1NCAT(1)                      Ncat Reference Guide                      NCAT(1)
2
3
4

NAME

6       ncat - Concatenate and redirect sockets
7

SYNOPSIS

9       ncat [OPTIONS...] [hostname] [port]
10

DESCRIPTION

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
20       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, SOCKS5 or HTTP proxies
23       (with optional proxy authentication as well). Some general principles
24       apply to most applications and thus give you the capability of
25       instantly adding networking support to software that would normally
26       never support it.
27

OPTIONS SUMMARY

29           Ncat 7.70 ( https://nmap.org/ncat )
30           Usage: ncat [options] [hostname] [port]
31
32           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                 --ssl-alpn             ALPN protocol list to use.
79                 --version              Display Ncat's version information and exit
80
81           See the ncat(1) manpage for full options, descriptions and usage examples
82
83

CONNECT MODE AND LISTEN MODE

85       Ncat operates in one of two primary modes: connect mode and listen
86       mode. Other modes, such as the HTTP proxy server, act as special cases
87       of these two. In connect mode, Ncat works as a client. In listen mode
88       it is a server.
89
90       In connect mode, the hostname and port arguments tell what to connect
91       to.  hostname is required, and may be a hostname or IP address. If port
92       is supplied, it must be a decimal port number. If omitted, it defaults
93       to 31337.
94
95       In listen mode, hostname and port control the address the server will
96       bind to. Both arguments are optional in listen mode. If hostname is
97       omitted, it defaults to listening on all available addresses over IPv4
98       and IPv6. If port is omitted, it defaults to 31337.
99

PROTOCOL OPTIONS

101       -4 (IPv4 only)
102           Force the use of IPv4 only.
103
104       -6 (IPv6 only)
105           Force the use of IPv6 only.
106
107       -U, --unixsock (Use Unix domain sockets)
108           Use Unix domain sockets rather than network sockets. This option
109           may be used on its own for stream sockets, or combined with --udp
110           for datagram sockets. A description of -U mode is in the section
111           called “UNIX DOMAIN SOCKETS”.
112
113       -u, --udp (Use UDP)
114           Use UDP for the connection (the default is TCP).
115
116       --sctp (Use SCTP)
117           Use SCTP for the connection (the default is TCP). SCTP support is
118           implemented in TCP-compatible mode.
119

CONNECT MODE OPTIONS

121       -g hop1[,hop2,...] (Loose source routing)
122           Sets hops for IPv4 loose source routing. You can use -g once with a
123           comma-separated list of hops, use -g multiple times with single
124           hops to build the list, or combine the two. Hops can be given as IP
125           addresses or hostnames.
126
127       -G ptr (Set source routing pointer)
128           Sets the IPv4 source route “pointer” for use with -g. The argument
129           must be a multiple of 4 and no more than 28. Not all operating
130           systems support setting this pointer to anything other than four.
131
132       -p port, --source-port port (Specify source port)
133           Set the port number for Ncat to bind to.
134
135       -s host, --source host (Specify source address)
136           Set the address for Ncat to bind to.
137

LISTEN MODE OPTIONS

139       See the section called “ACCESS CONTROL OPTIONS” for information on
140       limiting the hosts that may connect to the listening Ncat process.
141
142       -l, --listen (Listen for connections)
143           Listen for connections rather than connecting to a remote machine
144
145       -m numconns, --max-conns numconns (Specify maximum number of
146       connections)
147           The maximum number of simultaneous connections accepted by an Ncat
148           instance. 100 is the default (60 on Windows).
149
150       -k, --keep-open (Accept multiple connections)
151           Normally a listening server accepts only one connection and then
152           quits when the connection is closed. This option makes it accept
153           multiple simultaneous connections and wait for more connections
154           after they have all been closed. It must be combined with --listen.
155           In this mode there is no way for Ncat to know when its network
156           input is finished, so it will keep running until interrupted. This
157           also means that it will never close its output stream, so any
158           program reading from Ncat and looking for end-of-file will also
159           hang.
160
161       --broker (Connection brokering)
162           Allow multiple parties to connect to a centralised Ncat server and
163           communicate with each other. Ncat can broker communication between
164           systems that are behind a NAT or otherwise unable to directly
165           connect. This option is used in conjunction with --listen, which
166           causes the --listen port to have broker mode enabled.
167
168       --chat (Ad-hoc “chat server”)
169           The --chat option enables chat mode, intended for the exchange of
170           text between several users. In chat mode, connection brokering is
171           turned on. Ncat prefixes each message received with an ID before
172           relaying it to the other connections. The ID is unique for each
173           connected client. This helps distinguish who sent what.
174           Additionally, non-printing characters such as control characters
175           are escaped to keep them from doing damage to a terminal.
176

