 enumerates the attributes and values they can take on. The latest
2408 version is always available from
2409 https://svn.nmap.org/nmap/docs/nmap.dtd.
2410 XML offers a stable format that is easily parsed by software. Free
2412 XML parsers are available for all major computer languages,
2413 including C/C++, Perl, Python, and Java. People have even written
2414 bindings for most of these languages to handle Nmap output and
2415 execution specifically. Examples are Nmap::Scanner[14] and
2416 Nmap::Parser[15] in Perl CPAN. In almost all cases that a
2417 non-trivial application interfaces with Nmap, XML is the preferred
2418 format.
2419 The XML output references an XSL stylesheet which can be used to
2421 format the results as HTML. The easiest way to use this is simply
2422 to load the XML output in a web browser such as Firefox or IE. By
2423 default, this will only work on the machine you ran Nmap on (or a
2424 similarly configured one) due to the hard-coded nmap.xsl filesystem
2425 path. Use the --webxml or --stylesheet options to create portable
2426 XML files that render as HTML on any web-connected machine.
2427 -oS filespec (ScRipT KIdd|3 oUTpuT)
2429 Script kiddie output is like interactive output, except that it is
2430 post-processed to better suit the l33t HaXXorZ who previously
2431 looked down on Nmap due to its consistent capitalization and
2432 spelling. Humor impaired people should note that this option is
2433 making fun of the script kiddies before flaming me for supposedly
2434 “helping them”.
2435 -oG filespec (grepable output)
2437 This output format is covered last because it is deprecated. The
2438 XML output format is far more powerful, and is nearly as convenient
2439 for experienced users. XML is a standard for which dozens of
2440 excellent parsers are available, while grepable output is my own
2441 simple hack. XML is extensible to support new Nmap features as they
2442 are released, while I often must omit those features from grepable
2443 output for lack of a place to put them.
2444 Nevertheless, grepable output is still quite popular. It is a
2446 simple format that lists each host on one line and can be trivially
2447 searched and parsed with standard Unix tools such as grep, awk,
2448 cut, sed, diff, and Perl. Even I usually use it for one-off tests
2449 done at the command line. Finding all the hosts with the SSH port
2450 open or that are running Solaris takes only a simple grep to
2451 identify the hosts, piped to an awk or cut command to print the
2452 desired fields.
2453 Grepable output consists of comments (lines starting with a pound
2455 (#)) and target lines. A target line includes a combination of six
2456 labeled fields, separated by tabs and followed with a colon. The
2457 fields are Host, Ports, Protocols, Ignored State, OS, Seq Index, IP
2458 ID, and Status.
2459 The most important of these fields is generally Ports, which gives
2461 details on each interesting port. It is a comma separated list of
2462 port entries. Each port entry represents one interesting port, and
2463 takes the form of seven slash (/) separated subfields. Those
2464 subfields are: Port number, State, Protocol, Owner, Service, SunRPC
2465 info, and Version info.
2466 As with XML output, this man page does not allow for documenting
2468 the entire format. A more detailed look at the Nmap grepable output
2469 format is available from
2470 https://nmap.org/book/output-formats-grepable-output.html.
2471 -oA basename (Output to all formats)
2473 As a convenience, you may specify -oA basename to store scan
2474 results in normal, XML, and grepable formats at once. They are
2475 stored in basename.nmap, basename.xml, and basename.gnmap,
2476 respectively. As with most programs, you can prefix the filenames
2477 with a directory path, such as ~/nmaplogs/foocorp/ on Unix or
2478 c:\hacking\sco on Windows.
2479 Verbosity and debugging options
2481 -v (Increase verbosity level), -vlevel (Set verbosity level)
2483 Increases the verbosity level, causing Nmap to print more
2484 information about the scan in progress. Open ports are shown as
2485 they are found and completion time estimates are provided when Nmap
2486 thinks a scan will take more than a few minutes. Use it twice or
2487 more for even greater verbosity: -vv, or give a verbosity level
2488 directly, for example -v3.
