'\" te .\" Copyright (c) 1996 David Sacerdote All rights reserved. .\" Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. 3. The name of the author may not be used to endorse or promote products derived from this .\" software without specific prior written permission THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 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All Rights Reserved. .TH NC 1 "Feb 17, 2023" .SH NAME nc \- arbitrary TCP and UDP connections and listens .SH SYNOPSIS .nf \fBnc\fR \fB-h\fR .fi .LP .nf \fBnc\fR [\fB-46dnrtuvz\fR] [\fB-i\fR \fIinterval\fR] [\fB-P\fR \fIproxy_username\fR] [\fB-p\fR \fIport\fR] [\fB-s\fR \fIsource_ip_address\fR] [\fB-T\fR \fIToS\fR] [\fB-w\fR \fItimeout\fR] [\fB-X\fR \fIproxy_protocol\fR] [\fB-x\fR \fIproxy_address\fR[:\fIport\fR]] \fIhostname\fR \fIport_list\fR .fi .LP .nf \fBnc\fR \fB-l\fR [\fB-46Ddnrtuvz\fR] [\fB-i\fR \fIinterval\fR] [\fB-T\fR \fIToS\fR] [\fIhostname\fR] \fIport\fR .fi .LP .nf \fBnc\fR \fB-l\fR [\fB-46Ddnrtuvz\fR] [\fB-i\fR \fIinterval\fR] [\fB-T\fR \fIToS\fR] \fB-p\fR \fIport\fR .fi .LP .nf \fBnc\fR \fB-U\fR [\fB-Ddtvz\fR] [\fB-i\fR \fIinterval\fR] [\fB-w\fR \fItimeout\fR] \fIpath\fR .fi .LP .nf \fBnc\fR \fB-Ul\fR [\fB-46Ddktv\fR] [\fB-i\fR \fIinterval\fR] \fIpath\fR .fi .SH DESCRIPTION The \fBnc\fR (or \fBnetcat\fR) utility is used for a variety of tasks associated with TCP or UDP. \fBnc\fR can open TCP connections, send UDP packets, listen on arbitrary TCP and UDP ports, perform port scanning, and deal with both IPv4 and IPv6. Unlike \fBtelnet\fR(1), \fBnc\fR scripts nicely, and separates error messages onto standard error instead of sending them to standard output. .sp .LP The \fBnc\fR command is often used for the following tasks: .RS +4 .TP .ie t \(bu .el o simple TCP proxies .RE .RS +4 .TP .ie t \(bu .el o shell-script based HTTP clients and servers .RE .RS +4 .TP .ie t \(bu .el o network daemon testing .RE .RS +4 .TP .ie t \(bu .el o a SOCKS or HTTP \fBProxyCommand\fR for \fBssh\fR(1) .RE .SH OPTIONS The following options are supported: .sp .ne 2 .na \fB\fB-4\fR\fR .ad .sp .6 .RS 4n Force \fBnc\fR to use IPv4 addresses only. .RE .sp .ne 2 .na \fB\fB-6\fR\fR .ad .sp .6 .RS 4n Force \fBnc\fR to use IPv6 addresses only. .RE .sp .ne 2 .na \fB\fB-D\fR\fR .ad .sp .6 .RS 4n Enable debugging on the socket. .RE .sp .ne 2 .na \fB\fB-d\fR\fR .ad .sp .6 .RS 4n Do not attempt to read from \fBstdin\fR. .RE .sp .ne 2 .na \fB\fB-h\fR\fR .ad .sp .6 .RS 4n Print \fBnc\fR help. .RE .sp .ne 2 .na \fB\fB-i\fR \fIinterval\fR\fR .ad .sp .6 .RS 4n Specify a delay time of \fIinterval\fR between lines of text sent and received. This option also causes a delay time between connections to multiple ports. .RE .sp .ne 2 .na \fB\fB-k\fR\fR .ad .sp .6 .RS 4n Force \fBnc\fR to listen for another connection after its current connection is closed. .sp It is an error to use this option without the \fB-l\fR option. .RE .sp .ne 2 .na \fB\fB-l\fR\fR .ad .sp .6 .RS 4n Listen for an incoming connection rather than initiate a connection to a remote host. .sp It is an error to use this option in conjunction with the \fB-s\fR or \fB-z\fR options. Additionally, any \fItimeout\fR specified with the \fB-w\fR option is ignored. .RE .sp .ne 2 .na \fB\fB-n\fR\fR .ad .sp .6 .RS 4n Do not do any naming or service lookups on any addresses, hostnames, or ports. .sp Use of this option means that \fIhostname\fR and \fIport\fR arguments are restricted to numeric values. .sp If