CVE-2025-9957: GitLab Authorization Bypass Vulnerability

CVE-2025-9957 Overview

An authorization bypass vulnerability has been identified in GitLab Community Edition (CE) and Enterprise Edition (EE) that allows authenticated users with project owner permissions to bypass group fork prevention settings. This improper authorization flaw affects all GitLab versions from 11.2 through 18.9.6, 18.10 before 18.10.4, and 18.11 before 18.11.1.

The vulnerability stems from insufficient authorization checks when processing fork operations, enabling project owners to circumvent security controls that should prevent forking at the group level.

Critical Impact

Project owners can bypass organizational security policies designed to prevent unauthorized code duplication, potentially leading to intellectual property leakage or circumvention of compliance controls.

Affected Products

• GitLab Community Edition (CE) versions 11.2 to 18.9.5
• GitLab Enterprise Edition (EE) versions 11.2 to 18.9.5
• GitLab CE/EE versions 18.10.0 to 18.10.3 and version 18.11.0

Discovery Timeline

• 2026-04-22 - CVE-2025-9957 published to NVD
• 2026-04-22 - GitLab releases security patch (versions 18.9.6, 18.10.4, 18.11.1)
• 2026-04-23 - Last updated in NVD database

Technical Details for CVE-2025-9957

Vulnerability Analysis

This vulnerability is classified as CWE-863 (Incorrect Authorization), indicating that the application does not properly verify whether a user has permission to perform a specific action. In this case, GitLab fails to adequately enforce group-level fork prevention policies when a user with project owner permissions initiates a fork operation.

The flaw allows authenticated attackers with elevated project privileges to perform actions that should be restricted by group-level administrative controls. While the attack requires high-level privileges (project owner), the network-accessible nature of GitLab instances means this can be exploited remotely without user interaction.

Root Cause

The root cause lies in improper authorization logic within GitLab's fork handling mechanism. When processing fork requests from project owners, the authorization layer does not correctly evaluate group-level restrictions that administrators have configured to prevent forking. This results in a privilege gap where project-level permissions can override group-level security policies.

The authorization check fails to validate the hierarchical permission model, where group settings should take precedence over individual project owner actions for security-critical operations like forking.

Attack Vector

The attack is network-based and requires an authenticated attacker with project owner permissions within the target GitLab instance. The exploitation path involves:

1. An attacker authenticates to the GitLab instance with valid credentials
2. The attacker must have project owner role within a project that belongs to a group with fork prevention enabled
3. The attacker initiates a fork operation through the GitLab interface or API
4. Due to improper authorization checks, the fork operation succeeds despite group-level restrictions

The vulnerability affects the integrity of repository access controls, though confidentiality and availability impacts are limited based on the nature of the flaw.

Detection Methods for CVE-2025-9957

Indicators of Compromise

• Unexpected fork operations appearing in GitLab audit logs for projects within groups that have fork prevention enabled
• Repository forks created by project owners in groups where forking should be administratively disabled
• Anomalous project creation events that correlate with fork activities in restricted groups

Detection Strategies

• Review GitLab audit logs for fork operations, filtering for projects belonging to groups with prevent_forking settings enabled
• Monitor API calls to fork endpoints (/api/v4/projects/:id/fork) from users with project owner roles in restricted groups
• Implement alerting on repository creation events that reference parent projects in fork-restricted groups
• Cross-reference group configuration settings with actual fork activity to identify policy violations

Monitoring Recommendations

• Enable comprehensive GitLab audit logging and ensure retention policies cover the period since initial deployment of vulnerable versions
• Configure SIEM rules to correlate fork operations with group permission settings
• Establish baseline metrics for fork operations and alert on deviations, particularly in groups with security-sensitive repositories

How to Mitigate CVE-2025-9957

Immediate Actions Required

• Upgrade GitLab CE/EE to version 18.9.6, 18.10.4, or 18.11.1 immediately
• Audit existing repositories for unauthorized forks created since deployment of affected versions
• Review group-level fork prevention settings and verify they are correctly configured
• Temporarily restrict project owner permissions in sensitive groups until patching is complete

Patch Information

GitLab has released patched versions addressing this vulnerability. Organizations should upgrade to the following versions based on their current deployment:

Detailed patch information is available in the GitLab Patch Release Announcement.

Additional technical details can be found in the HackerOne Vulnerability Report and GitLab Work Item Details.

Workarounds

• Implement additional access controls at the network layer to restrict GitLab API access to trusted networks only
• Temporarily demote project owners to maintainer roles in groups with fork prevention requirements until patching is complete
• Configure GitLab instance-level settings to disable forking globally as an interim measure for highly sensitive deployments
• Enable additional logging and monitoring for fork-related activities to detect potential exploitation attempts