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NCAT(1)			     Ncat Reference Guide		       NCAT(1)

       ncat - Concatenate and redirect sockets

       ncat [OPTIONS...] [hostname] [port]

       Ncat is a feature-packed networking utility which reads and writes data
       across networks from the command line. Ncat was written for the Nmap
       Project and is the culmination of the currently splintered family of
       Netcat incarnations. It is designed to be a reliable back-end tool to
       instantly provide network connectivity to other applications and users.
       Ncat will not only work with IPv4 and IPv6 but provides the user with a
       virtually limitless number of potential uses.

       Among Ncat's vast number of features there is the ability to chain
       Ncats together; redirection of TCP, UDP, and SCTP ports to other sites;
       SSL support; and proxy connections via SOCKS4 or HTTP proxies (with
       optional proxy authentication as well). Some general principles apply
       to most applications and thus give you the capability of instantly
       adding networking support to software that would normally never support

	   Ncat 6.46 ( )
	   Usage: ncat [options] [hostname] [port]

	   Options taking a time assume seconds. Append 'ms' for milliseconds,
	   's' for seconds, 'm' for minutes, or 'h' for hours (e.g. 500ms).
	     -4				Use IPv4 only
	     -6				Use IPv6 only
	     -U, --unixsock		Use Unix domain sockets only
	     -C, --crlf			Use CRLF for EOL sequence
	     -c, --sh-exec <command>	Executes the given command via /bin/sh
	     -e, --exec <command>	Executes the given command
		 --lua-exec <filename>	Executes the given Lua script
	     -g hop1[,hop2,...]		Loose source routing hop points (8 max)
	     -G <n>			Loose source routing hop pointer (4, 8, 12, ...)
	     -m, --max-conns <n>	Maximum <n> simultaneous connections
	     -h, --help			Display this help screen
	     -d, --delay <time>		Wait between read/writes
	     -o, --output <filename>	Dump session data to a file
	     -x, --hex-dump <filename>	Dump session data as hex to a file
	     -i, --idle-timeout <time>	Idle read/write timeout
	     -p, --source-port port	Specify source port to use
	     -s, --source addr		Specify source address to use (doesn't affect -l)
	     -l, --listen		Bind and listen for incoming connections
	     -k, --keep-open		Accept multiple connections in listen mode
	     -n, --nodns		Do not resolve hostnames via DNS
	     -t, --telnet		Answer Telnet negotiations
	     -u, --udp			Use UDP instead of default TCP
		 --sctp			Use SCTP instead of default TCP
	     -v, --verbose		Set verbosity level (can be used several times)
	     -w, --wait <time>		Connect timeout
		 --append-output	Append rather than clobber specified output files
		 --send-only		Only send data, ignoring received; quit on EOF
		 --recv-only		Only receive data, never send anything
		 --allow		Allow only given hosts to connect to Ncat
		 --allowfile		A file of hosts allowed to connect to Ncat
		 --deny			Deny given hosts from connecting to Ncat
		 --denyfile		A file of hosts denied from connecting to Ncat
		 --broker		Enable Ncat's connection brokering mode
		 --chat			Start a simple Ncat chat server
		 --proxy <addr[:port]>	Specify address of host to proxy through
		 --proxy-type <type>	Specify proxy type ("http" or "socks4" or "socks5")
		 --proxy-auth <auth>	Authenticate with HTTP or SOCKS proxy server
		 --ssl			Connect or listen with SSL
		 --ssl-cert		Specify SSL certificate file (PEM) for listening
		 --ssl-key		Specify SSL private key (PEM) for listening
		 --ssl-verify		Verify trust and domain name of certificates
		 --ssl-trustfile	PEM file containing trusted SSL certificates
		 --version		Display Ncat's version information and exit

	   See the ncat(1) manpage for full options, descriptions and usage examples

       Ncat operates in one of two primary modes: connect mode and listen
       mode. Other modes, such as the HTTP proxy server, act as special cases
       of these two. In connect mode, Ncat works as a client. In listen mode
       it is a server.