SSL OPTIONS

178       --ssl (Use SSL)
179           In connect mode, this option transparently negotiates an SSL
180           session with an SSL server to securely encrypt the connection. This
181           is particularly handy for talking to SSL enabled HTTP servers, etc.
182
183           In server mode, this option listens for incoming SSL connections,
184           rather than plain untunneled traffic.
185
186           In UDP connect mode, this option enables Datagram TLS (DTLS). This
187           is not supported in server mode.
188
189       --ssl-verify (Verify server certificates)
190           In client mode, --ssl-verify is like --ssl except that it also
191           requires verification of the server certificate. Ncat comes with a
192           default set of trusted certificates in the file ca-bundle.crt.
193           Some operating systems provide a default list of trusted
194           certificates; these will also be used if available. Use
195           --ssl-trustfile to give a custom list. Use -v one or more times to
196           get details about verification failures.  Ncat does not check for
197           revoked certificates.
198
199           This option has no effect in server mode.
200
201       --ssl-cert certfile.pem (Specify SSL certificate)
202           This option gives the location of a PEM-encoded certificate files
203           used to authenticate the server (in listen mode) or the client (in
204           connect mode). Use it in combination with --ssl-key.
205
206       --ssl-key keyfile.pem (Specify SSL private key)
207           This option gives the location of the PEM-encoded private key file
208           that goes with the certificate named with --ssl-cert.
209
210       --ssl-trustfile cert.pem (List trusted certificates)
211           This option sets a list of certificates that are trusted for
212           purposes of certificate verification. It has no effect unless
213           combined with --ssl-verify. The argument to this option is the name
214           of a PEM file containing trusted certificates. Typically, the file
215           will contain certificates of certification authorities, though it
216           may also contain server certificates directly. When this option is
217           used, Ncat does not use its default certificates.
218
219       --ssl-ciphers cipherlist (Specify SSL ciphersuites)
220           This option sets the list of ciphersuites that Ncat will use when
221           connecting to servers or when accepting SSL connections from
222           clients. The syntax is described in the OpenSSL ciphers(1) man
223           page, and defaults to
224           ALL:!aNULL:!eNULL:!LOW:!EXP:!RC4:!MD5:@STRENGTH
225
226       --ssl-alpn ALPN list (Specify ALPN protocol list)
227           This option allows you to specify a comma-separated list of
228           protocols to send via the Application-Layer Protocol Negotiation
229           (ALPN) TLS extension. Not supported by all versions of OpenSSL.
230

PROXY OPTIONS

232       --proxy host[:port] (Specify proxy address)
233           Requests proxying through host:port, using the protocol specified
234           by --proxy-type.
235
236           If no port is specified, the proxy protocol's well-known port is
237           used (1080 for SOCKS and 3128 for HTTP). However, when specifying
238           an IPv6 HTTP proxy server using the IP address rather than the
239           hostname, the port number MUST be specified as well. If the proxy
240           requires authentication, use --proxy-auth.
241
242       --proxy-type proto (Specify proxy protocol)
243           In connect mode, this option requests the protocol proto to connect
244           through the proxy host specified by --proxy. In listen mode, this
245           option has Ncat act as a proxy server using the specified protocol.
246
247           The currently available protocols in connect mode are http
248           (CONNECT), socks4 (SOCKSv4), and socks5 (SOCKSv5). The only server
249           currently supported is http. If this option is not used, the
250           default protocol is http.
251
252       --proxy-auth user[:pass] (Specify proxy credentials)
253           In connect mode, gives the credentials that will be used to connect
254           to the proxy server. In listen mode, gives the credentials that
255           will be required of connecting clients. For use with --proxy-type
256           http or --proxy-type socks5, the form should be username:password.
257           For --proxy-type socks4, it should be a username only.
258

