Netcat (also known as ‘nc’) is a networking tool used for reading or writing from TCP and UDP sockets using an easy interface. It is designed as a dependable ‘back-end’ device that can be used directly or easily driven by other programs and scripts. Therefore, this tool is a treat to network administrators, programmers, and pen-testers as it’s a feature rich network debugging and investigation tool.

To open netcat simply go to your shell and enter ‘nc’:

#nc

Netcat command

Connecting to a host with Netcat

Use the -u option to start a TCP connection to a specified host and port:

#nc -u <host_ip> <port>

Connecting to a host with Netcat

Listen to inbound connections

You can set nc to listen on a port using -l option

#nc -l <port>

Listen to inbound connections with netcat

Scan ports with Netcat

This can easily be done using the ‘-z’ flag which instructs netcat not to initiate a connection but just check if the port is open. For example, In the following command we instruct netcat to check which ports are open between 80 and 100 on ‘localhost‘

#nc -z <host_ip> <port_range>

Scan ports with Netcat

Advanced port scan

To run an advanced port scan on a target, use the following command

#nc -v -n -z -w1 -r <target_ip>

Advanced port scan with netcat

This command will attempt to connect to random ports (-r) on the target ip running verbosely (-v) without resolving names (-n). without sending any data (-z) and waiting no more than 1 second for a connection to occur (-w1)

TCP banner grabbing With Netcat

You can grab the banner of any tcp service running on an ip address using nc:

#echo “” | nc -v -n -w1 <target_ip> <port_range>

TCP banner grabbing With Netcat

Transfer Files with Netcat

For this, you should have nc installed on both sending and receiving machines. First you have to start the nc in listener mode in receiving host

#nc -l <port> > file.txt

Transfer Files with Netcat

Now run the following command on the sending host:

#nc <target_ip> <port> --send-only < data.txt

In conclusion, Netcat comes with a lot of cool features that we can use to simplify our day-to-day tasks. Make sure to check out this article to learn some more interesting features in this tool.

 

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Ruwantha Nissanka

Ruwantha Nissanka is a Professional Cyber Security Engineer from Sri lanka with having a demonstrated history of providing cyber security services for multiple organizations in Sri Lanka. He is a positive person who wants to believe the best in others and he likes to help, encourage people and make them feel good.