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, SOCKS5 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 7.92 ( https://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


  -U, --unixsock             Use Unix domain sockets only


      --vsock                Use vsock 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


  -z                         Zero-I/O mode, report connection status only


      --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


      --no-shutdown          Continue half-duplex when receiving EOF on stdin


      --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", "socks4", "socks5")


      --proxy-auth <auth>    Authenticate with HTTP or SOCKS proxy server


      --proxy-dns <type>     Specify where to resolve proxy destination


      --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


      --ssl-ciphers          Cipherlist containing SSL ciphers to use


      --ssl-servername       Request distinct server name (SNI)


      --ssl-alpn             ALPN protocol list to use


      --version              Display Ncat's version information and exit

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 over IPv4 and IPv6. If port is omitted, it defaults to 31337.

PROTOCOL OPTIONS¶

-4 (IPv4 only)

-6 (IPv6 only)

-U, --unixsock (Use Unix domain sockets)

-u, --udp (Use UDP)

--sctp (Use SCTP)

--vsock (Use AF_VSOCK sockets)

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)

--ssl-ciphers cipherlist (Specify SSL ciphersuites)

--ssl-servername name (Request distinct server name)

--ssl-alpn ALPN list (Specify ALPN protocol list)

PROXY OPTIONS¶

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

--proxy-type proto (Specify proxy protocol)

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

--proxy-dns type (Specify where to resolve proxy destination)

COMMAND EXECUTION OPTIONS¶

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

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

--lua-exec file (Execute a .lua script)

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

NCAT_REMOTE_ADDR, NCAT_REMOTE_PORT

NCAT_LOCAL_ADDR, NCAT_LOCAL_PORT

NCAT_PROTO

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)

--append-output (Append output)

-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)

--no-shutdown (Do not shutdown into half-duplex mode)

-n, --nodns (Do not resolve hostnames)

-t, --telnet (Answer Telnet negotiations)

--version (Display version)

UNIX DOMAIN SOCKETS¶

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.

AF_VSOCK SOCKETS¶

The --vsock option causes Ncat to use AF_VSOCK sockets rather than network sockets. A CID must be given instead of a hostname or IP address. For example, to make a connection to the host,

ncat --vsock 2 1234

To listen on a socket:

ncat -l --vsock 1234

Both stream and datagram domain sockets are supported, but socket type availability depends on the hypervisor. Use --vsock on its own for stream sockets, or combine it with --udp for datagram sockets.

EXAMPLES¶

Connect to example.org on TCP port 8080.

Listen for connections on TCP port 8080.

Redirect TCP port 8080 on the local machine to host on port 80.

Bind to TCP port 8081 and attach /bin/bash for the world to access freely.

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.

Connect to smtphost:25 through a SOCKS4 server on port 1080.

Connect to smtphost:25 through a SOCKS5 server on port 1080.

Create an HTTP proxy server on localhost port 8888.

Send a file over TCP port 9899 from host2 (client) to host1 (server).

Transfer in the other direction, turning Ncat into a “one file” server.

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 https://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 <dev@nmap.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 dev@nmap.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 https://svn.nmap.org/nmap/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.

LEGAL NOTICES¶

NOTES¶

1.

Creative Commons Attribution License

2.

Apache Software Foundation

3.

Libpcap portable packet capture library

4.

Npcap library

5.

Libdnet

6.

OpenSSL cryptography toolkit