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 5.51 ( http://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 -C, --crlf Use CRLF for EOL sequence
37 -c, --sh-exec <command> Executes the given command via /bin/sh
38 -e, --exec <command> Executes the given command
39 -g hop1[,hop2,...] Loose source routing hop points (8 max)
40 -G <n> Loose source routing hop pointer (4, 8, 12, ...)
41 -m, --max-conns <n> Maximum <n> simultaneous connections
42 -h, --help Display this help screen
43 -d, --delay <time> Wait between read/writes
44 -o, --output Dump session data to a file
45 -x, --hex-dump Dump session data as hex to a file
46 -i, --idle-timeout <time> Idle read/write timeout
47 -p, --source-port port Specify source port to use
48 -s, --source addr Specify source address to use (doesn´t affect -l)
49 -l, --listen Bind and listen for incoming connections
50 -k, --keep-open Accept multiple connections in listen mode
51 -n, --nodns Do not resolve hostnames via DNS
52 -t, --telnet Answer Telnet negotiations
53 -u, --udp Use UDP instead of default TCP
54 --sctp Use SCTP instead of default TCP
55 -v, --verbose Set verbosity level (can be used up to 3 times)
56 -w, --wait <time> Connect timeout
57 --send-only Only send data, ignoring received; quit on EOF
58 --recv-only Only receive data, never send anything
59 --allow Allow only given hosts to connect to Ncat
60 --allowfile A file of hosts allowed to connect to Ncat
61 --deny Deny given hosts from connecting to Ncat
62 --denyfile A file of hosts denied from connecting to Ncat
63 --broker Enable Ncat´s connection brokering mode
64 --chat Start a simple Ncat chat server
65 --proxy <addr[:port]> Specify address of host to proxy through
66 --proxy-type <type> Specify proxy type ("http" or "socks4")
67 --proxy-auth <auth> Authenticate with HTTP or SOCKS proxy server
68 --ssl Connect or listen with SSL
69 --ssl-cert Specify SSL certificate file (PEM) for listening
70 --ssl-key Specify SSL private key (PEM) for listening
71 --ssl-verify Verify trust and domain name of certificates
72 --ssl-trustfile PEM file containing trusted SSL certificates
73 --version Display Ncat´s version information and exit
74 See the ncat(1) manpage for full options, descriptions and usage examples
76
79 Ncat operates in one of two primary modes: connect mode and listen
80 mode. Other modes, such as the HTTP proxy server, act as special cases
81 of these two. In connect mode, Ncat works as a client. In listen mode
82 it is a server.
83 In connect mode, the hostname and port arguments tell what to connect
85 to. hostname is required, and may be a hostname or IP address. If port
86 is supplied, it must be a decimal port number. If omitted, it defaults
87 to 31337..
88 In listen mode, hostname and port control the address the server will
90 bind to. Both arguments are optional in listen mode. If hostname is
91 omitted, it defaults to listening on all available addresses. If port
92 is omitted, it defaults to 31337.
93
95 -4 (IPv4 only) .
96 Force the use of IPv4 only (default).
97 -6 (IPv6 only) .
99 Force the use of IPv6 only.
100 -u, --udp (Use UDP) .
102 Use UDP for the connection (the default is TCP).
103 --sctp (Use SCTP) .
105 Use SCTP for the connection (the default is TCP). SCTP support is
106 implemented in TCP-compatible mode.
107
109 -g hop1[,hop2,...] (Loose source routing) .
110 Sets hops for IPv4 loose source routing. You can use -g once with a
111 comma-separated list of hops, use -g multiple times with single
112 hops to build the list, or combine the two. Hops can be given as IP
113 addresses or hostnames.
114 -G ptr (Set source routing pointer) .
116 Sets the IPv4 source route “pointer” for use with -g. The argument
117 must be a multiple of 4 and no more than 28. Not all operating
118 systems support setting this pointer to anything other than four.
119 -p port, --source-port port (Specify source port) .
121 Set the port number for Ncat to bind to.
122 -s host, --source host (Specify source address) .
124 Set the address for Ncat to bind to.
125
127 See the section called “ACCESS CONTROL OPTIONS” for information on
128 limiting the hosts that may connect to the listening Ncat process.
129 -l, --listen (Listen for connections) .
131 Listen for connections rather than connecting to a remote machine
132 -m numconns, --max-conns numconns (Specify maximum number of
134 connections) .
135 The maximum number of simultaneous connections accepted by an Ncat
136 instance. 100 is the default.
137 -k, --keep-open (Accept multiple connections) .
139 Normally a listening server accepts only one connection and then
140 quits when the connection is closed. This option makes it accept
141 multiple simultaneous connections and wait for more connections
142 after they have all been closed. It must be combined with --listen.
143 In this mode there is no way for Ncat to know when its network
144 input is finished, so it will keep running until interrupted. This
145 also means that it will never close its output stream, so any
146 program reading from Ncat and looking for end-of-file will also
147 hang.
