In late 2022, the GitLab team patched a serious issue – CVE-2022-3818 – which highlights just how dangerous seemingly simple bugs can be. This vulnerability is all about how GitLab parsed URLs, but with the right attack, an adversary could bring your server to its knees. In this article, we'll break down what CVE-2022-3818 is, how it could be exploited, show a simple proof-of-concept, and help you secure your instance.

1. What Is CVE-2022-3818?

CVE-2022-3818 is an uncontrolled resource consumption flaw in how GitLab parsed URLs supplied to it. The issue affected:

- GitLab CE/EE versions prior to 15.3.5

15.5 series prior to 15.5.2

When a user (or attacker) gave GitLab a specially crafted URL, the backend code would enter a loop or perform a heavy computation, resulting in excessive CPU or memory use. If abused repeatedly, this could tank server performance or even cause a full Denial of Service (DoS).

References

- Original GitLab Advisory
- CVE Record on NIST
- HackerOne disclosure (summary)

2. The Root Problem: Infinite URL Processing

It all boiled down to the way GitLab's Ruby code parsed URLs. GitLab uses a lot of automated processes that take in user-supplied URLs (like for repository mirroring, or webhooks). When these URLs were parsed, certain patterns or lengths could cause the parser to work overtime.

A common attack pattern is a URL with a huge number of slashes (/) or using structures that would make the parser enter a near-infinite loop or recursion.

Here's a simplified Ruby code that demonstrates a similar uncontrolled resource consumption bug

require 'uri'

# A malicious URL designed to cause excessive parsing
long_url = "http://"; + "a" * 100000 + "/"

# Vulnerable URL parsing (hypothetical, similar to pre-patch behavior)
begin
  parsed_url = URI.parse(long_url)
  puts parsed_url
rescue => e
  puts "Error during parsing: #{e}"
end

If URI.parse (or GitLab's actual internal parser) doesn't protect against huge inputs, this will eat a lot of RAM and CPU. Attackers would send thousands of such requests, basically turning your GitLab into a smoke machine!

In reality, attackers would submit these URLs through any functionality that accepts a user-provided repository URL (e.g., "Import repository", mirror configuration, webhook endpoint, etc.).

potentially open the door for further attacks while admins try to recover.

This is especially risky for self-hosted GitLab instances that expose repository import or webhook features to the public internet.

Example HTTP Request (webhook endpoint)

POST /api/v4/projects/:id/hooks
Content-Type: application/json

{
  "url": "http://aaaaaaaaa...aaaaa/";,  // 'a' repeated 100,000 times
  "enable_ssl_verification": false
}

If the backend tries to process this, resources spike.

Upgrade immediately to at least one of the fixed versions (15.3.5+, 15.4.4+, 15.5.2+).

- Limit public features: For externally accessible GitLab, restrict who can import repos or add webhooks.

Monitor server load and anomalous user activity.

- Apply security updates promptly!

6. Quick FAQ

Q: Could this be used to hack or takeover GitLab?  
A: No known code execution, but a skilled attacker could combine this DoS with other exposed flaws for more damage.

Q: How can I check if I’m vulnerable?  
A: Run gitlab-rake gitlab:env:info to check your version. If it’s earlier than the fixed releases, you need to update!

Q: Is this only on public GitLab servers?  
A: No, private/self-hosted instances are at risk too—especially if you allow open registration or untrusted users.

7. Conclusion

CVE-2022-3818 is a classic example where a tiny mistake in input handling can turn into a major security headache. If you manage a GitLab server, check your version and upgrade now. And always remember: never trust user input – even if it's "just a URL"!

Further Reading

- GitLab 15.5.2 Release Announcement
- Mitre CVE Entry
- Secure URL Input Handling in Ruby

Timeline

Published on: 11/10/2022 00:15:00 UTC
Last modified on: 11/11/2022 00:49:00 UTC