used with \fB-v\fR option all addresses and ports are printed in numeric form, in addition to the restriction imposed on the arguments. This option does not have any effect when used in conjunction with the \fB-U\fR option. .RE .sp .ne 2 .na \fB\fB-P\fR \fIproxy_username\fR\fR .ad .sp .6 .RS 4n Specify a username (\fIproxy_username\fR) to present to a proxy server that requires authentication. If \fIproxy_username\fR is not specified, authentication is not attempted. Proxy authentication is only supported for \fBHTTP CONNECT\fR proxies at present. .sp It is an error to use this option in conjunction with the \fB-l\fR option. .RE .sp .ne 2 .na \fB\fB-p\fR \fIport\fR\fR .ad .sp .6 .RS 4n When used without \fB-l\fR option, specify the source port \fBnc\fR should use, subject to privilege restrictions and availability. When used with the \fB-l\fR option, set the listen port. .sp This option can be used with \fB-l\fR option only provided global port argument is not specified. .RE .sp .ne 2 .na \fB\fB-r\fR\fR .ad .sp .6 .RS 4n Choose source or destination ports randomly instead of sequentially within a range or in the order that the system assigns them. .sp It is an error to use this option in conjunction with the \fB-l\fR option. .RE .sp .ne 2 .na \fB\fB-s\fR \fIsource_ip_address\fR\fR .ad .sp .6 .RS 4n Specify the IP of the interface which is used to send the packets. .sp It is an error to use this option in conjunction with the \fB-l\fR option. .RE .sp .ne 2 .na \fB\fB-T\fR \fIToS\fR\fR .ad .sp .6 .RS 4n Specify IP Type of Service (\fBToS\fR) for the connection. Valid values are the tokens: \fBlowdelay\fR, \fBthroughput\fR, \fBreliability\fR, or an 8-bit hexadecimal value preceded by \fB0x\fR. .RE .sp .ne 2 .na \fB\fB-t\fR\fR .ad .sp .6 .RS 4n Cause \fBnc\fR to send \fIRFC 854\fR \fBDON'T\fR and \fBWON'T\fR responses to \fIRFC 854\fR \fBDO\fR and \fBWILL\fR requests. This makes it possible to use \fBnc\fR to script \fBtelnet\fR sessions. .RE .sp .ne 2 .na \fB\fB-U\fR\fR .ad .sp .6 .RS 4n Specify the use of Unix Domain Sockets. If you specify this option without \fB-l\fR, \fBnc\fR, it becomes \fBAF_UNIX\fR client. If you specify this option with the \fB-l\fR option, a \fBAF_UNIX\fR server is created. .sp Use of this option requires that a single argument of a valid Unix domain path has to be provided to \fBnc\fR, not a host name or port. .RE .sp .ne 2 .na \fB\fB-u\fR\fR .ad .sp .6 .RS 4n Use UDP instead of the default option of TCP. .RE .sp .ne 2 .na \fB\fB-v\fR\fR .ad .sp .6 .RS 4n Specify verbose output. .RE .sp .ne 2 .na \fB\fB-w\fR \fItimeout\fR\fR .ad .sp .6 .RS 4n Silently close the connection if a connection and \fBstdin\fR are idle for more than \fItimeout\fR seconds. .sp This option has no effect on the \fB-l\fR option, that is, \fBnc\fR listens forever for a connection, with or without the \fB-w\fR flag. The default is no timeout. .RE .sp .ne 2 .na \fB\fB-X\fR \fIproxy_protocol\fR\fR .ad .sp .6 .RS 4n Use the specified protocol when talking to the proxy server. Supported protocols are \fB4\fR (\fBSOCKS v.4\fR), \fB5\fR (\fBSOCKS v.5\fR) and \fBconnect\fR (\fBHTTP\fR proxy). If the protocol is not specified, \fBSOCKS v.5\fR is used. .sp It is an error to use this option in conjunction with the \fB-l\fR option. .RE .sp .ne 2 .na \fB\fB-x\fR \fIproxy_address\fR[:\fIport\fR]\fR .ad .sp .6 .RS 4n Request connection to \fIhostname\fR using a proxy at \fIproxy_address\fR and \fIport\fR. If \fIport\fR is not