CVE-2025-3396: GitLab Auth Bypass Vulnerability

CVE-2025-3396 Overview

A security vulnerability has been discovered in GitLab Enterprise Edition (EE) that allows authenticated project owners to bypass group-level forking restrictions through manipulated API requests. This authorization bypass vulnerability (CWE-863) affects all GitLab EE versions from 13.3 through multiple release branches, potentially undermining organizational security policies designed to control code distribution and intellectual property management.

Critical Impact

Authenticated project owners can circumvent administrative forking controls, potentially leading to unauthorized code distribution and violation of organizational security policies.

Affected Products

• GitLab Enterprise Edition versions 13.3 before 17.11.6
• GitLab Enterprise Edition versions 18.0 before 18.0.4
• GitLab Enterprise Edition versions 18.1 before 18.1.2

Discovery Timeline

• 2025-07-10 - CVE-2025-3396 published to NVD
• 2025-07-25 - Last updated in NVD database

Technical Details for CVE-2025-3396

Vulnerability Analysis

This vulnerability represents an Improper Authorization flaw (CWE-863) within GitLab EE's forking permission system. The issue stems from inadequate validation of API requests when project owners attempt to fork repositories. While the GitLab web interface properly enforces group-level forking restrictions configured by administrators, the API endpoint responsible for handling fork operations fails to implement equivalent authorization checks.

The vulnerability allows authenticated users with project owner privileges to craft specific API requests that circumvent the intended group-level restrictions. This means that even when administrators have explicitly disabled forking at the group level to protect sensitive codebases, project owners can still create unauthorized forks by directly interacting with the vulnerable API endpoint.

Root Cause

The root cause lies in inconsistent authorization enforcement between GitLab's web interface and its API layer. The group-level forking restriction logic was properly implemented in the UI flow but was not adequately mirrored in the corresponding API endpoint handlers. This authorization gap allowed authenticated project owners to invoke forking functionality through direct API calls, bypassing the restriction checks that would normally prevent such actions through the standard interface.

Attack Vector

The attack is network-based and requires authenticated access with project owner privileges. An attacker would need to:

1. Authenticate to the GitLab EE instance with valid credentials
2. Hold project owner permissions on the target repository
3. Craft an API request to the forking endpoint that bypasses the group-level restriction validation
4. Successfully create a fork despite administrative policies prohibiting such action

The vulnerability exploits the trust boundary between the UI authorization layer and the API authorization layer. By directly calling the API endpoint and manipulating request parameters, an attacker can instruct GitLab to perform a fork operation without triggering the group-level permission checks. For technical implementation details, refer to GitLab Issue #534636 and HackerOne Report #3079956.

Detection Methods for CVE-2025-3396

Indicators of Compromise

• Unexpected fork creation events in repositories where group-level forking is disabled
• API access logs showing fork requests from project owners in restricted groups
• Audit logs indicating fork operations that bypass normal UI workflows
• New repositories appearing as forks of restricted projects without corresponding UI activity

Detection Strategies

• Monitor GitLab audit logs for fork creation events, particularly those originating from API requests rather than UI interactions
• Implement alerts for fork operations in groups where forking restrictions are enabled
• Review API access patterns for authenticated users with project owner privileges
• Cross-reference fork creation timestamps with UI session activity to identify API-only operations

Monitoring Recommendations

• Enable comprehensive audit logging in GitLab EE for all repository operations
• Configure SIEM alerts for anomalous fork patterns in restricted groups
• Regularly review fork activity reports for projects containing sensitive code
• Implement periodic access control audits comparing configured restrictions against actual repository structures

How to Mitigate CVE-2025-3396

Immediate Actions Required

• Upgrade GitLab EE to patched versions: 17.11.6, 18.0.4, or 18.1.2 depending on your release branch
• Audit existing forks to identify any unauthorized duplications created during the vulnerability window
• Review API access logs for suspicious fork operations against restricted repositories
• Temporarily restrict API access for project owners if immediate patching is not possible

Patch Information

GitLab has released security patches addressing this authorization bypass vulnerability. Organizations should upgrade to the following fixed versions:

• Version 17.11.6 for the 17.11.x branch
• Version 18.0.4 for the 18.0.x branch
• Version 18.1.2 for the 18.1.x branch

Detailed patch information and upgrade instructions are available through GitLab Issue #534636.

Workarounds

• Implement network-level API access controls to restrict fork API endpoints to trusted sources
• Use GitLab's IP allowlist feature to limit API access from authorized networks only
• Temporarily revoke project owner privileges from users in highly sensitive groups until patching is complete
• Deploy a reverse proxy rule to block or log fork-related API requests for manual review