2489 Most changes only affect interactive output, and some also affect
2491 normal and script kiddie output. The other output types are meant
2492 to be processed by machines, so Nmap can give substantial detail by
2493 default in those formats without fatiguing a human user. However,
2494 there are a few changes in other modes where output size can be
2495 reduced substantially by omitting some detail. For example, a
2496 comment line in the grepable output that provides a list of all
2497 ports scanned is only printed in verbose mode because it can be
2498 quite long.
2499 -d (Increase debugging level), -dlevel (Set debugging level)
2501 When even verbose mode doesn't provide sufficient data for you,
2502 debugging is available to flood you with much more! As with the
2503 verbosity option (-v), debugging is enabled with a command-line
2504 flag (-d) and the debug level can be increased by specifying it
2505 multiple times, as in -dd, or by setting a level directly. For
2506 example, -d9 sets level nine. That is the highest effective level
2507 and will produce thousands of lines unless you run a very simple
2508 scan with very few ports and targets.
2509 Debugging output is useful when a bug is suspected in Nmap, or if
2511 you are simply confused as to what Nmap is doing and why. As this
2512 feature is mostly intended for developers, debug lines aren't
2513 always self-explanatory. You may get something like: Timeout vals:
2514 srtt: -1 rttvar: -1 to: 1000000 delta 14987 ==> srtt: 14987 rttvar:
2515 14987 to: 100000. If you don't understand a line, your only
2516 recourses are to ignore it, look it up in the source code, or
2517 request help from the development list (nmap-dev). Some lines are
2518 self explanatory, but the messages become more obscure as the debug
2519 level is increased.
2520 --reason (Host and port state reasons)
2522 Shows the reason each port is set to a specific state and the
2523 reason each host is up or down. This option displays the type of
2524 the packet that determined a port or hosts state. For example, A
2525 RST packet from a closed port or an echo reply from an alive host.
2526 The information Nmap can provide is determined by the type of scan
2527 or ping. The SYN scan and SYN ping (-sS and -PS) are very detailed,
2528 but the TCP connect scan (-sT) is limited by the implementation of
2529 the connect system call. This feature is automatically enabled by
2530 the debug option (-d) and the results are stored in XML log files
2531 even if this option is not specified.
2532 --stats-every time (Print periodic timing stats)
2534 Periodically prints a timing status message after each interval of
2535 time. The time is a specification of the kind described in the
2536 section called “TIMING AND PERFORMANCE”; so for example, use
2537 --stats-every 10s to get a status update every 10 seconds. Updates
2538 are printed to interactive output (the screen) and XML output.
2539 --packet-trace (Trace packets and data sent and received)
2541 Causes Nmap to print a summary of every packet sent or received.
2542 This is often used for debugging, but is also a valuable way for
2543 new users to understand exactly what Nmap is doing under the
2544 covers. To avoid printing thousands of lines, you may want to
2545 specify a limited number of ports to scan, such as -p20-30. If you
2546 only care about the goings on of the version detection subsystem,
2547 use --version-trace instead. If you only care about script tracing,
2548 specify --script-trace. With --packet-trace, you get all of the
2549 above.
2550 --open (Show only open (or possibly open) ports)
2552 Sometimes you only care about ports you can actually connect to
2553 (open ones), and don't want results cluttered with closed,
2554 filtered, and closed|filtered ports. Output customization is
2555 normally done after the scan using tools such as grep, awk, and
2556 Perl, but this feature was added due to overwhelming requests.
2557 Specify --open to only see hosts with at least one open,
2558 open|filtered, or unfiltered port, and only see ports in those
2559 states. These three states are treated just as they normally are,
2560 which means that open|filtered and unfiltered may be condensed into
2561 counts if there are an overwhelming number of them.
2562 Beginning with Nmap 7.40, the --open option implies
2564 --defeat-rst-ratelimit, because that option only affects closed and
2566 filtered ports, which are hidden by --open.