COMMAND EXECUTION OPTIONS

260       -e command, --exec command (Execute command)
261           Execute the specified command after a connection has been
262           established. The command must be specified as a full pathname. All
263           input from the remote client will be sent to the application and
264           responses sent back to the remote client over the socket, thus
265           making your command-line application interactive over a socket.
266           Combined with --keep-open, Ncat will handle multiple simultaneous
267           connections to your specified port/application like inetd. Ncat
268           will only accept a maximum, definable, number of simultaneous
269           connections controlled by the -m option. By default this is set to
270           100 (60 on Windows).
271
272       -c command, --sh-exec command (Execute command via sh)
273           Same as -e, except it tries to execute the command via /bin/sh.
274           This means you don't have to specify the full path for the command,
275           and shell facilities like environment variables are available.
276
277       --lua-exec file (Execute a .lua script)
278           Runs the specified file as a Lua script after a connection has been
279           established, using a built-in interpreter. Both the script's
280           standard input and the standard output are redirected to the
281           connection data streams.
282
283       All exec options add the following variables to the child's
284       environment:
285
286       NCAT_REMOTE_ADDR, NCAT_REMOTE_PORT
287           The IP address and port number of the remote host. In connect mode,
288           it's the target's address; in listen mode, it's the client's
289           address.
290
291       NCAT_LOCAL_ADDR, NCAT_LOCAL_PORT
292           The IP address and port number of the local end of the connection.
293
294       NCAT_PROTO
295           The protocol in use: one of TCP, UDP, and SCTP.
296

ACCESS CONTROL OPTIONS

298       --allow host[,host,...] (Allow connections)
299           The list of hosts specified will be the only hosts allowed to
300           connect to the Ncat process. All other connection attempts will be
301           disconnected. In case of a conflict between --allow and --deny,
302           --allow takes precedence. Host specifications follow the same
303           syntax used by Nmap.
304
305       --allowfile file (Allow connections from file)
306           This has the same functionality as --allow, except that the allowed
307           hosts are provided in a new-line delimited allow file, rather than
308           directly on the command line.
309
310       --deny host[,host,...] (Deny connections)
311           Issue Ncat with a list of hosts that will not be allowed to connect
312           to the listening Ncat process. Specified hosts will have their
313           session silently terminated if they try to connect. In case of a
314           conflict between --allow and --deny, --allow takes precedence. Host
315           specifications follow the same syntax used by Nmap.
316
317       --denyfile file (Deny connections from file)
318           This is the same functionality as --deny, except that excluded
319           hosts are provided in a new-line delimited deny file, rather than
320           directly on the command line.
321

TIMING OPTIONS

323       These options accept a time parameter. This is specified in seconds by
324       default, though you can append ms, s, m, or h to the value to specify
325       milliseconds, seconds, minutes, or hours.
326
327       -d time, --delay time (Specify line delay)
328           Set the delay interval for lines sent. This effectively limits the
329           number of lines that Ncat will send in the specified period. This
330           may be useful for low-bandwidth sites, or have other uses such as
331           coping with annoying iptables --limit options.
332
333       -i time, --idle-timeout time (Specify idle timeout)
334           Set a fixed timeout for idle connections. If the idle timeout is
335           reached, the connection is terminated.
336
337       -w time, --wait time (Specify connect timeout)
338           Set a fixed timeout for connection attempts.
339

OUTPUT OPTIONS

341       -o file, --output file (Save session data)
342           Dump session data to a file
343
344       -x file, --hex-dump file (Save session data in hex)
345           Dump session data in hex to a file.
346
347       --append-output (Append output)
348           Issue Ncat with --append-ouput along with -o and/or -x and it will
349           append the resulted output rather than truncating the specified
350           output files.
351
352       -v, --verbose (Be verbose)
353           Issue Ncat with -v and it will be verbose and display all kinds of
354           useful connection based information. Use more than once (-vv,
355           -vvv...) for greater verbosity.
356