       In connect mode, the hostname and port arguments tell what to connect
       to.  hostname is required, and may be a hostname or IP address. If port
       is supplied, it must be a decimal port number. If omitted, it defaults
       to 31337..

       In listen mode, hostname and port control the address the server will
       bind to. Both arguments are optional in listen mode. If hostname is
       omitted, it defaults to listening on all available addresses over IPv4
       and IPv6. If port is omitted, it defaults to 31337.

       -4 (IPv4 only) .
	   Force the use of IPv4 only.

       -6 (IPv6 only) .
	   Force the use of IPv6 only.

       -U, --unixsock (Use Unix domain sockets) .
	   Use Unix domain sockets rather than network sockets. This option
	   may be used on its own for stream sockets, or combined with --udp
	   for datagram sockets. A description of -U mode is in the section

       -u, --udp (Use UDP) .
	   Use UDP for the connection (the default is TCP).

       --sctp (Use SCTP) .
	   Use SCTP for the connection (the default is TCP). SCTP support is
	   implemented in TCP-compatible mode.

       -g hop1[,hop2,...] (Loose source routing) .
	   Sets hops for IPv4 loose source routing. You can use -g once with a
	   comma-separated list of hops, use -g multiple times with single
	   hops to build the list, or combine the two. Hops can be given as IP
	   addresses or hostnames.

       -G ptr (Set source routing pointer) .
	   Sets the IPv4 source route “pointer” for use with -g. The argument
	   must be a multiple of 4 and no more than 28. Not all operating
	   systems support setting this pointer to anything other than four.

       -p port, --source-port port (Specify source port) .
	   Set the port number for Ncat to bind to.

       -s host, --source host (Specify source address) .
	   Set the address for Ncat to bind to.

       See the section called “ACCESS CONTROL OPTIONS” for information on
       limiting the hosts that may connect to the listening Ncat process.

       -l, --listen (Listen for connections) .
	   Listen for connections rather than connecting to a remote machine

       -m numconns, --max-conns numconns (Specify maximum number of
       connections) .
	   The maximum number of simultaneous connections accepted by an Ncat
	   instance. 100 is the default (60 on Windows).

       -k, --keep-open (Accept multiple connections) .
	   Normally a listening server accepts only one connection and then
	   quits when the connection is closed. This option makes it accept
	   multiple simultaneous connections and wait for more connections
	   after they have all been closed. It must be combined with --listen.
	   In this mode there is no way for Ncat to know when its network
	   input is finished, so it will keep running until interrupted. This
	   also means that it will never close its output stream, so any
	   program reading from Ncat and looking for end-of-file will also

       --broker (Connection brokering) .
	   Allow multiple parties to connect to a centralised Ncat server and
	   communicate with each other. Ncat can broker communication between
	   systems that are behind a NAT or otherwise unable to directly
	   connect. This option is used in conjunction with --listen, which
	   causes the --listen port to have broker mode enabled.

       --chat (Ad-hoc “chat server”) .
	   The --chat option enables chat mode, intended for the exchange of
	   text between several users. In chat mode, connection brokering is
	   turned on. Ncat prefixes each message received with an ID before
	   relaying it to the other connections. The ID is unique for each
	   connected client. This helps distinguish who sent what.
	   Additionally, non-printing characters such as control characters
	   are escaped to keep them from doing damage to a terminal.

       --ssl (Use SSL) .
	   In connect mode, this option transparently negotiates an SSL
	   session with an SSL server to securely encrypt the connection. This
	   is particularly handy for talking to SSL enabled HTTP servers, etc.

	   In server mode, this option listens for incoming SSL connections,
	   rather than plain untunneled traffic.

       --ssl-verify (Verify server certificates) .
	   In client mode, --ssl-verify is like --ssl except that it also
	   requires verification of the server certificate. Ncat comes with a
	   default set of trusted certificates in the file ca-bundle.crt.
	   --ssl-trustfile to give a custom list. Use -v one or more times to
	   get details about verification failures.  Ncat does not check for
	   revoked certificates.

	   This option has no effect in server mode.