2567 --iflist (List interfaces and routes)
2569 Prints the interface list and system routes as detected by Nmap and
2570 quits. 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 scan output files were kept, the
2594 user can ask Nmap to resume scanning with the target it was working
2595 on when execution ceased. Simply specify the --resume option and
2596 pass the output file as its argument. No other arguments are
2597 permitted, as Nmap parses the output file to use the same ones
2598 specified previously. Simply call Nmap as nmap --resume
2599 logfilename. Nmap will append new results to the data files
2600 specified in the previous execution. Scans can be resumed from any
2601 of the 3 major output formats: Normal, Grepable, or XML
2602 --noninteractive (Disable runtime interactions)
2604 At times, such as when running Nmap in a shell background, it might
2605 be undesirable for Nmap to monitor and respond to user keyboard
2606 input when running. (See the section called “RUNTIME INTERACTION”
2607 about how to control Nmap during a scan.) Use option
2608 --noninteractive to prevent Nmap taking control of the terminal.
2609 --stylesheet path or URL (Set XSL stylesheet to transform XML output)
2611 Nmap ships with an XSL stylesheet named nmap.xsl for viewing or
2612 translating XML output to HTML. The XML output includes an
2613 xml-stylesheet directive which points to nmap.xml where it was
2614 initially installed by Nmap. Run the XML file through an XSLT
2615 processor such as xsltproc[16] to produce an HTML file. Directly
2616 opening the XML file in a browser no longer works well because
2617 modern browsers limit the locations a stylesheet may be loaded
2618 from. If you wish to use a different stylesheet, specify it as the
2619 argument to --stylesheet. You must pass the full pathname or URL.
2620 One common invocation is --stylesheet
2621 https://nmap.org/svn/docs/nmap.xsl. This tells an XSLT processor to
2622 load the latest version of the stylesheet from Nmap.Org. The
2623 --webxml option does the same thing with less typing and
2624 memorization. Loading the XSL from Nmap.Org makes it easier to view
2625 results on a machine that doesn't have Nmap (and thus nmap.xsl)
2626 installed. So the URL is often more useful, but the local
2627 filesystem location of nmap.xsl is used by default for privacy
2628 reasons.
2629 --webxml (Load stylesheet from Nmap.Org)
2631 This is a convenience option, nothing more than an alias for
2632 --stylesheet https://nmap.org/svn/docs/nmap.xsl.
2633 --no-stylesheet (Omit XSL stylesheet declaration from XML)
2635 Specify this option to prevent Nmap from associating any XSL
2636 stylesheet with its XML output. The xml-stylesheet directive is
2637 omitted.
2638
2640 This section describes some important (and not-so-important) options
2641 that don't really fit anywhere else.
2642 -6 (Enable IPv6 scanning)
2644 Nmap has IPv6 support for its most popular features. Ping scanning,
2645 port scanning, version detection, and the Nmap Scripting Engine all
2646 support IPv6. The command syntax is the same as usual except that
2647 you also add the -6 option. Of course, you must use IPv6 syntax if
2648 you specify an address rather than a hostname. An address might
2649 look like 3ffe:7501:4819:2000:210:f3ff:fe03:14d0, so hostnames are
2650 recommended. The output looks the same as usual, with the IPv6
2651 address on the “interesting ports” line being the only IPv6
2652 giveaway.
2653 While IPv6 hasn't exactly taken the world by storm, it gets
2655 significant use in some (usually Asian) countries and most modern
2656 operating systems support it. To use Nmap with IPv6, both the
2657 source and target of your scan must be configured for IPv6. If your
2658 ISP (like most of them) does not allocate IPv6 addresses to you,
2659 free tunnel brokers are widely available and work fine with Nmap. I
2660 use the free IPv6 tunnel broker service at
2661 http://www.tunnelbroker.net. Other tunnel brokers are listed at
2662 Wikipedia[17]. 6to4 tunnels are another popular, free approach.
2663 On Windows, raw-socket IPv6 scans are supported only on ethernet
2665 devices (not tunnels), and only on Windows Vista and later. Use the
2666 --unprivileged option in other situations.
