CVE-2023-5226 in GitLab
Summary
by MITRE • 12/01/2023
An issue has been discovered in GitLab affecting all versions before 16.4.3, all versions starting from 16.5 before 16.5.3, all versions starting from 16.6 before 16.6.1. Under certain circumstances, a malicious actor bypass prohibited branch checks using a specially crafted branch name to manipulate repository content in the UI.
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Analysis
by VulDB Data Team • 11/20/2025
This vulnerability in GitLab represents a significant access control bypass that undermines the platform's repository protection mechanisms. The issue stems from insufficient validation of branch names during repository operations, allowing malicious actors to craft specific branch names that circumvent the intended branch protection rules. The vulnerability affects multiple version streams including 16.4.x before 16.4.3, 16.5.x before 16.5.3, and 16.6.x before 16.6.1, indicating a widespread impact across the GitLab release cycle. The flaw operates through a specific manipulation technique where attackers can exploit the branch name parsing logic to gain unauthorized access to protected repository content through the web user interface.
The technical implementation of this vulnerability involves the manipulation of branch naming conventions to exploit gaps in the validation process. When GitLab processes repository operations, it typically enforces branch protection rules to prevent unauthorized modifications to critical branches such as main, develop, or release branches. However, the vulnerability allows attackers to create branch names that contain special characters or sequences that bypass these validation checks. This manipulation enables unauthorized users to push changes to protected branches, effectively circumventing the access control mechanisms that should prevent such modifications. The vulnerability specifically targets the UI layer where users interact with repository content, making it particularly dangerous as it can be exploited through normal user interface operations without requiring advanced technical knowledge or direct system access.
The operational impact of this vulnerability extends beyond simple unauthorized access to include potential data integrity compromise and security policy violations. Attackers can exploit this weakness to modify critical code repositories, potentially introducing malicious code or destructive changes that could affect entire development pipelines. The vulnerability's presence in the UI layer means that it could be exploited by users with legitimate access rights who wish to escalate their privileges or by external attackers who gain access to compromised accounts. This represents a significant risk to organizations that rely on GitLab for source code management, as it undermines the fundamental security assumptions of branch protection mechanisms. The vulnerability also impacts audit trails and compliance requirements, as unauthorized modifications may not be properly logged or detected by existing monitoring systems.
Organizations should immediately upgrade to GitLab versions 16.4.3, 16.5.3, or 16.6.1 to remediate this vulnerability, as these releases contain the necessary patches to address the branch name validation issue. System administrators should conduct comprehensive audits of repository access controls and monitor for any suspicious activities that may have occurred during the vulnerable period. Additional mitigations include implementing stricter branch naming policies, enhancing monitoring of repository modifications, and conducting regular security assessments of GitLab configurations. The vulnerability aligns with CWE-284 Access Control Bypass and maps to ATT&CK technique T1078 Valid Accounts, as it allows unauthorized access to protected repository content through manipulated branch names. Organizations should also consider implementing additional security controls such as two-factor authentication for repository access and automated scanning for suspicious branch name patterns to prevent exploitation of similar vulnerabilities in the future.