CVE-2020-13348 in Enterprise Edition
Summary
by MITRE • 11/18/2020
An issue has been discovered in GitLab EE affecting all versions starting from 10.2. Required CODEOWNERS approval could be bypassed by targeting a branch without the CODEOWNERS file. Affected versions are >=10.2, =13.4, =13.5,
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Analysis
by VulDB Data Team • 12/08/2020
This vulnerability in GitLab Enterprise Edition represents a significant access control flaw that undermines the code review governance mechanisms designed to protect software development integrity. The issue specifically targets the CODEOWNERS functionality which is intended to enforce mandatory approval requirements for changes to specific code paths. When developers create branches that lack CODEOWNERS files, the system fails to properly validate whether required approvals exist, creating an exploitable gap in the security controls. This bypass mechanism allows malicious actors or unauthorized developers to circumvent the intended review processes that should ensure code quality and security compliance before merging changes into protected branches.
The technical implementation of this vulnerability stems from how GitLab processes branch-level access controls when CODEOWNERS files are absent or improperly configured. The system should consistently enforce approval requirements regardless of branch structure or file presence, but instead exhibits inconsistent behavior where branches without CODEOWNERS files can bypass the required approval workflows. This flaw operates at the intersection of access control and configuration management, where the absence of expected files creates an unexpected validation path that does not properly enforce security policies. The vulnerability manifests when the system fails to properly validate the existence of required CODEOWNERS entries in the target branch, allowing changes to proceed without the necessary approval signatures.
The operational impact of this vulnerability extends beyond simple bypass capabilities to represent a fundamental weakness in GitLab's code governance framework. Organizations relying on CODEOWNERS for security policy enforcement may experience unauthorized code changes that could introduce vulnerabilities, backdoors, or other security issues without proper review. This vulnerability particularly affects organizations with strict compliance requirements where code review processes are mandatory for specific code areas, potentially leading to audit failures or regulatory violations. The risk is amplified in environments where sensitive code paths lack proper oversight, as attackers could exploit this bypass to introduce malicious changes that would otherwise require multiple approvals.
Organizations should implement immediate mitigations including comprehensive code review policy enforcement, regular audit of CODEOWNERS file configurations, and enhanced monitoring of branch creation and modification activities. The vulnerability aligns with CWE-284 Access Control Issues, specifically addressing improper access control mechanisms that allow unauthorized users to bypass security controls. From an ATT&CK framework perspective, this represents a privilege escalation technique that leverages configuration weaknesses to bypass mandatory access controls. Recommended remediation includes upgrading to patched versions of GitLab, implementing additional validation checks for branch configurations, and establishing automated monitoring systems that can detect and alert on potential CODEOWNERS bypass attempts. Security teams should also consider implementing additional layers of code review enforcement beyond the built-in CODEOWNERS functionality to ensure comprehensive protection against similar configuration-based bypass vulnerabilities.