2667 -A (Aggressive scan options)
2669 This option enables additional advanced and aggressive options.
2670 Presently this enables OS detection (-O), version scanning (-sV),
2671 script scanning (-sC) and traceroute (--traceroute). More features
2672 may be added in the future. The point is to enable a comprehensive
2673 set of scan options without people having to remember a large set
2674 of flags. However, because script scanning with the default set is
2675 considered intrusive, you should not use -A against target networks
2676 without permission. This option only enables features, and not
2677 timing options (such as -T4) or verbosity options (-v) that you
2678 might want as well. Options which require privileges (e.g. root
2679 access) such as OS detection and traceroute will only be enabled if
2680 those privileges are available.
2681 --datadir directoryname (Specify custom Nmap data file location)
2683 Nmap obtains some special data at runtime in files named
2684 nmap-service-probes, nmap-services, nmap-protocols, nmap-rpc,
2685 nmap-mac-prefixes, and nmap-os-db. If the location of any of these
2686 files has been specified (using the --servicedb or --versiondb
2687 options), that location is used for that file. After that, Nmap
2688 searches these files in the directory specified with the --datadir
2689 option (if any). Any files not found there, are searched for in the
2690 directory specified by the NMAPDIR environment variable. Next comes
2691 ~/.nmap for real and effective UIDs; or on Windows,
2692 HOME\AppData\Roaming\nmap (where HOME is the user's home directory,
2693 like C:\Users\user). This is followed by the location of the nmap
2694 executable and the same location with ../share/nmap appended. Then
2695 a compiled-in location such as /usr/local/share/nmap or
2696 /usr/share/nmap.
2697 --servicedb services file (Specify custom services file)
2699 Asks Nmap to use the specified services file rather than the
2700 nmap-services data file that comes with Nmap. Using this option
2701 also causes a fast scan (-F) to be used. See the description for
2702 --datadir for more information on Nmap's data files.
2703 --versiondb service probes file (Specify custom service probes file)
2705 Asks Nmap to use the specified service probes file rather than the
2706 nmap-service-probes data file that comes with Nmap. See the
2707 description for --datadir for more information on Nmap's data
2708 files.
2709 --send-eth (Use raw ethernet sending)
2711 Asks Nmap to send packets at the raw ethernet (data link) layer
2712 rather than the higher IP (network) layer. By default, Nmap chooses
2713 the one which is generally best for the platform it is running on.
2714 Raw sockets (IP layer) are generally most efficient for Unix
2715 machines, while ethernet frames are required for Windows operation
2716 since Microsoft disabled raw socket support. Nmap still uses raw IP
2717 packets on Unix despite this option when there is no other choice
2718 (such as non-ethernet connections).
2719 --send-ip (Send at raw IP level)
2721 Asks Nmap to send packets via raw IP sockets rather than sending
2722 lower level ethernet frames. It is the complement to the --send-eth
2723 option discussed previously.
2724 --privileged (Assume that the user is fully privileged)
2726 Tells Nmap to simply assume that it is privileged enough to perform
2727 raw socket sends, packet sniffing, and similar operations that
2728 usually require root privileges on Unix systems. By default Nmap
2729 quits if such operations are requested but geteuid is not zero.
2730 --privileged is useful with Linux kernel capabilities and similar
2731 systems that may be configured to allow unprivileged users to
2732 perform raw-packet scans. Be sure to provide this option flag
2733 before any flags for options that require privileges (SYN scan, OS
2734 detection, etc.). The NMAP_PRIVILEGED environment variable may be
2735 set as an equivalent alternative to --privileged.
2736 --unprivileged (Assume that the user lacks raw socket privileges)
2738 This option is the opposite of --privileged. It tells Nmap to treat
2739 the user as lacking network raw socket and sniffing privileges.
2740 This is useful for testing, debugging, or when the raw network
2741 functionality of your operating system is somehow broken. The
2742 NMAP_UNPRIVILEGED environment variable may be set as an equivalent
2743 alternative to --unprivileged.
2744 --release-memory (Release memory before quitting)
2746 This option is only useful for memory-leak debugging. It causes
2747 Nmap to release allocated memory just before it quits so that
2748 actual memory leaks are easier to spot. Normally Nmap skips this as
2749 the OS does this anyway upon process termination.