148 --broker (Connection brokering) .
150 Allow multiple parties to connect to a centralised Ncat server and
151 communicate with each other. Ncat can broker communication between
152 systems that are behind a NAT or otherwise unable to directly
153 connect. This option is used in conjunction with --listen, which
154 causes the --listen port to have broker mode enabled.
155 --chat (Ad-hoc “chat server”) .
157 The --chat option enables chat mode, intended for the exchange of
158 text between several users. In chat mode, connection brokering is
159 turned on. Ncat prefixes each message received with an ID before
160 relaying it to the other connections. The ID is unique for each
161 connected client. This helps distinguish who sent what.
162 Additionally, non-printing characters such as control characters
163 are escaped to keep them from doing damage to a terminal.
164
166 --ssl (Use SSL) .
167 In connect mode, this option transparently negotiates an SSL
168 session with an SSL server to securely encrypt the connection. This
169 is particularly handy for talking to SSL enabled HTTP servers, etc.
170 In server mode, this option listens for incoming SSL connections,
172 rather than plain untunneled traffic.
173 --ssl-verify (Verify server certificates) .
175 In client mode, --ssl-verify is like --ssl except that it also
176 requires verification of the server certificate. Ncat comes with a
177 default set of trusted certificates in the file ca-bundle.crt.
178 --ssl-trustfile to give a custom list. Use -v one or more times to
179 get details about verification failures.
180 This option has no effect in server mode.
182 --ssl-cert certfile.pem (Specify SSL certificate) .
184 This option gives the location of a PEM-encoded certificate files
185 used to authenticate the server (in listen mode) or the client (in
186 connect mode). Use it in combination with --ssl-key.
187 --ssl-key keyfile.pem (Specify SSL private key) .
189 This option gives the location of the PEM-encoded private key file
190 that goes with the certificate named with --ssl-cert.
191 --ssl-trustfile cert.pem (List trusted certificates) .
193 This option sets a list of certificates that are trusted for
194 purposes of certificate verification. It has no effect unless
195 combined with --ssl-verify. The argument to this option is the name
196 of a PEM. file containing trusted certificates. Typically, the
197 file will contain certificates of certification authorities, though
198 it may also contain server certificates directly. When this option
199 is used, Ncat does not use its default certificates.
200
202 --proxy host[:port] (Specify proxy address) .
203 Requests proxying through host:port, using the protocol specified
204 by --proxy-type.
205 If no port is specified, the proxy protocol´s well-known port is
207 used (1080 for SOCKS and 3128 for HTTP). However, when specifying
208 an IPv6 HTTP proxy server using the IP address rather than the
209 hostname, the port number MUST be specified as well. If the proxy
210 requires authentication, use --proxy-auth.
211 --proxy-type proto (Specify proxy protocol) .
213 In connect mode, this option requests the protocol proto to connect
214 through the proxy host specified by --proxy. In listen mode, this
215 option has Ncat act as a proxy server using the specified protocol.
216 The currently available protocols in connect mode are http
218 (CONNECT) and socks4 (SOCKSv4). The only server currently supported
219 is http. If this option is not used, the default protocol is http.
220 --proxy-auth user[:pass] (Specify proxy credentials) .
222 In connect mode, gives the credentials that will be used to connect
223 to the proxy server. In listen mode, gives the credentials that
224 will be required of connecting clients. For use with --proxy-type
225 http, the form should be user:pass. For --proxy-type socks4, it
226 should be a username only.
227
229 -e command, --exec command (Execute command) .
230 Execute the specified command after a connection has been
231 established. The command must be specified as a full pathname. All
232 input from the remote client will be sent to the application and
233 responses sent back to the remote client over the socket, thus
234 making your command-line application interactive over a socket.
235 Combined with --keep-open, Ncat will handle multiple simultaneous
236 connections to your specified port/application like inetd. Ncat
237 will only accept a maximum, definable, number of simultaneous
238 connections controlled by the -m option. By default this is set to
239 100.
240 -c command, --sh-exec command (Execute command via sh) .
242 Same as -e, except it tries to execute the command via /bin/sh.
243 This means you don´t have to specify the full path for the command,
244 and shell facilities like environment variables are available.
245
247 --allow host[,host,...] (Allow connections) .
248 The list of hosts specified will be the only hosts allowed to
249 connect to the Ncat process. All other connection attempts will be
250 disconnected. In case of a conflict between --allow and --deny,
251 --allow takes precedence. Host specifications follow the same
252 syntax used by Nmap.
253 --allowfile file (Allow connections from file) .
255 This has the same functionality as --allow, except that the allowed
256 hosts are provided in a new-line delimited allow file, rather than
257 directly on the command line.
258 --deny host[,host,...] (Deny connections) .
260 Issue Ncat with a list of hosts that will not be allowed to connect
261 to the listening Ncat process. Specified hosts will have their
262 session silently terminated if they try to connect. be
263 disconnected. In case of a conflict between --allow and --deny,
264 --allow takes precedence. Host specifications follow the same
265 syntax used by Nmap.
