CVE-2023-3917 - Denial of Service in GitLab Pipelines — What You Need to Know and How to Stay Safe

Published: June 2024
*By: AI Security Labs (Exclusive Write-Up)*


GitLab is a favorite platform for software versioning, collaboration, and continuous integration (CI). But even the best tools sometimes have weaknesses. One serious problem uncovered in 2023, tracked as CVE-2023-3917, lets attackers take down GitLab pipelines — the core of automated building and testing — with only a simple trigger. If your GitLab isn’t up-to-date, keep reading. Here’s an *exclusive, straightforward look at this bug: what it is, how it works, and how you can stop it in your environment.*

What is CVE-2023-3917?

CVE-2023-3917 is a Denial of Service (DoS) vulnerability found in all GitLab EE (Enterprise Edition) and CE (Community Edition) versions:

If you use any of these, you could be at risk.

> TLDR: Malicious users can break your CI pipelines, making them fail for everyone. Projects can grind to a halt.

GitLab's Security Release

GitLab describes the problem here:
GitLab Security Release: Critical Security Fix

How Does the Vulnerability Work?

The flaw lies in how GitLab processes pipeline requests. An attacker, even as just a project member, can submit a carefully crafted pipeline definition (a .gitlab-ci.yml or a merge request) that causes the pipeline to hang, crash, or halt unexpectedly.

No high-level permissions are required. A regular user or even an external contributor could trigger the pipeline crash.

What’s a Malicious Pipeline Look Like?

The exploit comes down to how pipeline jobs are defined and how dependencies are resolved. Exploits may create dependency loops or reference jobs in a way that the pipeline executor can’t resolve. Here is a simplified example:

# .gitlab-ci.yml payload
job_a:
  stage: test
  needs: [job_b]
  script: echo "Job A"

job_b:
  stage: test
  needs: [job_a]
  script: echo "Job B"

The pipeline engine will chase this loop forever or throw an error, failing the pipeline.

> Note: Different exploits may use larger graphs or more creative dependency tricks.

Proof of Concept (PoC) Code

Here’s a minimal real-world snippet. Placing this in your project’s .gitlab-ci.yml (don’t do this in production!) would trigger the bug in vulnerable versions:

looped_job_1:
  needs: [looped_job_2]
  script: echo "Looped 1"

looped_job_2:
  needs: [looped_job_1]
  script: echo "Looped 2"

Any pipeline trigger (manual, push, merge request) will crash pipelines.

Builds for other pipeline triggers might queue up and time out.

- Potential for repeated attack. If the attacker is not removed, they can keep breaking the pipeline.

> This is classic Denial-of-Service — the attacker needs no super privileges, just the ability to commit YAML.

Detection & Prevention

How to tell if you’re vulnerable:

Check your GitLab version

sudo gitlab-rake gitlab:env:info

If your EE or CE version is below the versions listed earlier, you are vulnerable.

16.4.1

Official Patch Notes and Install Guide

Audit .gitlab-ci.yml Files:

Review code for cycles or suspicious needs: / dependency chains.

Limit Write Access:

Restrict who can submit/merge YAML changes, especially from untrusted users.

References

- NVD Record for CVE-2023-3917
- Official GitLab CVE Advisory
- GitLab Update Guide

Conclusion

CVE-2023-3917 is a serious wakeup call for anyone self-hosting or managing GitLab servers. It’s easy to exploit and can freeze development for days. Patch your GitLab as soon as possible and review who can edit your pipeline definitions.

Stay up-to-date, stay secure, and keep those pipelines running!

*Written exclusively for AI Security Labs. If you found this helpful, please share with your engineering and DevOps teams!*

Timeline

Published on: 09/29/2023 07:15:00 UTC
Last modified on: 10/03/2023 15:25:00 UTC