1NCAT(1) Ncat Reference Guide NCAT(1)
2
6 ncat - Concatenate and redirect sockets
7
9 ncat [OPTIONS...] [hostname] [port]
10
12 Ncat is a feature-packed networking utility which reads and writes data
13 across networks from the command line. Ncat was written for the Nmap
14 Project and is the culmination of the currently splintered family of
15 Netcat incarnations. It is designed to be a reliable back-end tool to
16 instantly provide network connectivity to other applications and users.
17 Ncat will not only work with IPv4 and IPv6 but provides the user with a
18 virtually limitless number of potential uses.
19 Among Ncat's vast number of features there is the ability to chain
21 Ncats together; redirection of TCP, UDP, and SCTP ports to other sites;
22 SSL support; and proxy connections via SOCKS4 or HTTP proxies (with
23 optional proxy authentication as well). Some general principles apply
24 to most applications and thus give you the capability of instantly
25 adding networking support to software that would normally never support
26 it.
27
29 Ncat 7.50 ( https://nmap.org/ncat )
30 Usage: ncat [options] [hostname] [port]
31 Options taking a time assume seconds. Append 'ms' for milliseconds,
33 's' for seconds, 'm' for minutes, or 'h' for hours (e.g. 500ms).
34 -4 Use IPv4 only
35 -6 Use IPv6 only
36 -U, --unixsock Use Unix domain sockets only
37 -C, --crlf Use CRLF for EOL sequence
38 -c, --sh-exec <command> Executes the given command via /bin/sh
39 -e, --exec <command> Executes the given command
40 --lua-exec <filename> Executes the given Lua script
41 -g hop1[,hop2,...] Loose source routing hop points (8 max)
42 -G <n> Loose source routing hop pointer (4, 8, 12, ...)
43 -m, --max-conns <n> Maximum <n> simultaneous connections
44 -h, --help Display this help screen
45 -d, --delay <time> Wait between read/writes
46 -o, --output <filename> Dump session data to a file
47 -x, --hex-dump <filename> Dump session data as hex to a file
48 -i, --idle-timeout <time> Idle read/write timeout
49 -p, --source-port port Specify source port to use
50 -s, --source addr Specify source address to use (doesn't affect -l)
51 -l, --listen Bind and listen for incoming connections
52 -k, --keep-open Accept multiple connections in listen mode
53 -n, --nodns Do not resolve hostnames via DNS
54 -t, --telnet Answer Telnet negotiations
55 -u, --udp Use UDP instead of default TCP
56 --sctp Use SCTP instead of default TCP
57 -v, --verbose Set verbosity level (can be used several times)
58 -w, --wait <time> Connect timeout
59 -z Zero-I/O mode, report connection status only
60 --append-output Append rather than clobber specified output files
61 --send-only Only send data, ignoring received; quit on EOF
62 --recv-only Only receive data, never send anything
63 --allow Allow only given hosts to connect to Ncat
64 --allowfile A file of hosts allowed to connect to Ncat
65 --deny Deny given hosts from connecting to Ncat
66 --denyfile A file of hosts denied from connecting to Ncat
67 --broker Enable Ncat's connection brokering mode
68 --chat Start a simple Ncat chat server
69 --proxy <addr[:port]> Specify address of host to proxy through
70 --proxy-type <type> Specify proxy type ("http" or "socks4" or "socks5")
71 --proxy-auth <auth> Authenticate with HTTP or SOCKS proxy server
72 --ssl Connect or listen with SSL
73 --ssl-cert Specify SSL certificate file (PEM) for listening
74 --ssl-key Specify SSL private key (PEM) for listening
75 --ssl-verify Verify trust and domain name of certificates
76 --ssl-trustfile PEM file containing trusted SSL certificates
77 --ssl-ciphers Cipherlist containing SSL ciphers to use
78 --version Display Ncat's version information and exit
79 See the ncat(1) manpage for full options, descriptions and usage examples
81
84 Ncat operates in one of two primary modes: connect mode and listen
85 mode. Other modes, such as the HTTP proxy server, act as special cases
86 of these two. In connect mode, Ncat works as a client. In listen mode
87 it is a server.
88 In connect mode, the hostname and port arguments tell what to connect
90 to. hostname is required, and may be a hostname or IP address. If port
91 is supplied, it must be a decimal port number. If omitted, it defaults
92 to 31337.
93 In listen mode, hostname and port control the address the server will
95 bind to. Both arguments are optional in listen mode. If hostname is
96 omitted, it defaults to listening on all available addresses over IPv4
97 and IPv6. If port is omitted, it defaults to 31337.