266 --denyfile file (Deny connections from file) .
268 This is the same functionality as --deny, except that excluded
269 hosts are provided in a new-line delimited deny file, rather than
270 directly on the command line.
271
273 These options accept a time parameter. This is specified in seconds by
274 default, though you can append ms, s, m, or h to the value to specify
275 milliseconds, seconds, minutes, or hours.
276 -d time, --delay time (Specify line delay) .
278 Set the delay interval for lines sent. This effectively limits the
279 number of lines that Ncat will send in the specified period. This
280 may be useful for low-bandwidth sites, or have other uses such as
281 coping with annoying iptables --limit options.
282 -i time, --idle-timeout time (Specify idle timeout) .
284 Set a fixed timeout for idle connections. If the idle timeout is
285 reached, the connection is terminated.
286 -w time, --wait time (Specify connect timeout) .
288 Set a fixed timeout for connection attempts.
289
291 -o file, --output file (Save session data) .
292 Dump session data to a file
293 -x file, --hex-dump file (Save session data in hex) .
295 Dump session data in hex to a file. This can be used to “replay”
296 sessions.
297 -v, --verbose (Be verbose) .
299 Issue Ncat with -v and it will be verbose and display all kinds of
300 useful connection based information. Use more than once (-vv, -vvv)
301 for greater verbosity. -vvv is the maximum level.
302
304 -C, --crlf (Use CRLF as EOL) .
305 This option tells Ncat to convert LF. line endings to CRLF. when
306 taking input from standard input.. This is useful for talking to
307 some stringent servers directly from a terminal in one of the many
308 common plain-text protocols that use CRLF for end-of-line.
309 -h, --help (Help screen) .
311 Displays a short help screen with common options and parameters,
312 and then exits.
313 --recv-only (Only receive data) .
315 If this option is passed, Ncat will only receive data and will not
316 try to send anything.
317 --send-only (Only send data) .
319 If this option is passed, then Ncat will only send data and will
320 ignore anything received. This option also causes Ncat to close the
321 network connection and terminate after EOF is received on standard
322 input.
323 -t, --telnet (Answer Telnet negotiations) .
325 Handle DO/DONT WILL/WONT Telnet negotiations. This makes it
326 possible to script Telnet sessions with Ncat.
327 --version (Display version) .
329 Displays the Ncat version number and exits.
330
332 ncat example.org 8080.RE
333 ncat -l 8080.RE
335 ncat --sh-exec "ncat example.org 80" -l 8080 --keep-open.RE
337 ncat --exec "/bin/bash" -l 8081 --keep-open.RE
339 ncat --exec "/bin/bash" --max-conns 3 --allow
341 192.168.0.0/24 -l 8081 --keep-open.RE
342 ncat --proxy socks4host --proxy-type socks4
344 --proxy-auth user smtphost 25.RE
345 ncat -l --proxy-type http localhost 8888.RE
347 HOST1$ ncat -l 9899 > outputfile
349 HOST2$ ncat HOST1 9899 < inputfile
351 HOST1$ ncat -l 9899 < inputfile
353 HOST2$ ncat HOST1 9899 > outputfile
355
357 The exit code reflects whether a connection was made and completed
358 successfully. 0 means there was no error. 1 means there was a network
359 error of some kind, for example “Connection refused” or “Connection
360 reset”. 2 is reserved for all other errors, like an invalid option or a
361 nonexistent file.
362
364 Like its authors, Ncat isn´t perfect. But you can help make it better
365 by sending bug reports or even writing patches. If Ncat doesn´t behave
366 the way you expect, first upgrade to the latest version available from
367 http://nmap.org. If the problem persists, do some research to determine
368 whether it has already been discovered and addressed. Try Googling the
369 error message or browsing the nmap-dev archives at
370 http://seclists.org/. Read this full manual page as well. If nothing
371 comes of this, mail a bug report to nmap-dev@insecure.org. Please
372 include everything you have learned about the problem, as well as what
373 version of Ncat you are running and what operating system version it is
374 running on. Problem reports and Ncat usage questions sent to
375 nmap-dev@insecure.org are far more likely to be answered than those
376 sent to Fyodor directly.
377 Code patches to fix bugs are even better than bug reports. Basic
379 instructions for creating patch files with your changes are available
380 at http://nmap.org/data/HACKING. Patches may be sent to nmap-dev
381 (recommended) or to Fyodor directly.
382
384 · Chris Gibson chris@linuxops.net
385 · Kris Katterjohn katterjohn@gmail.com
387 · Mixter mixter@gmail.com
389 · Fyodor fyodor@insecure.org (http://insecure.org)
391 The original Netcat was written by *Hobbit* hobbit@avian.org. While
393 Ncat isn´t built on any code from the “traditional” Netcat (or any
394 other implementation), Ncat is most definitely based on Netcat in
395 spirit and functionality.
396Ncat 02/11/2011 NCAT(1)