This cheat sheet provides various tips for
using Netcat on both Linux and Unix,
specifically tailored to the SANS 504, 517,
and 560 courses. All syntax is designed for
the original Netcat versions, released by
Hobbit and Weld Pond. The syntax here
can be adapted for other Netcats, including
ncat, gnu Netcat, and others.
$ nc [options] [TargetIPaddr] [port(s)]
The [TargetIPaddr] is simply the other sideโs IP
address or domain name. It is required in client mode
of course (because we have to tell the client where to
connect), and is optional in listen mode.
-l: Listen mode (default is client mode)
-L: Listen harder (supported only on Windows
version of Netcat). This option makes Netcat a
persistent listener which starts listening again
after a client disconnects
-u: UDP mode (default is TCP)
-p: Local port (In listen mode, this is port listened
on. In client mode, this is source port for all
packets sent)
-e: Program to execute after connection occurs,
connecting STDIN and STDOUT to the
program
-n: Donโt perform DNS lookups on names of
machines on the other side
-z: Zero-I/O mode (Donโt send any data, just emit
a packet without payload)
-wN: Timeout for connects, waits for N seconds
after closure of STDIN. A Netcat client or
listener with this option will wait for N seconds
to make a connection. If the connection
doesnโt happen in that time, Netcat stops
running.
-v: Be verbose, printing out messages on
Standard Error, such as when a connection
occurs
-vv: Be very verbose, printing even more details
on Standard Error
Netcat Relays on Windows
Netcat Command Flags
Purpose
Netcat
Cheat Sheet
By Ed Skoudis
POCKET REFERENCE GUIDE
http://www.sans.org
To start, enter a temporary directory where we will
create .bat files:
C:\> cd c:\temp
Listener-to-Client Relay:
C:\> echo nc [TargetIPaddr] [port] >
relay.bat
C:\> nc โl โp [LocalPort] โe relay.bat
Create a relay that sends packets from the local port
[LocalPort] to a Netcat Client connected to
[TargetIPaddr] on port [port]
Listener-to-Listener Relay:
C:\> echo nc โl โp [LocalPort_2] >
relay.bat
C:\> nc โl โp [LocalPort_1] โe
relay.bat
Create a relay that will send packets from any
connection on [LocalPort_1] to any connection
on [LocalPort_2]
Client-to-Client Relay:
C:\> echo nc [NextHopIPaddr] [port2] >
relay.bat
C:\> nc [PreviousHopIPaddr] [port] โe
relay.bat
Create a relay that will send packets from the
connection to [PreviousHopIPaddr] on port
[port] to a Netcat Client connected to
[NextHopIPaddr] on port [port2]
Fundamental Netcat Client:
$ nc [TargetIPaddr] [port]
Connect to an arbitrary port [port] at IP Address
[TargetIPaddr]
Fundamental Netcat Listener:
$ nc โl -p [LocalPort]
Create a Netcat listener on arbitrary local port
[LocalPort]
Both the client and listener take input from STDIN
and send data received from the network to STDOUT
Fundamentals