2750 -V; --version (Print version number)
2752 Prints the Nmap version number and exits.
2753 -h; --help (Print help summary page)
2755 Prints a short help screen with the most common command flags.
2756 Running Nmap without any arguments does the same thing.
2757
2759 During the execution of Nmap, all key presses are captured. This allows
2760 you to interact with the program without aborting and restarting it.
2761 Certain special keys will change options, while any other keys will
2762 print out a status message telling you about the scan. The convention
2763 is that lowercase letters increase the amount of printing, and
2764 uppercase letters decrease the printing. You may also press ‘?’ for
2765 help.
2766 v / V
2768 Increase / decrease the verbosity level
2769 d / D
2771 Increase / decrease the debugging Level
2772 p / P
2774 Turn on / off packet tracing
2775 ?
2777 Print a runtime interaction help screen
2778 Anything else
2780 Print out a status message like this:
2781 Stats: 0:00:07 elapsed; 20 hosts completed (1 up), 1 undergoing Service Scan
2783 Service scan Timing: About 33.33% done; ETC: 20:57 (0:00:12 remaining)
2784
2786 Here are some Nmap usage examples, from the simple and routine to a
2787 little more complex and esoteric. Some actual IP addresses and domain
2788 names are used to make things more concrete. In their place you should
2789 substitute addresses/names from your own network. While I don't think
2790 port scanning other networks is or should be illegal, some network
2791 administrators don't appreciate unsolicited scanning of their networks
2792 and may complain. Getting permission first is the best approach.
2793 For testing purposes, you have permission to scan the host
2795 scanme.nmap.org. This permission only includes scanning via Nmap and
2796 not testing exploits or denial of service attacks. To conserve
2797 bandwidth, please do not initiate more than a dozen scans against that
2798 host per day. If this free scanning target service is abused, it will
2799 be taken down and Nmap will report Failed to resolve given hostname/IP:
2800 scanme.nmap.org. These permissions also apply to the hosts
2801 scanme2.nmap.org, scanme3.nmap.org, and so on, though those hosts do
2802 not currently exist.
2803 nmap -v scanme.nmap.org
2805 This option scans all reserved TCP ports on the machine scanme.nmap.org
2807 . The -v option enables verbose mode.
2808 nmap -sS -O scanme.nmap.org/24
2810 Launches a stealth SYN scan against each machine that is up out of the
2813 256 IPs on the /24 sized network where Scanme resides. It also tries to
2814 determine what operating system is running on each host that is up and
2815 running. This requires root privileges because of the SYN scan and OS
2816 detection.
2817 nmap -sV -p 22,53,110,143,4564 198.116.0-255.1-127
2819 Launches host enumeration and a TCP scan at the first half of each of
2821 the 255 possible eight-bit subnets in the 198.116.0.0/16 address space.
2822 This tests whether the systems run SSH, DNS, POP3, or IMAP on their
2823 standard ports, or anything on port 4564. For any of these ports found
2824 open, version detection is used to determine what application is
2825 running.
2826 nmap -v -iR 100000 -Pn -p 80
2828 Asks Nmap to choose 100,000 hosts at random and scan them for web
2831 servers (port 80). Host enumeration is disabled with -Pn since first
2832 sending a couple probes to determine whether a host is up is wasteful
2833 when you are only probing one port on each target host anyway.
2834 nmap -Pn -p80 -oX logs/pb-port80scan.xml -oG logs/pb-port80scan.gnmap
2836 216.163.128.20/20
2837 This scans 4096 IPs for any web servers (without pinging them) and
2840 saves the output in grepable and XML formats.
2841
2843 While this reference guide details all material Nmap options, it can't
2844 fully demonstrate how to apply those features to quickly solve
2845 real-world tasks. For that, we released Nmap Network Scanning: The
2846 Official Nmap Project Guide to Network Discovery and Security Scanning.
2847 Topics include subverting firewalls and intrusion detection systems,
2848 optimizing Nmap performance, and automating common networking tasks
2849 with the Nmap Scripting Engine. Hints and instructions are provided for
2850 common Nmap tasks such as taking network inventory, penetration
2851 testing, detecting rogue wireless access points, and quashing network
2852 worm outbreaks. Examples and diagrams show actual communication on the
2853 wire. More than half of the book is available free online. See
2854 https://nmap.org/book for more information.
