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Ncat Reference Guide (Man Page)
Namencat — Concatenate and redirect sockets Synopsisncat [
<OPTIONS>
...] [
<hostname>
] [
<port>
]
Ncat is a feature-packed networking utility which will read and write
data across a network from the command line. Ncat was written for the Nmap
Project and is the culmination of the currently splintered family of Netcat
incarnations. It uses both TCP and UDP for communication and 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, redirect both TCP and UDP ports to other sites, SSL support, and proxy
connections via SOCKS4 or HTTP (CONNECT method) 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.
Ncat 5.21 ( http://nmap.org/ncat )
Usage: ncat [options] [hostname] [port]
Options taking a time assume milliseconds, unless you append an 's'
(seconds), 'm' (minutes), or 'h' (hours) to the value (e.g. 30s)
-4 Use IPv4 only
-6 Use IPv6 only
-C, --crlf Use CRLF for EOL sequence
-c, --sh-exec <command> Executes specified command via /bin/sh
-e, --exec <command> Executes specified 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 specific hosts to connect to Ncat
--allowfile A file of hosts allowed to connect to Ncat
--deny Hosts to be denied 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
When passing a host parameter to Ncat, the simplest case is just to
list a single hostname or IP address. If you are supplying a range of hosts,
such as with --deny or --allow options, you
can denote the chosen range of IP addresses by appending the CIDR-style '/mask'
to the IP address. The mask must be between zero (select the whole subnet) and 32
(scan the single host specified). For example, you may use /24 to scan a class
C subnet and /16 for a class B. -
-4 (IPv4 only)
Force the use of IPv4 only (default). -
-6 (IPv6 only)
Force the use of IPv6 only. -
-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 four 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 Access Control section for information on limiting which
hosts can 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 max number of connections)
The maximum number of simultaneous connections accepted for 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 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 (Use SSL)
In client-mode Ncat, 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 Ncat, 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. Some operating systems provide a default list of
trusted certificates; these will also be used if available. Use
--ssl-trustfile to give a custom list. Use
-v one or more times to get details about
verification failures. 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, --proxy-auth is available. -
--proxy-type <proto> (Specify proxy protocol)
In client-mode, this option requests using proxy protocol <proto>
to connect through the proxy host specified by --proxy. In server-mode,
this option requests Ncat to actually act as a proxy server using the specified protocol. The currently available protocols in client-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)
Used to specify proxy authentication credentials for client-mode. For use with
--proxy-type http, the form should be user:pass. For
--proxy-type socks4, it should just be a username.
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 sent to the application and
responses sent back to the remote client over the socket. Thus,
effectively instantly making your application interactive over a
socket. Ncat will handle multiple simultaneous connections to your
specified port/application rather like inetd does. Ncat will only
accept a maximum, definable, number of simultaneous connections. 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 (so you don't have to specify the full path
for the command).
-
--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 silently dropped. 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. The syntax for hosts is
the same as for --allow. -
--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 milliseconds by default, though you can append “s”, “m”,
or “h” to the value to specify 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
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. This can be used to
“replay” sessions, etc. -
-v,
--verbose (Verbosity)
Issue Ncat with -v and it will be verbose and
display all kinds of useful connection based information. If you issue
this twice (-vv) then you will get all the code
debugging information. Issue it three times (-vvv) and
you get the connection information and the code debugging information.
-
-C,
--crlf (Use CRLF as EOL)
This option tells Ncat to try to use CRLF for line-endings if only
an LF is found. This doesn't convert all LFs to CRLFs, only if it's at
the end of the read buffer. This is useful for talking to some stringent
servers directly from a terminal in one of the many common plain-text
protocols which specify CRLF as the required EOL sequence. -
-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. -
-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)
This displays the Ncat version, release information and any
additional build information and exits.
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 example.org on port 80 ncat --sh-exec “ncat example.org 80” -l 8080 Bind to TCP port 8081 and attach /bin/bash for the world to access freely ncat --exec “/bin/bash” -l 8081 Bind a shell to TCP port 8081, limit access to hosts on a local network
and limit the maximum number of simultaneous connections to three ncat --exec “/bin/bash” --max-conns 3 --allow 192.168.0.0/24 -l 8081 Connect to 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 author, 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. |
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