specified, the well-known port for the proxy protocol is used (\fB1080\fR for \fBSOCKS\fR, \fB3128\fR for \fBHTTP\fR). .sp It is an error to use this option in conjunction with the \fB-l\fR option. .RE .sp .ne 2 .na \fB\fB-z\fR\fR .ad .sp .6 .RS 4n Scan for listening daemons, without sending any data to them. .sp It is an error to use this option in conjunction with the \fB-l\fR option. .RE .SH OPERANDS The following operands are supported: .sp .ne 2 .na \fB\fIhostname\fR\fR .ad .RS 13n Specify host name. .sp \fIhostname\fR can be a numerical IP address or a symbolic hostname (unless the \fB-n\fR option is specified). .sp In general, \fIhostname\fR must be specified, unless the \fB-l\fR option is given or \fB-U\fR is used (in which case the argument is a path). If \fIhostname\fR argument is specified with \fB-l\fR option then \fIport\fR argument must be given as well and \fBnc\fR tries to bind to that address and port. If \fIhostname\fR argument is not specified with \fB-l\fR option then \fBnc\fR tries to listen on a wildcard socket for given \fIport\fR. .RE .sp .ne 2 .na \fB\fIpath\fR\fR .ad .RS 13n Specify pathname. .RE .sp .ne 2 .na \fB\fIport\fR\fR .ad .br .na \fB\fIport_list\fR\fR .ad .RS 13n Specify port. .sp \fIport_list\fR can be specified as single integers, ranges or combinations of both. Specify ranges in the form of \fInn-mm\fR. The \fIport_list\fR must have at least one member, but can have multiple ports/ranges separated by commas. .sp In general, a destination port must be specified, unless the \fB-U\fR option is given, in which case a Unix Domain Socket path must be specified instead of \fIhostname\fR. .RE .SH USAGE .SS "Client/Server Model" It is quite simple to build a very basic client/server model using \fBnc\fR. On one console, start \fBnc\fR listening on a specific port for a connection. For example, the command: .sp .in +2 .nf $ nc -l 1234 .fi .in -2 .sp .sp .LP listens on port \fB1234\fR for a connection. On a second console (or a second machine), connect to the machine and port to which \fBnc\fR is listening: .sp .in +2 .nf $ nc 127.0.0.1 1234 .fi .in -2 .sp .sp .LP There should now be a connection between the ports. Anything typed at the second console is concatenated to the first, and vice-versa. After the connection has been set up, \fBnc\fR does not really care which side is being used as a \fBserver\fR and which side is being used as a \fBclient\fR. The connection can be terminated using an \fBEOF\fR (Ctrl/d). .SS "Data Transfer" The example in the previous section can be expanded to build a basic data transfer model. Any information input into one end of the connection is output to the other end, and input and output can be easily captured in order to emulate file transfer. .sp .LP Start by using \fBnc\fR to listen on a specific port, with output captured into a file: .sp .in +2 .nf $ nc -l 1234 > filename.out .fi .in -2 .sp .sp .LP Using a second machine, connect to the listening \fBnc\fR process, feeding it the file which is to be transferred: .sp .in +2 .nf $ nc host.example.com 1234 < filename.in .fi .in -2 .sp .sp .LP After the file has been transferred, the connection closes automatically. .SS "Talking to Servers" It is sometimes useful to talk to servers \fBby hand\fR rather than through a user interface. It can aid in troubleshooting, when it might be necessary to verify what data a server is sending in response to commands issued by the client. .sp .LP For example, to