2855
2857 Like its author, Nmap isn't perfect. But you can help make it better by
2858 sending bug reports or even writing patches. If Nmap doesn't behave the
2859 way you expect, first upgrade to the latest version available from
2860 https://nmap.org. If the problem persists, do some research to
2861 determine whether it has already been discovered and addressed. Try
2862 searching for the problem or error message on Google since that
2863 aggregates so many forums. If nothing comes of this, create an Issue on
2864 our tracker (http://issues.nmap.org) and/or mail a bug report to
2865 <dev@nmap.org>. If you subscribe to the nmap-dev list before posting,
2866 your message will bypass moderation and get through more quickly.
2867 Subscribe at https://nmap.org/mailman/listinfo/dev. Please include
2868 everything you have learned about the problem, as well as what version
2869 of Nmap you are using and what operating system version it is running
2870 on. Other suggestions for improving Nmap may be sent to the Nmap dev
2871 mailing list as well.
2872 If you are able to write a patch improving Nmap or fixing a bug, that
2874 is even better! Instructions for submitting patches or git pull
2875 requests are available from
2876 https://github.com/nmap/nmap/blob/master/CONTRIBUTING.md
2877 Particularly sensitive issues such as a security reports may be sent
2879 directly to Nmap's author Fyodor directly at <fyodor@nmap.org>. All
2880 other reports and comments should use the dev list or issue tracker
2881 instead because more people read, follow, and respond to those.
2882
2884 Gordon “Fyodor” Lyon <fyodor@nmap.org> wrote and released Nmap in 1997.
2885 Since then, hundreds of people have made valuable contributions, as
2886 detailed in the CHANGELOG file distributed with Nmap and also available
2887 from https://nmap.org/changelog.html. David Fifield and Daniel Miller
2888 deserve special recognition for their enormous multi-year
2889 contributions!
2890
2892 Nmap Copyright and Licensing
2893 The Nmap Security Scanner is (C) 1996–2020 Insecure.Com LLC ("The Nmap
2894 Project"). Nmap is also a registered trademark of the Nmap Project. It
2895 is published under the Nmap Public Source License[18]. This generally
2896 allows end users to download and use Nmap for free. It doesn't not
2897 allow Nmap to be used and redistributed within commercial software or
2898 hardware products (including appliances, virtual machines, and
2899 traditional applications). We fund the project by selling a special
2900 Nmap OEM Edition for this purpose, as described at
2901 https://nmap.org/oem. Hundreds of large and small software vendors have
2902 already purchased OEM licenses to embed Nmap technology such as host
2903 discovery, port scanning, OS detection, version detection, and the Nmap
2904 Scripting Engine within their products.
2905 The Nmap Project has permission to redistribute Npcap, a packet
2907 capturing driver and library for the Microsoft Windows platform. Npcap
2908 is a separate work with it's own license rather than this Nmap license.
2909 Since the Npcap license does not permit redistribution without special
2910 permission, our Nmap Windows binary packages which contain Npcap may
2911 not be redistributed without special permission.
2912 Even though the NPSL is based on GPLv2, it contains different
2914 provisions and is not directly compatible. It is incompatible with some
2915 other open source licenses as well. In some cases we can relicense
2916 portions of Nmap or grant special permissions to use it in other open
2917 source software. Please contact fyodor@nmap.org with any such requests.
