ncat
(1)
Name
ncat - Concatenate and redirect sockets
Synopsis
ncat [OPTIONS...] [hostname] [port]
Description
Ncat Reference Guide NCAT(1)
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 6.25 ( 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
-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
-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
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--sctp Use SCTP instead of default TCP
-v, --verbose Set verbosity level (can be used up to 3 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")
--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 over IPv4 and IPv6. If port is
omitted, it defaults to 31337.
PROTOCOL OPTIONS
-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,
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or combined with --udp for datagram sockets. A
description of -U mode is in the section called "UNIX
DOMAIN SOCKETS".
-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.
CONNECT MODE OPTIONS
-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.
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) .
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.
-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
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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 hang.
--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 OPTIONS
--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.
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--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 OPTIONS
--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.
COMMAND EXECUTION OPTIONS
-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
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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.
-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.
ACCESS CONTROL OPTIONS
--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.
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) .
Set the delay interval for lines sent. This effectively
limits the number of lines that Ncat will send in the
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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.
OUTPUT OPTIONS
-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. -vvv
is the maximum level.
MISC OPTIONS
-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 input.
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-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.
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.
EXAMPLES
Connect to example.org on TCP port 8080.
ncat example.org 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 example.org 80" -l 8080 --keep-open
Bind to TCP port 8081 and attach /bin/bash for the world to
access freely.
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
192.168.0.0/24 -l 8081 --keep-open
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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
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 blue]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 blue]-
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 blue]-
https://svn.nmap.org/nmap/HACKING]. Patches may be sent to
nmap-dev (recommended) or to Fyodor directly.
AUTHORS
o Chris Gibson chris@linuxops.net
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o Kris Katterjohn katterjohn@gmail.com
o Mixter mixter@gmail.com
o Fyodor fyodor@insecure.org (blue]http://insecure.org])
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
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 blue]http://nmap.org/man/man-legal.html].
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 blue]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
nmap-dev@insecure.org 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.
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No Warranty.
This program is distributed in the hope that it will be
useful, but WITHOUT ANY WARRANTY; without even the implied
warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
PURPOSE. See the GNU General Public License v2.0 for more
details at blue]http://www.gnu.org/licenses/gpl-2.0.html],
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 escalation.
Third-Party Software
This product includes software developed by the blue]Apache
Software Foundation][2]. A modified version of the
blue]Libpcap portable packet capture library][3]. is
distributed along with Ncat. The Windows version of Ncat
utilized the Libpcap-derived blue]WinPcap library][4].
instead. Certain raw networking functions use the
blue]Libdnet][5]. networking library, which was written by
Dug Song.. A modified version is distributed with Ncat.
Ncat can optionally link with the blue]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.
ATTRIBUTES
See attributes(5) for descriptions of the following
attributes:
+---------------+------------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+------------------+
|Availability | diagnostic/nmap |
+---------------+------------------+
|Stability | Volatile |
+---------------+------------------+
NOTES
1. Creative Commons Attribution License
http://creativecommons.org/licenses/by/3.0/
2. Apache Software Foundation
http://www.apache.org
3. Libpcap portable packet capture library
http://www.tcpdump.org
4. WinPcap library
http://www.winpcap.org
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5. Libdnet
http://libdnet.sourceforge.net
6. OpenSSL cryptography toolkit
http://www.openssl.org
This software was built from source available at
https://java.net/projects/solaris-userland. The original
community source was downloaded from
http://nmap.org/dist/nmap-6.25.tgz
Further information about this software can be found on the
open source community website at http://nmap.org/.
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