       --ssl-cert certfile.pem (Specify SSL certificate) .
	   This option gives the location of a PEM-encoded certificate files
	   used to authenticate the server (in listen mode) or the client (in
	   connect mode). Use it in combination with --ssl-key.

       --ssl-key keyfile.pem (Specify SSL private key) .
	   This option gives the location of the PEM-encoded private key file
	   that goes with the certificate named with --ssl-cert.

       --ssl-trustfile cert.pem (List trusted certificates) .
	   This option sets a list of certificates that are trusted for
	   purposes of certificate verification. It has no effect unless
	   combined with --ssl-verify. The argument to this option is the name
	   of a PEM.  file containing trusted certificates. Typically, the
	   file will contain certificates of certification authorities, though
	   it may also contain server certificates directly. When this option
	   is used, Ncat does not use its default certificates.

       --proxy host[:port] (Specify proxy address) .
	   Requests proxying through host:port, using the protocol specified
	   by --proxy-type.

	   If no port is specified, the proxy protocol's well-known port is
	   used (1080 for SOCKS and 3128 for HTTP). However, when specifying
	   an IPv6 HTTP proxy server using the IP address rather than the
	   hostname, the port number MUST be specified as well. If the proxy
	   requires authentication, use --proxy-auth.

       --proxy-type proto (Specify proxy protocol) .
	   In connect mode, this option requests the protocol proto to connect
	   through the proxy host specified by --proxy. In listen mode, this
	   option has Ncat act as a proxy server using the specified protocol.

	   The currently available protocols in connect mode are http
	   (CONNECT) and socks4 (SOCKSv4). The only server currently supported
	   is http. If this option is not used, the default protocol is http.

       --proxy-auth user[:pass] (Specify proxy credentials) .
	   In connect mode, gives the credentials that will be used to connect
	   to the proxy server. In listen mode, gives the credentials that
	   will be required of connecting clients. For use with --proxy-type
	   http, the form should be user:pass. For --proxy-type socks4, it
	   should be a username only.

       -e command, --exec command (Execute command) .
	   Execute the specified command after a connection has been
	   established. The command must be specified as a full pathname. All
	   input from the remote client will be sent to the application and
	   responses sent back to the remote client over the socket, thus
	   making your command-line application interactive over a socket.
	   Combined with --keep-open, Ncat will handle multiple simultaneous
	   connections to your specified port/application like inetd. Ncat
	   will only accept a maximum, definable, number of simultaneous
	   connections controlled by the -m option. By default this is set to
	   100 (60 on Windows).

       -c command, --sh-exec command (Execute command via sh) .
	   Same as -e, except it tries to execute the command via /bin/sh.
	   This means you don't have to specify the full path for the command,
	   and shell facilities like environment variables are available.

       --lua-exec file (Execute a .lua script) .
	   Runs the specified file as a Lua script after a connection has been
	   established, using a built-in interpreter. Both the script's
	   standard input and the standard output are redirected to the
	   connection data streams.

       All exec options add the following variables to the child's

	   The IP address and port number of the remote host. In connect mode,
	   it's the target's address; in listen mode, it's the client's

	   The IP address and port number of the local end of the connection.

	   The protocol in use: one of TCP, UDP, and SCTP.

       --allow host[,host,...] (Allow connections) .
	   The list of hosts specified will be the only hosts allowed to
	   connect to the Ncat process. All other connection attempts will be
	   disconnected. In case of a conflict between --allow and --deny,
	   --allow takes precedence. Host specifications follow the same
	   syntax used by Nmap.

       --allowfile file (Allow connections from file) .
	   This has the same functionality as --allow, except that the allowed
	   hosts are provided in a new-line delimited allow file, rather than
	   directly on the command line.

       --deny host[,host,...] (Deny connections) .
	   Issue Ncat with a list of hosts that will not be allowed to connect
	   to the listening Ncat process. Specified hosts will have their
	   session silently terminated if they try to connect. In case of a
	   conflict between --allow and --deny, --allow takes precedence. Host
	   specifications follow the same syntax used by Nmap.

       --denyfile file (Deny connections from file) .
	   This is the same functionality as --deny, except that excluded
	   hosts are provided in a new-line delimited deny file, rather than
	   directly on the command line.