2918 Similarly, we don't incorporate incompatible open source software into
2919 Nmap without special permission from the copyright holders.
2920 If you have received a written license agreement or contract for Nmap
2922 stating terms other than these, you may choose to use and redistribute
2923 Nmap under those terms instead.
2924 Creative Commons License for this Nmap Guide
2926 This Nmap Reference Guide is (C) 2005–2020 Insecure.Com LLC. It is
2927 hereby placed under version 3.0 of the Creative Commons Attribution
2928 License[19]. This allows you redistribute and modify the work as you
2929 desire, as long as you credit the original source. Alternatively, you
2930 may choose to treat this document as falling under the same license as
2931 Nmap itself (discussed previously).
2932 Source Code Availability and Community Contributions
2934 Source is provided to this software because we believe users have a
2935 right to know exactly what a program is going to do before they run it.
2936 This also allows you to audit the software for security holes.
2937 Source code also allows you to port Nmap to new platforms, fix bugs,
2939 and add new features. You are highly encouraged to submit your changes
2940 as Github Pull Requests (PR) or send them to <dev@nmap.org> for
2941 possible incorporation into the main distribution. By submitting such
2942 changes, it is assumed that you are offering the Nmap Project the
2943 unlimited, non-exclusive right to reuse, modify, and relicense the
2944 code. This is important because the inability to relicense code has
2945 caused devastating problems for other Free Software projects (such as
2946 KDE and NASM). We also sell commercial licenses to Nmap OEM[20]. If you
2947 wish to specify special license conditions of your contributions, just
2948 say so when you send them.
2949 No Warranty
2951 This program is distributed in the hope that it will be useful, but
2952 WITHOUT ANY WARRANTY; without even the implied warranty of
2953 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
2954 It should also be noted that Nmap has occasionally been known to crash
2956 poorly written applications, TCP/IP stacks, and even operating systems.
2957 While this is extremely rare, it is important to keep in mind. Nmap
2958 should never be run against mission critical systems unless you are
2959 prepared to suffer downtime. We acknowledge here that Nmap may crash
2960 your systems or networks and we disclaim all liability for any damage
2961 or problems Nmap could cause.
2962 Inappropriate Usage
2964 Because of the slight risk of crashes and because a few black hats like
2965 to use Nmap for reconnaissance prior to attacking systems, there are
2966 administrators who become upset and may complain when their system is
2967 scanned. Thus, it is often advisable to request permission before doing
2968 even a light scan of a network.
2969 Nmap should never be installed with special privileges (e.g. suid
2971 root). That would open up a major security vulnerability as other
2972 users on the system (or attackers) could use it for privilege
2973 escalation.
2974 Nmap is not designed, manufactured, or intended for use in hazardous
2976 environments requiring fail- safe performance where the failure of the
2977 software could lead directly to death, personal injury, or significant
2978 physical or environmental damage.
2979 Third-Party Software and Funding Notices
2981 This product includes software developed by the Apache Software
2982 Foundation[21]. A modified version of the Libpcap portable packet
2983 capture library[22] is distributed along with Nmap. The Windows version
2984 of Nmap utilizes the Libpcap-derived Ncap library[23] instead. Regular
2985 expression support is provided by the PCRE library[24], which is
2986 open-source software, written by Philip Hazel. Certain raw networking
2987 functions use the Libdnet[25] networking library, which was written by
2988 Dug Song. A modified version is distributed with Nmap. Nmap can
2989 optionally link with the OpenSSL cryptography toolkit[26] for SSL
2990 version detection support. The Nmap Scripting Engine uses an embedded
2991 version of the Lua programming language[27]. The Liblinear linear
2992 classification library[28] is used for our IPv6 OS detection machine
2993 learning techniques[29].
2994 All of the third-party software described in this paragraph is freely
2996 redistributable under BSD-style software licenses.
2997 Binary packages for Windows and Mac OS X include support libraries
2999 necessary to run Zenmap and Ndiff with Python and PyGTK. (Unix
3000 platforms commonly make these libraries easy to install, so they are
3001 not part of the packages.) A listing of these support libraries and
3002 their licenses is included in the LICENSES files.
3003 This software was supported in part through the Google Summer of
3005 Code[30] and the DARPA CINDER program[31] (DARPA-BAA-10-84).
3006 United States Export Control
3008 Nmap only uses encryption when compiled with the optional OpenSSL
3009 support and linked with OpenSSL. When compiled without OpenSSL support,
3010 the Nmap Project believes that Nmap is not subject to U.S. Export
3011 Administration Regulations (EAR)[32] export control. As such, there is
3012 no applicable ECCN (export control classification number) and
3013 exportation does not require any special license, permit, or other
3014 governmental authorization.