retrieve the home page of a web site: .sp .in +2 .nf $ echo -n "GET / HTTP/1.0\er\en\er\en" | nc host.example.com 80 .fi .in -2 .sp .sp .LP This also displays the headers sent by the web server. They can be filtered, if necessary, by using a tool such as \fBsed\fR(1). .sp .LP More complicated examples can be built up when the user knows the format of requests required by the server. As another example, an email can be submitted to an SMTP server using: .sp .in +2 .nf $ nc localhost 25 << EOF HELO host.example.com MAIL FROM: > /etc/services wwwredir 8080/tcp # WWW redirect EOF # cat << EOF > /tmp/wwwredir.conf wwwredir stream tcp nowait nobody /usr/bin/nc /usr/bin/nc -w 3 realwww 80 EOF # inetconv -i /tmp/wwwredir.conf wwwredir -> /var/svc/manifest/network/wwwredir-tcp.xml Importing wwwredir-tcp.xml ...Done # inetadm -l wwwredir/tcp SCOPE NAME=VALUE name="wwwredir" endpoint_type="stream" proto="tcp" isrpc=FALSE wait=FALSE exec="/usr/bin/nc -w 3 realwww 80" arg0="/usr/bin/nc" user="nobody" default bind_addr="" default bind_fail_max=-1 default bind_fail_interval=-1 default max_con_rate=-1 default max_copies=-1 default con_rate_offline=-1 default failrate_cnt=40 default failrate_interval=60 default inherit_env=TRUE default tcp_trace=TRUE default tcp_wrappers=FALSE .fi .in -2 .sp .SS "Privileges" To bind to a privileged port number \fBnc\fR needs to be granted the \fBnet_privaddr\fR privilege. If Solaris Trusted Extensions are configured and the port \fBnc\fR should listen on is configured as a multi-level port \fBnc\fR also needs the \fBnet_bindmlp\fR privilege. .sp .LP Privileges can be assigned to the user or role directly, by specifying them in the account's default privilege set in \fBuser_attr\fR(5). However, this means that any application that this user or role starts have these additional privileges. To only grant the \fBprivileges\fR(7) when \fBnc\fR is invoked, the recommended approach is to create and assign an \fBrbac\fR(7) rights profile. See \fBEXAMPLES\fR for additional information. .SH EXAMPLES \fBExample 1 \fRUsing \fBnc\fR .sp .LP Open a TCP connection to port \fB42\fR of \fBhost.example.com\fR, using port \fB3141\fR as the source port, with a timeout of \fB5\fR seconds: .sp .in +2 .nf $ nc -p 3141 -w 5 host.example.com 42 .fi .in -2 .sp .sp .LP Open a UDP connection to port \fB53\fR of \fBhost.example.com\fR: .sp .in +2 .nf $ nc -u host.example.com 53 .fi .in -2 .sp .sp .LP Open a TCP connection to port 42 of \fBhost.example.com\fR using \fB10.1.2.3\fR as the IP for the local end of the connection: .sp .in +2 .nf $ nc -s 10.1.2.3 host.example.com 42 .fi .in -2 .sp .sp .LP Use a list of ports and port ranges for a port scan on various ports: .sp .in +2 .nf $ nc -z host.example.com 21-25,53,80,110-120,443 .fi .in -2 .sp .sp .LP Create and listen on a Unix Domain Socket: .sp .in +2 .nf $ nc -lU /var/tmp/dsocket .fi .in -2 .sp .sp .LP Create and listen on a UDP socket with associated port \fB8888\fR: .sp .in +2 .nf $ nc -u -l -p 8888 .fi .in -2 .sp .sp .LP which is the same as: .sp .in +2 .nf $ nc -u -l 8888 .fi .in -2 .sp .sp .LP Create and listen on a TCP socket with associated port \fB2222\fR and bind to address \fB127.0.0.1\fR only: .sp .in +2 .nf $ nc -l 127.0.0.1 2222 .fi .in -2 .sp .sp .LP Connect to port \fB42\fR of \fBhost.example.com\fR using an HTTP proxy at \fB10.2.3.4\fR, port \fB8080\fR. This example could also be used by \fBssh\fR(1). See the \fBProxyCommand\fR directive in \fBssh_config\fR(5) for more information. .sp .in +2 .nf $ nc -x10.2.3.4:8080 -Xconnect host.example.com 42 .fi .in -2 .sp .sp .LP The same example again, this time enabling proxy authentication with username \fBruser\fR if the proxy requires it: .sp .in +2 .nf $ nc -x10.2.3.4:8080 -Xconnect -Pruser host.example.com 42 .fi .in -2 .sp .sp .LP To run \fBnc\fR with the smallest possible set of privileges as a user or role that has additional privileges (such as the default \fBroot\fR account) it can be invoked using \fBppriv\fR(1) as well. For example, limiting it to only run with the privilege to bind to a privileged port: .sp .in +2 .nf $ ppriv -e -sA=basic,!file_link_any,!proc_exec,!proc_fork,\e !proc_info,!proc_session,net_privaddr nc -l 42 .fi .in -2 .sp .sp .LP To allow a user or role to use only \fBnc\fR with the \fBnet_privaddr\fR privilege, a rights profile needs to be created: .sp .in +2 .nf /etc/security/exec_attr Netcat privileged:solaris:cmd:::/usr/bin/nc:privs=net_privaddr /etc/security/prof_attr Netcat privileged:::Allow nc to bind to privileged ports:help=None.html .fi .in -2 .sp .sp .LP Assigning this rights profile using \fBuser_attr\fR(5) permits the user or role to run \fBnc\fR allowing it to listen on any port. To permit a user or role to use \fBnc\fR only to listen on specific ports a wrapper script should be specified in the rights profiles: .sp .in +2 .nf /etc/security/exec_attr Netcat restricted:solaris:cmd:::/usr/bin/nc-restricted:privs=net_privaddr /etc/security/prof_attr Netcat restricted:::Allow nc to bind to privileged ports:help=None.html .fi .in -2 .sp .sp .LP and write a shell script that restricts the permissible options, for example, one that permits one to bind only on ports between \fB42\fR and \fB64\fR (non-inclusive): .sp .in +2 .nf /usr/bin/nc-restricted: #!/bin/sh [ $# -eq 1 ] && [ $1 -gt 42 -a $1 -lt 64 ] && /usr/bin/nc -l -p "$1" .fi .in -2 .sp .sp .LP This grants the extra privileges when the user or role invokes \fBnc\fR using the wrapper script from a profile shell. See \fBpfsh\fR(1), \fBpfksh\fR(1), \fBpfcsh\fR(1), and \fBpfexec\fR(1). .sp .LP Invoking \fBnc\fR directly does not run it with the additional privileges, and neither does invoking the script without using \fBpfexec\fR or a profile shell. .SH ATTRIBUTES See \fBattributes\fR(7) for descriptions of the following attributes: .sp .sp .TS box; c | c l | l . ATTRIBUTE TYPE ATTRIBUTE VALUE _ Interface Stability See below. .TE .sp .LP The package name is Committed. The command line syntax is Committed for the \fB-4\fR, \fB-6\fR, \fB-l\fR, \fB-n\fR, \fB-p\fR, \fB-u\fR, and \fB-w\fR options and their arguments (if any). The \fIname\fR and \fIport\fR list arguments are Committed. The port range syntax is Uncommitted. The interface stability level for all other command line options and their arguments is Uncommitted. .SH SEE ALSO .BR cat (1), .BR pfcsh (1), .BR pfexec (1), .BR pfksh (1), .BR pfsh (1), .BR ppriv (1), .BR sed (1), .BR ssh (1), .BR telnet (1), .BR ssh_config (5), .BR user_attr (5), .BR attributes (7), .BR privileges (7), .BR rbac (7), .BR inetadm (8), .BR inetconv (8), .BR inetd (8) .SH AUTHORS The original implementation of \fBnc\fR was written by Hobbit, \fBhobbit@avian.org\fR. .sp .LP \fBnc\fR was rewritten with IPv6 support by Eric Jackson, \fBericj@monkey.org\fR. .SH NOTES UDP port scans always succeeds, that is, reports the port as open, rendering the \fB-uz\fR combination of flags relatively useless.