       These options accept a time parameter. This is specified in seconds by
       default, though you can append ms, s, m, or h to the value to specify
       milliseconds, seconds, minutes, or hours.

       -d time, --delay time (Specify line delay) .
	   Set the delay interval for lines sent. This effectively limits the
	   number of lines that Ncat will send in the specified period. This
	   may be useful for low-bandwidth sites, or have other uses such as
	   coping with annoying iptables --limit options.

       -i time, --idle-timeout time (Specify idle timeout) .
	   Set a fixed timeout for idle connections. If the idle timeout is
	   reached, the connection is terminated.

       -w time, --wait time (Specify connect timeout) .
	   Set a fixed timeout for connection attempts.

       -o file, --output file (Save session data) .
	   Dump session data to a file

       -x file, --hex-dump file (Save session data in hex) .
	   Dump session data in hex to a file.

       --append-output (Append output) .
	   Issue Ncat with --append-ouput along with -o and/or -x and it will
	   append the resulted output rather than truncating the specified
	   output files.

       -v, --verbose (Be verbose) .
	   Issue Ncat with -v and it will be verbose and display all kinds of
	   useful connection based information. Use more than once (-vv,
	   -vvv...) for greater verbosity.

       -C, --crlf (Use CRLF as EOL) .
	   This option tells Ncat to convert LF.  line endings to CRLF.	 when
	   taking input from standard input..  This is useful for talking to
	   some stringent servers directly from a terminal in one of the many
	   common plain-text protocols that use CRLF for end-of-line.

       -h, --help (Help screen) .
	   Displays a short help screen with common options and parameters,
	   and then exits.

       --recv-only (Only receive data) .
	   If this option is passed, Ncat will only receive data and will not
	   try to send anything.

       --send-only (Only send data) .
	   If this option is passed, then Ncat will only send data and will
	   ignore anything received. This option also causes Ncat to close the
	   network connection and terminate after EOF is received on standard

       -t, --telnet (Answer Telnet negotiations) .
	   Handle DO/DONT WILL/WONT Telnet negotiations. This makes it
	   possible to script Telnet sessions with Ncat.

       --version (Display version) .
	   Displays the Ncat version number and exits.

       The -U option (same as --unixsock) causes Ncat to use Unix domain
       sockets rather than network sockets. Unix domain sockets exist as an
       entry in the filesystem. You must give the name of a socket to connect
       to or to listen on. For example, to make a connection,

       ncat -U ~/unixsock

       To listen on a socket:

       ncat -l -U ~/unixsock

       Listen mode will create the socket if it doesn't exist. The socket will
       continue to exist after the program ends.

       Both stream and datagram domain sockets are supported. Use -U on its
       own for stream sockets, or combine it with --udp for datagram sockets.
       Datagram sockets require a source socket to connect from. By default, a
       source socket with a random filename will be created as needed, and
       deleted when the program ends. Use the --source with a path to use a
       source socket with a specific name.

       Connect to on TCP port 8080.
	   ncat 8080

       Listen for connections on TCP port 8080.
	   ncat -l 8080

       Redirect TCP port 8080 on the local machine to host on port 80.
	   ncat --sh-exec "ncat 80" -l 8080 --keep-open

       Bind to TCP port 8081 and attach /bin/bash for the world to access
	   ncat --exec "/bin/bash" -l 8081 --keep-open

       Bind a shell to TCP port 8081, limit access to hosts on a local
       network, and limit the maximum number of simultaneous connections to 3.
	   ncat --exec "/bin/bash" --max-conns 3 --allow -l
	   8081 --keep-open

       Connect to smtphost:25 through a SOCKS4 server on port 1080.
	   ncat --proxy socks4host --proxy-type socks4 --proxy-auth user
	   smtphost 25

       Create an HTTP proxy server on localhost port 8888.
	   ncat -l --proxy-type http localhost 8888

       Send a file over TCP port 9899 from host2 (client) to host1 (server).
	   HOST1$ ncat -l 9899 > outputfile