3015 When compiled with OpenSSL support or distributed as source code, the
3017 Nmap Project believes that Nmap falls under U.S. ECCN 5D002[33]
3018 (“Information Security Software”). We distribute Nmap under the TSU
3019 exception for publicly available encryption software defined in EAR
3020 740.13(e)[34].
3021
3023 1. Nmap Network Scanning: The Official Nmap Project Guide to Network
3024 Discovery and Security Scanning
3025 https://nmap.org/book/
3026 2. RFC 1122
3028 http://www.rfc-editor.org/rfc/rfc1122.txt
3029 3. RFC 792
3031 http://www.rfc-editor.org/rfc/rfc792.txt
3032 4. RFC 950
3034 http://www.rfc-editor.org/rfc/rfc950.txt
3035 5. UDP
3037 http://www.rfc-editor.org/rfc/rfc768.txt
3038 6. SCTP
3040 http://www.rfc-editor.org/rfc/rfc4960.txt
3041 7. TCP RFC
3043 http://www.rfc-editor.org/rfc/rfc793.txt
3044 8. RFC 959
3046 http://www.rfc-editor.org/rfc/rfc959.txt
3047 9. RFC 1323
3049 http://www.rfc-editor.org/rfc/rfc1323.txt
3050 10. Lua programming language
3052 http://lua.org
3053 11. precedence
3055 http://www.lua.org/manual/5.1/manual.html#2.5.3
3056 12. IP protocol
3058 http://www.rfc-editor.org/rfc/rfc791.txt
3059 13. RFC 2960
3061 http://www.rfc-editor.org/rfc/rfc2960.txt
3062 14. Nmap::Scanner
3064 http://sourceforge.net/projects/nmap-scanner/
3065 15. Nmap::Parser
3067 http://nmapparser.wordpress.com/
3068 16. xsltproc
3070 http://xmlsoft.org/XSLT/
3071 17. listed at Wikipedia
3073 http://en.wikipedia.org/wiki/List_of_IPv6_tunnel_brokers
3074 18. Nmap Public Source License
3076 https://nmap.org/npsl
3077 19. Creative Commons Attribution License
3079 http://creativecommons.org/licenses/by/3.0/
3080 20. Nmap OEM
3082 https://nmap.org/oem
3083 21. Apache Software Foundation
3085 https://www.apache.org
3086 22. Libpcap portable packet capture library
3088 https://www.tcpdump.org
3089 23. Ncap library
3091 https://npcap.org
3092 24. PCRE library
3094 https://pcre.org
3095 25. Libdnet
3097 http://libdnet.sourceforge.net
3098 26. OpenSSL cryptography toolkit
3100 https://openssl.org
3101 27. Lua programming language
3103 https://lua.org
3104 28. Liblinear linear classification library
3106 https://www.csie.ntu.edu.tw/~cjlin/liblinear/
3107 29. IPv6 OS detection machine learning techniques
3109 https://nmap.org/book/osdetect-guess.html#osdetect-guess-ipv6
3110 30. Google Summer of Code
3112 https://nmap.org/soc/
3113 31. DARPA CINDER program
3115 https://www.fbo.gov/index?s=opportunity&mode=form&id=585e02a51f77af5cb3c9e06b9cc82c48&tab=core&_cview=1
3116 32. Export Administration Regulations (EAR)
3118 https://www.bis.doc.gov/index.php/regulations/export-administration-regulations-ear
3119 33. 5D002
3121 https://www.bis.doc.gov/index.php/documents/regulations-docs/federal-register-notices/federal-register-2014/951-ccl5-pt2/file
3122 34. EAR 740.13(e)
3124 https://www.bis.doc.gov/index.php/documents/regulations-docs/2341-740-2/file
3125Nmap 08/06/2021 NMAP(1)