MISC OPTIONS

358       -C, --crlf (Use CRLF as EOL)
359           This option tells Ncat to convert LF line endings to CRLF when
360           taking input from standard input.  This is useful for talking to
361           some stringent servers directly from a terminal in one of the many
362           common plain-text protocols that use CRLF for end-of-line.
363
364       -h, --help (Help screen)
365           Displays a short help screen with common options and parameters,
366           and then exits.
367
368       --recv-only (Only receive data)
369           If this option is passed, Ncat will only receive data and will not
370           try to send anything.
371
372       --send-only (Only send data)
373           If this option is passed, then Ncat will only send data and will
374           ignore anything received. This option also causes Ncat to close the
375           network connection and terminate after EOF is received on standard
376           input.
377
378       --no-shutdown (Do not shutdown into half-duplex mode)
379           If this option is passed, Ncat will not invoke shutdown on a socket
380           aftering seeing EOF on stdin. This is provided for
381           backward-compatibility with OpenBSD netcat, which exhibits this
382           behavior when executed with its '-d' option.
383
384       -t, --telnet (Answer Telnet negotiations)
385           Handle DO/DONT WILL/WONT Telnet negotiations. This makes it
386           possible to script Telnet sessions with Ncat.
387
388       --version (Display version)
389           Displays the Ncat version number and exits.
390

UNIX DOMAIN SOCKETS

392       The -U option (same as --unixsock) causes Ncat to use Unix domain
393       sockets rather than network sockets. Unix domain sockets exist as an
394       entry in the filesystem. You must give the name of a socket to connect
395       to or to listen on. For example, to make a connection,
396
397       ncat -U ~/unixsock
398
399       To listen on a socket:
400
401       ncat -l -U ~/unixsock
402
403       Listen mode will create the socket if it doesn't exist. The socket will
404       continue to exist after the program ends.
405
406       Both stream and datagram domain sockets are supported. Use -U on its
407       own for stream sockets, or combine it with --udp for datagram sockets.
408       Datagram sockets require a source socket to connect from. By default, a
409       source socket with a random filename will be created as needed, and
410       deleted when the program ends. Use the --source with a path to use a
411       source socket with a specific name.
412

EXAMPLES

414       Connect to example.org on TCP port 8080.
415           ncat example.org 8080
416
417       Listen for connections on TCP port 8080.
418           ncat -l 8080
419
420       Redirect TCP port 8080 on the local machine to host on port 80.
421           ncat --sh-exec "ncat example.org 80" -l 8080 --keep-open
422
423       Bind to TCP port 8081 and attach /bin/bash for the world to access
424       freely.
425           ncat --exec "/bin/bash" -l 8081 --keep-open
426
427       Bind a shell to TCP port 8081, limit access to hosts on a local
428       network, and limit the maximum number of simultaneous connections to 3.
429           ncat --exec "/bin/bash" --max-conns 3 --allow 192.168.0.0/24 -l
430           8081 --keep-open
431
432       Connect to smtphost:25 through a SOCKS4 server on port 1080.
433           ncat --proxy socks4host --proxy-type socks4 --proxy-auth joe
434           smtphost 25
435
436       Connect to smtphost:25 through a SOCKS5 server on port 1080.
437           ncat --proxy socks5host --proxy-type socks5 --proxy-auth joe:secret
438           smtphost 25
439
440       Create an HTTP proxy server on localhost port 8888.
441           ncat -l --proxy-type http localhost 8888
442
443       Send a file over TCP port 9899 from host2 (client) to host1 (server).
444           HOST1$ ncat -l 9899 > outputfile
445
446           HOST2$ ncat HOST1 9899 < inputfile
447
448       Transfer in the other direction, turning Ncat into a “one file” server.
449           HOST1$ ncat -l 9899 < inputfile
450
451           HOST2$ ncat HOST1 9899 > outputfile
452

EXIT CODE

454       The exit code reflects whether a connection was made and completed
455       successfully. 0 means there was no error. 1 means there was a network
456       error of some kind, for example “Connection refused” or “Connection
457       reset”. 2 is reserved for all other errors, like an invalid option or a
458       nonexistent file.
459

BUGS

461       Like its authors, Ncat isn't perfect. But you can help make it better
462       by sending bug reports or even writing patches. If Ncat doesn't behave
463       the way you expect, first upgrade to the latest version available from
464       https://nmap.org. If the problem persists, do some research to
465       determine whether it has already been discovered and addressed. Try
466       Googling the error message or browsing the nmap-dev archives at
467       http://seclists.org/.
468
469       Read this full manual page as well. If nothing comes of this, mail a
470       bug report to <dev@nmap.org>. Please include everything you have
471       learned about the problem, as well as what version of Ncat you are
472       running and what operating system version it is running on. Problem
473       reports and Ncat usage questions sent to dev@nmap.org are far more
474       likely to be answered than those sent to Fyodor directly.
475
476       Code patches to fix bugs are even better than bug reports. Basic
477       instructions for creating patch files with your changes are available
478       at https://svn.nmap.org/nmap/HACKING. Patches may be sent to nmap-dev
479       (recommended) or to Fyodor directly.
480

