CVE-2026-14288: 
GitLab 脆弱性分析と緩和策

CVE-2026-14288 is an authorization bypass vulnerability in GitLab Enterprise Edition (EE) that allows authenticated users to bypass required merge request approval policies on protected branches due to improper access control during approval rule synchronization. It affects all GitLab EE versions from 17.4 before 19.3.6, 19.4 before 19.4.3, and 19.5 before 19.5.1. The vulnerability was published on October 22, 2026, and has been remediated by GitLab. It carries a CVSS v3.1 base score of 3.1 (Low) (EUVD, GitLab Patch Release).

The root cause is classified as CWE-706 (Use of Incorrectly-Resolved Name or Reference), manifesting as improper access control during approval rule synchronization in GitLab EE. Under certain conditions, the synchronization process fails to correctly enforce approval policy references on protected branches, allowing an authenticated user with at least developer-level permissions to merge code without obtaining the required approvals. The attack vector is network-based, requires low privileges, no user interaction, and has high attack complexity, meaning specific conditions must be met for exploitation to succeed (EUVD, GitLab Patch Release). No public proof-of-concept code has been identified.

Successful exploitation allows an authenticated user (e.g., a developer or maintainer) to merge code into protected branches without satisfying mandatory approval requirements, undermining code review and change management controls. This primarily affects integrity — unauthorized or malicious code changes could be introduced into production-bound branches without proper oversight. There is no confidentiality or availability impact, and lateral movement potential is limited, but the risk of supply chain compromise or introduction of malicious code is a meaningful concern in enterprise environments (EUVD).

There is no evidence of active in-the-wild exploitation or a publicly available proof-of-concept as of the time of reporting (EUVD). The EPSS score is approximately 0.0024 (0.24%), indicating a low probability of exploitation in the near term. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. Exploitation requires an authenticated account with at least developer permissions and specific conditions to be met, further limiting practical exploitability (EUVD, GitLab Patch Release).

1. Reconnaissance: Identify a GitLab EE instance running a vulnerable version (17.4 through 19.3.5, 19.4.0–19.4.2, or 19.5.0) with protected branches and mandatory merge request approval policies configured.
2. Authenticate: Log in with a valid account that has at least developer-level permissions on the target project.
3. Trigger approval rule synchronization: Perform actions that trigger the approval rule synchronization process under the specific conditions that cause the access control check to fail (exact conditions are not publicly documented).
4. Submit merge request: Open a merge request targeting a protected branch that normally requires one or more approvals.
5. Bypass approval policy: Due to the improper reference resolution during synchronization, the required approval rules are not correctly enforced, allowing the merge request to be merged without obtaining the required approvals (EUVD).

• Logs: GitLab audit logs showing merge requests merged on protected branches with fewer approvals than the configured policy requires; approval rule synchronization events immediately preceding unexpected merges.
• Application Activity: Merge requests on protected branches that show zero or insufficient approvals in the merge request history but were successfully merged.
• Configuration Changes: Unexpected or unexplained changes to approval rules on protected branches around the time of suspicious merges.

GitLab has released patched versions: 19.3.6, 19.4.3, and 19.5.1. All GitLab EE users running affected versions (17.4 through 19.3.5, 19.4.0–19.4.2, or 19.5.0) should upgrade immediately. If immediate patching is not possible, administrators should review and audit merge request approval policies on protected branches, monitor for suspicious approval rule changes or unexpected merge activity, and restrict approval rule modification permissions to the minimum necessary set of users (GitLab Patch Release, EUVD).

The vulnerability was covered by several security news outlets as part of broader GitLab patch release coverage, including Heise and CyberSecurityNews, though coverage was primarily focused on a more critical RCE vulnerability (CVE-2026-110264) patched in the same release cycle (Heise). Community discussion on Mastodon/infosec.exchange noted the patch release. No significant independent researcher commentary specific to CVE-2026-14288 has been identified.