Security in development tools is often overlooked until something goes wrong. On June 2025, a new GitLab vulnerability was disclosed as CVE-2025-10868—and though it doesn’t seem like a traditional “remote code execution” bug, it can still seriously affect servers. Here’s what you need to know about this GitLab flaw, practical exploit details, and how to defend your systems.

What is CVE-2025-10868?

This vulnerability was discovered in GitLab Community Edition (CE) and Enterprise Edition (EE), specifically affecting:

Version 18.4 *before* 18.4.1

The weakness lies in certain string conversion methods in the codebase. When these methods receive a very large string as input, they don’t handle them efficiently, causing performance to tank. Think “resource exhaustion” or “DoS-by-slowness,” not just outright server crash.

Why Should You Care?

If your GitLab server lets users input or process long strings (think of user profiles, issue trackers, merge requests, or custom fields), it can be choked by attackers—even inadvertently—by submitting super-long strings. This can freeze web operations, delay legitimate requests, and in worst cases, starve the server’s resources.

This issue is a *Denial of Service (DoS)* risk, where an attacker can essentially tie up your GitLab instance just by making it chew through “bad” input.

Digging Into the Code

While original GitLab code is complex, here’s a simple example. Consider a method somewhere in GitLab dealing with string conversion:

# Example Ruby method resembling the vulnerable code pattern
def to_certain_format(input)
  # Inefficient processing on giant strings
  formatted = input.gsub(/./) { |c| expensive_conversion(c) }
  return formatted
end

def expensive_conversion(char)
  # Simulating a slow operation (e.g. complex unicode transformation)
  sleep(.001)
  char.upcase
end

If input is 10,000,000 characters, this could consume _hours_ of CPU time due to the sleep in every character conversion.

In real GitLab code, string methods like gsub, encoding conversions, or unsafe manipulation might trigger this problem. Just one endpoint handling user content and calling such methods could freeze a worker.

Attack Scenario

1. Find a User Input Endpoint: Find anywhere on GitLab where you can submit (even as an authenticated user) a large string. For example, an issue description, commit message, or profile bio.
2. Submit Massive Payload: Paste a large (e.g. 10MB+) string with content that triggers string conversion.
3. Wait: The server will process this slowly, possibly holding up one or more threads/processes, and hogging CPU.

Repeat: Multiple requests compound the problem—now you’re denying service to others.

Exploit Example using curl

(for demonstration only—do not attack unauthorized servers!)

# Substitute <gitlab-url> and <token> with your instance and credentials
BIG_STR=$(head -c 10000000 </dev/urandom | base64)
curl -X POST "https://<gitlab-url>/api/v4/issues"; \
  -H "PRIVATE-TOKEN: <token>" \
  -d "title=Test&description=$BIG_STR"

Official References

- GitLab’s release post on the fix
- NVD CVE-2025-10868 entry

Conclusion: Take Action, Even on “DoS-Only” Bugs

While CVE-2025-10868 doesn’t allow attackers to steal information or run code, it’s a classic example of how unguarded performance drains can bring even robust software like GitLab to its knees. Quick upgrades and vigilance are your best defense. Don’t wait for a real incident—patch now.

*For more exclusive, easy-to-read deep-dives on developer security issues, keep following us!*

References

- Official GitLab Security Release 2025-06-10
- CVE-2025-10868 on NVD Database

Timeline

Published on: 09/26/2025 10:15:46 UTC
Last modified on: 09/29/2025 13:11:31 UTC