AUTHORS

482       ·   Chris Gibson <chris@linuxops.net>
483
484       ·   Kris Katterjohn <katterjohn@gmail.com>
485
486       ·   Mixter <mixter@gmail.com>
487
488       ·   Fyodor <fyodor@nmap.org> (http://insecure.org)
489
490       The original Netcat was written by *Hobbit* <hobbit@avian.org>. While
491       Ncat isn't built on any code from the “traditional” Netcat (or any
492       other implementation), Ncat is most definitely based on Netcat in
493       spirit and functionality.
494
496   Ncat Copyright and Licensing
497       Ncat is (C) 2005–2012 Insecure.Com LLC. It is distributed as free and
498       open source software under the same license terms as our Nmap software.
499       Precise terms and further details are available from
500       https://nmap.org/man/man-legal.html.
501
502   Creative Commons License for this Ncat Guide
503       This Ncat Reference Guide is (C) 2005–2012 Insecure.Com LLC. It is
504       hereby placed under version 3.0 of the Creative Commons Attribution
505       License[1]. This allows you redistribute and modify the work as you
506       desire, as long as you credit the original source. Alternatively, you
507       may choose to treat this document as falling under the same license as
508       Ncap itself (discussed previously).
509
510   Source Code Availability and Community Contributions
511       Source is provided to this software because we believe users have a
512       right to know exactly what a program is going to do before they run it.
513       This also allows you to audit the software for security holes (none
514       have been found so far).
515
516       Source code also allows you to port Nmap (which includes Ncat) to new
517       platforms, fix bugs, and add new features. You are highly encouraged to
518       send your changes to <dev@nmap.org> for possible incorporation into the
519       main distribution. By sending these changes to Fyodor or one of the
520       Insecure.Org development mailing lists, it is assumed that you are
521       offering the Nmap Project (Insecure.Com LLC) the unlimited,
522       non-exclusive right to reuse, modify, and relicense the code. Nmap will
523       always be available open source, but this is important because the
524       inability to relicense code has caused devastating problems for other
525       Free Software projects (such as KDE and NASM). We also occasionally
526       relicense the code to third parties as discussed in the Nmap man page.
527       If you wish to specify special license conditions of your
528       contributions, just say so when you send them.
529
530   No Warranty
531       This program is distributed in the hope that it will be useful, but
532       WITHOUT ANY WARRANTY; without even the implied warranty of
533       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
534       General Public License v2.0 for more details at
535       http://www.gnu.org/licenses/gpl-2.0.html, or in the COPYING file
536       included with Nmap.
537
538   Inappropriate Usage
539       Ncat should never be installed with special privileges (e.g. suid
540       root).  That would open up a major security vulnerability as other
541       users on the system (or attackers) could use it for privilege
542       escalation.
543
544   Third-Party Software
545       This product includes software developed by the Apache Software
546       Foundation[2]. A modified version of the Libpcap portable packet
547       capture library[3] is distributed along with Ncat. The Windows version
548       of Ncat utilized the Libpcap-derived Npcap library[4] instead. Certain
549       raw networking functions use the Libdnet[5] networking library, which
550       was written by Dug Song.  A modified version is distributed with Ncat.
551       Ncat can optionally link with the OpenSSL cryptography toolkit[6] for
552       SSL version detection support. All of the third-party software
553       described in this paragraph is freely redistributable under BSD-style
554       software licenses.
555

NOTES

557        1. Creative Commons Attribution License
558           http://creativecommons.org/licenses/by/3.0/
559
560        2. Apache Software Foundation
561           http://www.apache.org
562
563        3. Libpcap portable packet capture library
564           http://www.tcpdump.org
565
566        4. Npcap library
567           http://www.npcap.org
568
569        5. Libdnet
570           http://libdnet.sourceforge.net
571
572        6. OpenSSL cryptography toolkit
573           http://www.openssl.org
574
575
576
577Ncat                              03/15/2018                           NCAT(1)
Impressum