98
100 -4 (IPv4 only)
101 Force the use of IPv4 only.
102 -6 (IPv6 only)
104 Force the use of IPv6 only.
105 -U, --unixsock (Use Unix domain sockets)
107 Use Unix domain sockets rather than network sockets. This option
108 may be used on its own for stream sockets, or combined with --udp
109 for datagram sockets. A description of -U mode is in the section
110 called “UNIX DOMAIN SOCKETS”.
111 -u, --udp (Use UDP)
113 Use UDP for the connection (the default is TCP).
114 --sctp (Use SCTP)
116 Use SCTP for the connection (the default is TCP). SCTP support is
117 implemented in TCP-compatible mode.
118
120 -g hop1[,hop2,...] (Loose source routing)
121 Sets hops for IPv4 loose source routing. You can use -g once with a
122 comma-separated list of hops, use -g multiple times with single
123 hops to build the list, or combine the two. Hops can be given as IP
124 addresses or hostnames.
125 -G ptr (Set source routing pointer)
127 Sets the IPv4 source route “pointer” for use with -g. The argument
128 must be a multiple of 4 and no more than 28. Not all operating
129 systems support setting this pointer to anything other than four.
130 -p port, --source-port port (Specify source port)
132 Set the port number for Ncat to bind to.
133 -s host, --source host (Specify source address)
135 Set the address for Ncat to bind to.
136
138 See the section called “ACCESS CONTROL OPTIONS” for information on
139 limiting the hosts that may connect to the listening Ncat process.
140 -l, --listen (Listen for connections)
142 Listen for connections rather than connecting to a remote machine
143 -m numconns, --max-conns numconns (Specify maximum number of
145 connections)
146 The maximum number of simultaneous connections accepted by an Ncat
147 instance. 100 is the default (60 on Windows).
148 -k, --keep-open (Accept multiple connections)
150 Normally a listening server accepts only one connection and then
151 quits when the connection is closed. This option makes it accept
152 multiple simultaneous connections and wait for more connections
153 after they have all been closed. It must be combined with --listen.
154 In this mode there is no way for Ncat to know when its network
155 input is finished, so it will keep running until interrupted. This
156 also means that it will never close its output stream, so any
157 program reading from Ncat and looking for end-of-file will also
158 hang.
159 --broker (Connection brokering)
161 Allow multiple parties to connect to a centralised Ncat server and
162 communicate with each other. Ncat can broker communication between
163 systems that are behind a NAT or otherwise unable to directly
164 connect. This option is used in conjunction with --listen, which
165 causes the --listen port to have broker mode enabled.
166 --chat (Ad-hoc “chat server”)
168 The --chat option enables chat mode, intended for the exchange of
169 text between several users. In chat mode, connection brokering is
170 turned on. Ncat prefixes each message received with an ID before
171 relaying it to the other connections. The ID is unique for each
172 connected client. This helps distinguish who sent what.
173 Additionally, non-printing characters such as control characters
174 are escaped to keep them from doing damage to a terminal.
175
177 --ssl (Use SSL)
178 In connect mode, this option transparently negotiates an SSL
179 session with an SSL server to securely encrypt the connection. This
180 is particularly handy for talking to SSL enabled HTTP servers, etc.
181 In server mode, this option listens for incoming SSL connections,
183 rather than plain untunneled traffic.
184 --ssl-verify (Verify server certificates)
186 In client mode, --ssl-verify is like --ssl except that it also
187 requires verification of the server certificate. Ncat comes with a
188 default set of trusted certificates in the file ca-bundle.crt.
189 Some operating systems provide a default list of trusted
190 certificates; these will also be used if available. Use
191 --ssl-trustfile to give a custom list. Use -v one or more times to
192 get details about verification failures. Ncat does not check for
193 revoked certificates.
194 This option has no effect in server mode.
196 --ssl-cert certfile.pem (Specify SSL certificate)
198 This option gives the location of a PEM-encoded certificate files
199 used to authenticate the server (in listen mode) or the client (in
200 connect mode). Use it in combination with --ssl-key.
201 --ssl-key keyfile.pem (Specify SSL private key)
203 This option gives the location of the PEM-encoded private key file
204 that goes with the certificate named with --ssl-cert.
205 --ssl-trustfile cert.pem (List trusted certificates)
207 This option sets a list of certificates that are trusted for
208 purposes of certificate verification. It has no effect unless
209 combined with --ssl-verify. The argument to this option is the name
210 of a PEM file containing trusted certificates. Typically, the file
211 will contain certificates of certification authorities, though it
212 may also contain server certificates directly. When this option is
213 used, Ncat does not use its default certificates.
