CVE-2021-39931 in Community Edition
Summary
by MITRE • 12/13/2021
An issue has been discovered in GitLab CE/EE affecting all versions starting from 8.11 before 14.3.6, all versions starting from 14.4 before 14.4.4, all versions starting from 14.5 before 14.5.2. Under specific condition an unauthorised project member was allowed to delete a protected branches due to a business logic error.
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Analysis
by VulDB Data Team • 12/16/2021
The vulnerability CVE-2021-39931 represents a critical business logic flaw in GitLab Community Edition and Enterprise Edition platforms that persisted across multiple version ranges. This issue specifically targeted the branch protection mechanisms within GitLab's access control system, creating a scenario where unauthorized users could exploit a gap in the permission model to delete protected branches. The vulnerability affected versions from 8.11 through 14.3.5, 14.4 through 14.4.3, and 14.5 through 14.5.1, indicating a long-standing flaw that remained undetected for several major releases. The root cause stemmed from inadequate validation of user permissions during branch deletion operations, allowing members with restricted access levels to bypass normal protection protocols.
The technical implementation of this vulnerability exploited the gap between the intended access control model and the actual execution of branch protection logic. When a user attempted to delete a branch that was marked as protected, the system failed to properly verify whether the requesting user possessed the necessary administrative privileges required for such destructive operations. This business logic error occurred specifically under certain conditional circumstances that were not properly accounted for in the authorization checks, creating an unexpected path for privilege escalation. The flaw did not involve traditional authentication bypasses or injection attacks but rather represented a fundamental misalignment in how the system evaluated user permissions for critical operations.
The operational impact of this vulnerability extends beyond simple unauthorized deletions, as protected branches often contain critical code that should remain immutable to maintain system integrity and security posture. An attacker with access to a project could potentially compromise the entire development workflow by removing branches that were specifically protected to prevent accidental or malicious modifications. This vulnerability particularly affected organizations that relied on GitLab's branch protection features as part of their security controls, creating a scenario where the very mechanisms designed to protect code repositories could be circumvented. The implications were especially severe in environments where protected branches contained sensitive code, release candidates, or security-critical implementations.
Organizations affected by this vulnerability should immediately implement the patches provided by GitLab for versions 14.3.6, 14.4.4, and 14.5.2, as these releases contain the necessary fixes to correct the business logic error. The mitigation strategy involves ensuring that all users attempting to delete protected branches must possess explicit administrative permissions, regardless of their project membership level. Security teams should conduct comprehensive audits of branch protection configurations across all GitLab instances to identify any potential exploitation attempts. This vulnerability aligns with CWE-284, which addresses improper access control, and could be categorized under ATT&CK technique T1548.001 for abuse of privileges, highlighting the importance of proper access control validation in source code management systems. The incident underscores the critical need for thorough permission model testing and validation in collaborative development platforms where code integrity is paramount to organizational security.