CVE-2026-1751: GitLab Auth Bypass Vulnerability

CVE-2026-1751 Overview

A vulnerability has been discovered in GitLab CE/EE affecting all versions starting with 16.8 before 18.5.0 that could have allowed unauthorized edits to merge request approval rules under certain conditions. This authorization bypass vulnerability (CWE-862: Missing Authorization) enables attackers to potentially manipulate merge request workflows without proper access controls.

Critical Impact

Unauthorized modification of merge request approval rules could allow attackers to bypass code review requirements and push malicious code into protected branches.

Affected Products

• GitLab Community Edition (CE) versions 16.8 to before 18.5.0
• GitLab Enterprise Edition (EE) versions 16.8 to before 18.5.0

Discovery Timeline

• 2026-02-02 - CVE-2026-1751 published to NVD
• 2026-02-04 - Last updated in NVD database

Technical Details for CVE-2026-1751

Vulnerability Analysis

This vulnerability stems from a missing authorization check (CWE-862) in GitLab's merge request approval rules functionality. When certain conditions are met, an attacker with network access can modify approval rules that govern the merge request workflow, potentially circumventing security controls designed to ensure code review and approval before merging.

The attack requires user interaction and is considered high complexity to exploit, meaning specific conditions must be present for successful exploitation. While the integrity impact is limited, the vulnerability could undermine the trust and security guarantees that merge request approval workflows provide in development environments.

Root Cause

The root cause is a missing authorization check in the code path that handles edits to merge request approval rules. Under specific conditions, the application fails to properly verify that the user making the request has sufficient permissions to modify approval rule configurations. This represents a classic broken access control vulnerability where authorization enforcement is incomplete.

Attack Vector

The vulnerability is exploitable over the network and requires user interaction. An attacker would need to craft malicious requests targeting the approval rules functionality while certain application state conditions are present. The attack flow involves:

1. Identifying a GitLab instance running a vulnerable version (16.8 to before 18.5.0)
2. Crafting requests to modify merge request approval rules
3. Exploiting the missing authorization check under the required conditions
4. Successfully modifying approval rules without proper authorization

The vulnerability mechanism involves exploiting the missing authorization check in GitLab's merge request approval rules handling. For technical details, refer to the HackerOne Report #2980839 and the GitLab Issue #519340.

Detection Methods for CVE-2026-1751

Indicators of Compromise

• Unexpected modifications to merge request approval rules in project settings
• Audit logs showing approval rule changes by users without appropriate permissions
• Merge requests being approved or merged with fewer approvals than configured policies require

Detection Strategies

• Review GitLab audit logs for unauthorized modifications to approval rules
• Monitor for unusual API requests targeting merge request approval endpoints
• Implement alerts for changes to protected branch and approval rule configurations

Monitoring Recommendations

• Enable comprehensive audit logging for all merge request and approval rule activities
• Configure alerts for any approval rule modifications outside of normal administrative workflows
• Regularly review merge request approval configurations for unauthorized changes
• Monitor for patterns of merge requests bypassing normal approval requirements

How to Mitigate CVE-2026-1751

Immediate Actions Required

• Upgrade GitLab CE/EE to version 18.5.0 or later
• Review audit logs for any unauthorized approval rule modifications
• Verify current merge request approval rules match intended security policies
• Consider temporarily restricting access to approval rule configuration while patching

Patch Information

GitLab has addressed this vulnerability in version 18.5.0. Organizations should upgrade to this version or later to remediate the vulnerability. Patch information and upgrade guidance can be found in the GitLab Issue #519340.

Workarounds

• Restrict access to merge request approval rule settings to trusted administrators only
• Implement additional monitoring on approval rule changes via external audit tools
• Review and validate approval rules regularly to detect unauthorized modifications
• Enable protected branches with strict merge requirements as an additional layer of security

# Configuration example - Verify GitLab version
gitlab-rake gitlab:env:info | grep "GitLab"

# Check current approval rules via GitLab Rails console
gitlab-rails runner "Project.all.each { |p| puts \"#{p.name}: #{p.approval_rules.count} rules\" }"