214 --ssl-ciphers cipherlist (Specify SSL ciphersuites)
216 This option sets the list of ciphersuites that Ncat will use when
217 connecting to servers or when accepting SSL connections from
218 clients. The syntax is described in the OpenSSL ciphers(1) man
219 page, and defaults to ALL:!ADH:!LOW:!EXP:!MD5:@STRENGTH
220
222 --proxy host[:port] (Specify proxy address)
223 Requests proxying through host:port, using the protocol specified
224 by --proxy-type.
225 If no port is specified, the proxy protocol's well-known port is
227 used (1080 for SOCKS and 3128 for HTTP). However, when specifying
228 an IPv6 HTTP proxy server using the IP address rather than the
229 hostname, the port number MUST be specified as well. If the proxy
230 requires authentication, use --proxy-auth.
231 --proxy-type proto (Specify proxy protocol)
233 In connect mode, this option requests the protocol proto to connect
234 through the proxy host specified by --proxy. In listen mode, this
235 option has Ncat act as a proxy server using the specified protocol.
236 The currently available protocols in connect mode are http
238 (CONNECT) and socks4 (SOCKSv4). The only server currently supported
239 is http. If this option is not used, the default protocol is http.
240 --proxy-auth user[:pass] (Specify proxy credentials)
242 In connect mode, gives the credentials that will be used to connect
243 to the proxy server. In listen mode, gives the credentials that
244 will be required of connecting clients. For use with --proxy-type
245 http, the form should be user:pass. For --proxy-type socks4, it
246 should be a username only.
247
249 -e command, --exec command (Execute command)
250 Execute the specified command after a connection has been
251 established. The command must be specified as a full pathname. All
252 input from the remote client will be sent to the application and
253 responses sent back to the remote client over the socket, thus
254 making your command-line application interactive over a socket.
255 Combined with --keep-open, Ncat will handle multiple simultaneous
256 connections to your specified port/application like inetd. Ncat
257 will only accept a maximum, definable, number of simultaneous
258 connections controlled by the -m option. By default this is set to
259 100 (60 on Windows).
260 -c command, --sh-exec command (Execute command via sh)
262 Same as -e, except it tries to execute the command via /bin/sh.
263 This means you don't have to specify the full path for the command,
264 and shell facilities like environment variables are available.
265 --lua-exec file (Execute a .lua script)
267 Runs the specified file as a Lua script after a connection has been
268 established, using a built-in interpreter. Both the script's
269 standard input and the standard output are redirected to the
270 connection data streams.
271 All exec options add the following variables to the child's
273 environment:
274 NCAT_REMOTE_ADDR, NCAT_REMOTE_PORT
276 The IP address and port number of the remote host. In connect mode,
277 it's the target's address; in listen mode, it's the client's
278 address.
279 NCAT_LOCAL_ADDR, NCAT_LOCAL_PORT
281 The IP address and port number of the local end of the connection.
282 NCAT_PROTO
284 The protocol in use: one of TCP, UDP, and SCTP.
285
287 --allow host[,host,...] (Allow connections)
288 The list of hosts specified will be the only hosts allowed to
289 connect to the Ncat process. All other connection attempts will be
290 disconnected. In case of a conflict between --allow and --deny,
291 --allow takes precedence. Host specifications follow the same
292 syntax used by Nmap.
293 --allowfile file (Allow connections from file)
295 This has the same functionality as --allow, except that the allowed
296 hosts are provided in a new-line delimited allow file, rather than
297 directly on the command line.
298 --deny host[,host,...] (Deny connections)
300 Issue Ncat with a list of hosts that will not be allowed to connect
301 to the listening Ncat process. Specified hosts will have their
302 session silently terminated if they try to connect. In case of a
303 conflict between --allow and --deny, --allow takes precedence. Host
304 specifications follow the same syntax used by Nmap.
305 --denyfile file (Deny connections from file)
307 This is the same functionality as --deny, except that excluded
308 hosts are provided in a new-line delimited deny file, rather than
309 directly on the command line.
310
312 These options accept a time parameter. This is specified in seconds by
313 default, though you can append ms, s, m, or h to the value to specify
314 milliseconds, seconds, minutes, or hours.
315 -d time, --delay time (Specify line delay)
317 Set the delay interval for lines sent. This effectively limits the
318 number of lines that Ncat will send in the specified period. This
319 may be useful for low-bandwidth sites, or have other uses such as
320 coping with annoying iptables --limit options.
321 -i time, --idle-timeout time (Specify idle timeout)
323 Set a fixed timeout for idle connections. If the idle timeout is
324 reached, the connection is terminated.