	   HOST2$ ncat HOST1 9899 < inputfile

       Transfer in the other direction, turning Ncat into a “one file” server.
	   HOST1$ ncat -l 9899 < inputfile

	   HOST2$ ncat HOST1 9899 > outputfile

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

       Like its authors, Ncat isn't perfect. But you can help make it better
       by sending bug reports or even writing patches. If Ncat doesn't behave
       the way you expect, first upgrade to the latest version available from If the problem persists, do some research to determine
       whether it has already been discovered and addressed. Try Googling the
       error message or browsing the nmap-dev archives at  Read this full manual page as well. If nothing
       comes of this, mail a bug report to <>. Please include
       everything you have learned about the problem, as well as what version
       of Ncat you are running and what operating system version it is running
       on. Problem reports and Ncat usage questions sent to are
       far more likely to be answered than those sent to Fyodor directly.

       Code patches to fix bugs are even better than bug reports. Basic
       instructions for creating patch files with your changes are available
       at Patches may be sent to nmap-dev
       (recommended) or to Fyodor directly.

       ·   Chris Gibson <>

       ·   Kris Katterjohn <>

       ·   Mixter <>

       ·   Fyodor <> (

       The original Netcat was written by *Hobbit* <>. While
       Ncat isn't built on any code from the “traditional” Netcat (or any
       other implementation), Ncat is most definitely based on Netcat in
       spirit and functionality.

   Ncat Copyright and Licensing
       Ncat is (C) 2005–2012 Insecure.Com LLC. It is distributed as free and
       open source software under the same license terms as our Nmap software.
       Precise terms and further details are available from

   Creative Commons License for this Ncat Guide
       This Ncat Reference Guide is (C) 2005–2012 Insecure.Com LLC. It is
       hereby placed under version 3.0 of the Creative Commons Attribution
       License[1]. This allows you redistribute and modify the work as you
       desire, as long as you credit the original source. Alternatively, you
       may choose to treat this document as falling under the same license as
       Ncap itself (discussed previously).

   Source Code Availability and Community Contributions
       Source is provided to this software because we believe users have a
       right to know exactly what a program is going to do before they run it.
       This also allows you to audit the software for security holes (none
       have been found so far).

       Source code also allows you to port Nmap (which includes Ncat) to new
       platforms, fix bugs, and add new features. You are highly encouraged to
       send your changes to <> for possible incorporation into the
       main distribution. By sending these changes to Fyodor or one of the
       Insecure.Org development mailing lists, it is assumed that you are
       offering the Nmap Project (Insecure.Com LLC) the unlimited,
       non-exclusive right to reuse, modify, and relicense the code. Nmap will
       always be available open source,.  but this is important because the
       inability to relicense code has caused devastating problems for other
       Free Software projects (such as KDE and NASM). We also occasionally
       relicense the code to third parties as discussed in the Nmap man page.
       If you wish to specify special license conditions of your
       contributions, just say so when you send them.

   No Warranty.
       This program is distributed in the hope that it will be useful, but
       WITHOUT ANY WARRANTY; without even the implied warranty of
       General Public License v2.0 for more details at, or in the COPYING file
       included with Nmap.

   Inappropriate Usage
       Ncat should never be installed with special privileges (e.g. suid
       root)..	That would open up a major security vulnerability as other
       users on the system (or attackers) could use it for privilege

   Third-Party Software
       This product includes software developed by the Apache Software
       Foundation[2]. A modified version of the Libpcap portable packet
       capture library[3].  is distributed along with Ncat. The Windows
       version of Ncat utilized the Libpcap-derived WinPcap library[4].
       instead. Certain raw networking functions use the Libdnet[5].
       networking library, which was written by Dug Song..  A modified version
       is distributed with Ncat. Ncat can optionally link with the OpenSSL
       cryptography toolkit[6].	 for SSL version detection support. All of the
       third-party software described in this paragraph is freely
       redistributable under BSD-style software licenses.

	1. Creative Commons Attribution License

	2. Apache Software Foundation

	3. Libpcap portable packet capture library

	4. WinPcap library

	5. Libdnet

	6. OpenSSL cryptography toolkit

Ncat				  04/17/2014			       NCAT(1)

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