CVE-2022-4131: Denial of Service Vulnerability in GitLab CE/EE Due to Regex Issue in User Agent Parsing

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Introduction

A recently discovered issue in GitLab Community Edition (CE) and Enterprise Edition (EE) may lead to a potential Denial of Service (DoS) attack on your GitLab instance. The issue, identified as CVE-2022-4131, affects all versions of GitLab CE/EE starting from 10.8 up to and including 15.7.1. Let's dive into the details of the issue, understand the code snippets that cause the problem, and learn how the vulnerability can be exploited by an attacker.

Original References

1. GitLab Security Advisory
2. CVE-2022-4131 details on MITRE

Issue Details

The root cause of the issue lies within the way GitLab parses user agents. A specially crafted user agent string can trigger a regex issue, causing excessive CPU usage and ultimately leading to a Denial of Service condition. This condition can prevent users from effectively accessing or utilizing the GitLab instance, which could significantly disrupt operations.

Here's a simplified version of the affected code snippet

def user_agent_os
  os_regex = /(windows|macintosh|linux|android|iphone|ipad)/i
  match_data = request.user_agent.match(os_regex)
  match_data ? match_data.captures.first : 'Other'
end

In this code, the os_regex variable contains a regular expression to match user agent strings for common operating systems. However, the regex may encounter what is known as a "ReDoS" (Regular expression Denial of Service) when dealing with a specially crafted user agent string, causing lengthy matching times and substantially increasing CPU usage.

Exploit Details

An attacker looking to exploit this vulnerability would need to send specially crafted HTTP requests to *any* exposed GitLab instance, containing a user agent string designed to trigger the ReDoS in the affected code. A successful exploit would cause the GitLab instance to consume excessive CPU resources and ultimately be unable to respond to legitimate user requests, thereby impacting its availability.

Mitigation Steps

GitLab has released patches for the affected versions. To securely patch your GitLab instance, please update to the corresponding version below:

- For GitLab CE/EE 15.5.x, update to version 15.5.7 or later.
- For GitLab CE/EE 15.6.x, update to version 15.6.4 or later.
- For GitLab CE/EE 15.7.x, update to version 15.7.2 or later.

If updating to a patched version is not immediately possible, consider implementing network-level rate limiting or other protections to help limit the exposure and impact of this vulnerability.

Conclusion

CVE-2022-4131 is a critical security issue that allows an attacker to cause a Denial of Service condition on your GitLab instance. By understanding the code snippets involved, the underlying vulnerability, and the potential exploit, you can take appropriate actions to protect your environment. Update your GitLab instance to the latest security-patched version as soon as possible to minimize the risk of exploitation. Stay informed about security issues in your software stack to develop a proactive security posture.

Timeline

Published on: 01/12/2023 04:15:00 UTC
Last modified on: 01/18/2023 20:36:00 UTC