NAME¶

ncat - Concatenate and redirect sockets

SYNOPSIS¶

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

DESCRIPTION¶

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 it.

OPTIONS SUMMARY¶

Ncat 5.51 ( http://nmap.org/ncat )
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


  -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


  -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               Dump session data to a file


  -x, --hex-dump             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 up to 3 times)


  -w, --wait <time>          Connect timeout


      --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")


      --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

CONNECT MODE AND LISTEN MODE¶

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. If port is omitted, it defaults to 31337.

PROTOCOL OPTIONS¶

-4 (IPv4 only) .

-6 (IPv6 only) .

-u, --udp (Use UDP) .

--sctp (Use SCTP) .

CONNECT MODE OPTIONS¶

-g hop1[,hop2,...] (Loose source routing) .

-G ptr (Set source routing pointer) .

-p port, --source-port port (Specify source port) .

-s host, --source host (Specify source address) .

LISTEN MODE OPTIONS¶

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) .

-m numconns, --max-conns numconns (Specify maximum number of connections) .

-k, --keep-open (Accept multiple connections) .

--broker (Connection brokering) .

--chat (Ad-hoc “chat server”) .

SSL OPTIONS¶

--ssl (Use SSL) .

--ssl-verify (Verify server certificates) .

--ssl-cert certfile.pem (Specify SSL certificate) .

--ssl-key keyfile.pem (Specify SSL private key) .

--ssl-trustfile cert.pem (List trusted certificates) .

PROXY OPTIONS¶

--proxy host[:port] (Specify proxy address) .

--proxy-type proto (Specify proxy protocol) .

--proxy-auth user[:pass] (Specify proxy credentials) .

COMMAND EXECUTION OPTIONS¶

-e command, --exec command (Execute command) .

-c command, --sh-exec command (Execute command via sh) .

ACCESS CONTROL OPTIONS¶

--allow host[,host,...] (Allow connections) .

--allowfile file (Allow connections from file) .

--deny host[,host,...] (Deny connections) .

--denyfile file (Deny connections from file) .

TIMING OPTIONS¶

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) .

-i time, --idle-timeout time (Specify idle timeout) .

-w time, --wait time (Specify connect timeout) .

OUTPUT OPTIONS¶

-o file, --output file (Save session data) .

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

-v, --verbose (Be verbose) .

MISC OPTIONS¶

-C, --crlf (Use CRLF as EOL) .

-h, --help (Help screen) .

--recv-only (Only receive data) .

--send-only (Only send data) .

-t, --telnet (Answer Telnet negotiations) .

--version (Display version) .

EXAMPLES¶

EXIT CODE¶

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.

BUGS¶

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 http://nmap.org. 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 http://seclists.org/. Read this full manual page as well. If nothing comes of this, mail a bug report to nmap-dev@insecure.org. 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 nmap-dev@insecure.org 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 http://nmap.org/data/HACKING. Patches may be sent to nmap-dev (recommended) or to Fyodor directly.

AUTHORS¶

The original Netcat was written by *Hobbit* hobbit@avian.org. 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.