325 -w time, --wait time (Specify connect timeout)
327 Set a fixed timeout for connection attempts.
328
330 -o file, --output file (Save session data)
331 Dump session data to a file
332 -x file, --hex-dump file (Save session data in hex)
334 Dump session data in hex to a file.
335 --append-output (Append output)
337 Issue Ncat with --append-ouput along with -o and/or -x and it will
338 append the resulted output rather than truncating the specified
339 output files.
340 -v, --verbose (Be verbose)
342 Issue Ncat with -v and it will be verbose and display all kinds of
343 useful connection based information. Use more than once (-vv,
344 -vvv...) for greater verbosity.
345
347 -C, --crlf (Use CRLF as EOL)
348 This option tells Ncat to convert LF line endings to CRLF when
349 taking input from standard input. This is useful for talking to
350 some stringent servers directly from a terminal in one of the many
351 common plain-text protocols that use CRLF for end-of-line.
352 -h, --help (Help screen)
354 Displays a short help screen with common options and parameters,
355 and then exits.
356 --recv-only (Only receive data)
358 If this option is passed, Ncat will only receive data and will not
359 try to send anything.
360 --send-only (Only send data)
362 If this option is passed, then Ncat will only send data and will
363 ignore anything received. This option also causes Ncat to close the
364 network connection and terminate after EOF is received on standard
365 input.
366 --no-shutdown (Do not shutdown into half-duplex mode)
368 If this option is passed, Ncat will not invoke shutdown on a socket
369 aftering seeing EOF on stdin. This is provided for
370 backward-compatibility with OpenBSD netcat, which exhibits this
371 behavior when executed with its '-d' option.
372 -t, --telnet (Answer Telnet negotiations)
374 Handle DO/DONT WILL/WONT Telnet negotiations. This makes it
375 possible to script Telnet sessions with Ncat.
376 --version (Display version)
378 Displays the Ncat version number and exits.
379
381 The -U option (same as --unixsock) causes Ncat to use Unix domain
382 sockets rather than network sockets. Unix domain sockets exist as an
383 entry in the filesystem. You must give the name of a socket to connect
384 to or to listen on. For example, to make a connection,
385 ncat -U ~/unixsock
387 To listen on a socket:
389 ncat -l -U ~/unixsock
391 Listen mode will create the socket if it doesn't exist. The socket will
393 continue to exist after the program ends.
394 Both stream and datagram domain sockets are supported. Use -U on its
396 own for stream sockets, or combine it with --udp for datagram sockets.
397 Datagram sockets require a source socket to connect from. By default, a
398 source socket with a random filename will be created as needed, and
399 deleted when the program ends. Use the --source with a path to use a
400 source socket with a specific name.
401
403 Connect to example.org on TCP port 8080.
404 ncat example.org 8080
405 Listen for connections on TCP port 8080.
407 ncat -l 8080
408 Redirect TCP port 8080 on the local machine to host on port 80.
410 ncat --sh-exec "ncat example.org 80" -l 8080 --keep-open
411 Bind to TCP port 8081 and attach /bin/bash for the world to access
413 freely.
414 ncat --exec "/bin/bash" -l 8081 --keep-open
415 Bind a shell to TCP port 8081, limit access to hosts on a local
417 network, and limit the maximum number of simultaneous connections to 3.
418 ncat --exec "/bin/bash" --max-conns 3 --allow 192.168.0.0/24 -l
419 8081 --keep-open
420 Connect to smtphost:25 through a SOCKS4 server on port 1080.
422 ncat --proxy socks4host --proxy-type socks4 --proxy-auth user
423 smtphost 25
424 Create an HTTP proxy server on localhost port 8888.
426 ncat -l --proxy-type http localhost 8888
427 Send a file over TCP port 9899 from host2 (client) to host1 (server).
429 HOST1$ ncat -l 9899 > outputfile
430 HOST2$ ncat HOST1 9899 < inputfile
432 Transfer in the other direction, turning Ncat into a “one file” server.
434 HOST1$ ncat -l 9899 < inputfile
435 HOST2$ ncat HOST1 9899 > outputfile
437
439 The exit code reflects whether a connection was made and completed
440 successfully. 0 means there was no error. 1 means there was a network
441 error of some kind, for example “Connection refused” or “Connection
442 reset”. 2 is reserved for all other errors, like an invalid option or a
443 nonexistent file.
