Overview
CVE-2025-12983 is a low-severity denial-of-service (DoS) vulnerability affecting GitLab Community Edition (CE) and Enterprise Edition (EE). This vulnerability exists in versions prior to 18.3.6, 18.4.4, and 18.5.2. It allows an authenticated attacker to potentially crash a GitLab instance by submitting maliciously crafted markdown content containing excessively nested formatting patterns. While the impact is considered low due to the requirement of authentication and the relatively contained nature of the denial of service, it’s still important to address to maintain the stability and availability of your GitLab environment.
Technical Details
The vulnerability stems from improper handling of markdown rendering when processing nested formatting elements. Specifically, excessive nesting of elements like bold, italics, or lists can lead to resource exhaustion during the rendering process. An authenticated attacker can exploit this by submitting markdown content with a large number of nested formatting patterns to GitLab through various channels, such as issues, comments, merge request descriptions, and wiki pages.
The issue has been identified and addressed by GitLab developers, and patches have been released to mitigate this vulnerability.
CVSS Analysis
The Common Vulnerability Scoring System (CVSS) provides a standardized way to assess the severity of vulnerabilities. For CVE-2025-12983, the CVSS score is 3.5, indicating a Low severity.
- CVSS Score: 3.5
- Vector String: (This would be provided in a full CVSS analysis)
- Rationale: The low score is attributed to the requirement for authentication and the limited scope of the denial of service. While an attacker can potentially disrupt service, it is unlikely to lead to data loss or unauthorized access.
Possible Impact
While the severity is low, the vulnerability can still have a negative impact:
- Denial of Service: The primary impact is a denial of service, potentially making GitLab unavailable to users.
- Temporary Instability: The vulnerability can cause temporary instability and performance degradation as the GitLab instance attempts to render the malicious markdown.
- User Frustration: If the vulnerability is actively exploited, users may experience frustration due to GitLab downtime.
Mitigation and Patch Steps
The recommended mitigation is to upgrade your GitLab instance to one of the following versions or later:
- 18.3.6
- 18.4.4
- 18.5.2
Steps to Upgrade:
- Backup your GitLab instance: Before upgrading, always create a backup to prevent data loss.
- Follow the official GitLab upgrade guide: Refer to the GitLab documentation for detailed upgrade instructions specific to your installation.
- Test the upgraded instance: After the upgrade, thoroughly test the GitLab instance to ensure everything is working correctly.
If you are unable to upgrade immediately, consider implementing input validation and sanitization on user-submitted markdown content as a temporary workaround (although upgrading is highly recommended). However, be aware that this can be complex and may not be completely effective against all possible variations of the exploit.