444
446 Like its authors, Ncat isn't perfect. But you can help make it better
447 by sending bug reports or even writing patches. If Ncat doesn't behave
448 the way you expect, first upgrade to the latest version available from
449 https://nmap.org. If the problem persists, do some research to
450 determine whether it has already been discovered and addressed. Try
451 Googling the error message or browsing the nmap-dev archives at
452 http://seclists.org/. Read this full manual page as well. If nothing
453 comes of this, mail a bug report to <dev@nmap.org>. Please include
454 everything you have learned about the problem, as well as what version
455 of Ncat you are running and what operating system version it is running
456 on. Problem reports and Ncat usage questions sent to dev@nmap.org are
457 far more likely to be answered than those sent to Fyodor directly.
458 Code patches to fix bugs are even better than bug reports. Basic
460 instructions for creating patch files with your changes are available
461 at https://svn.nmap.org/nmap/HACKING. Patches may be sent to nmap-dev
462 (recommended) or to Fyodor directly.
463
465 · Chris Gibson <chris@linuxops.net>
466 · Kris Katterjohn <katterjohn@gmail.com>
468 · Mixter <mixter@gmail.com>
470 · Fyodor <fyodor@nmap.org> (http://insecure.org)
472 The original Netcat was written by *Hobbit* <hobbit@avian.org>. While
474 Ncat isn't built on any code from the “traditional” Netcat (or any
475 other implementation), Ncat is most definitely based on Netcat in
476 spirit and functionality.
477
479 Ncat Copyright and Licensing
480 Ncat is (C) 2005–2012 Insecure.Com LLC. It is distributed as free and
481 open source software under the same license terms as our Nmap software.
482 Precise terms and further details are available from
483 https://nmap.org/man/man-legal.html.
484 Creative Commons License for this Ncat Guide
486 This Ncat Reference Guide is (C) 2005–2012 Insecure.Com LLC. It is
487 hereby placed under version 3.0 of the Creative Commons Attribution
488 License[1]. This allows you redistribute and modify the work as you
489 desire, as long as you credit the original source. Alternatively, you
490 may choose to treat this document as falling under the same license as
491 Ncap itself (discussed previously).
492 Source Code Availability and Community Contributions
494 Source is provided to this software because we believe users have a
495 right to know exactly what a program is going to do before they run it.
496 This also allows you to audit the software for security holes (none
497 have been found so far).
498 Source code also allows you to port Nmap (which includes Ncat) to new
500 platforms, fix bugs, and add new features. You are highly encouraged to
501 send your changes to <dev@nmap.org> for possible incorporation into the
502 main distribution. By sending these changes to Fyodor or one of the
503 Insecure.Org development mailing lists, it is assumed that you are
504 offering the Nmap Project (Insecure.Com LLC) the unlimited,
505 non-exclusive right to reuse, modify, and relicense the code. Nmap will
506 always be available open source, but this is important because the
507 inability to relicense code has caused devastating problems for other
508 Free Software projects (such as KDE and NASM). We also occasionally
509 relicense the code to third parties as discussed in the Nmap man page.
510 If you wish to specify special license conditions of your
511 contributions, just say so when you send them.
512 No Warranty
514 This program is distributed in the hope that it will be useful, but
515 WITHOUT ANY WARRANTY; without even the implied warranty of
516 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
517 General Public License v2.0 for more details at
518 http://www.gnu.org/licenses/gpl-2.0.html, or in the COPYING file
519 included with Nmap.
520 Inappropriate Usage
522 Ncat should never be installed with special privileges (e.g. suid
523 root). That would open up a major security vulnerability as other
524 users on the system (or attackers) could use it for privilege
525 escalation.
526 Third-Party Software
528 This product includes software developed by the Apache Software
529 Foundation[2]. A modified version of the Libpcap portable packet
530 capture library[3] is distributed along with Ncat. The Windows version
531 of Ncat utilized the Libpcap-derived WinPcap library[4] instead.
532 Certain raw networking functions use the Libdnet[5] networking library,
533 which was written by Dug Song. A modified version is distributed with
534 Ncat. Ncat can optionally link with the OpenSSL cryptography toolkit[6]
535 for SSL version detection support. All of the third-party software
536 described in this paragraph is freely redistributable under BSD-style
537 software licenses.
538
540 1. Creative Commons Attribution License
541 http://creativecommons.org/licenses/by/3.0/
542 2. Apache Software Foundation
544 http://www.apache.org
545 3. Libpcap portable packet capture library
547 http://www.tcpdump.org
548 4. WinPcap library
550 http://www.winpcap.org
551 5. Libdnet
553 http://libdnet.sourceforge.net
554 6. OpenSSL cryptography toolkit
556 http://www.openssl.org
557Ncat 06/07/2017 NCAT(1)