CVE-2021-39941 in Community Edition
Summary
by MITRE • 12/13/2021
An information disclosure vulnerability in GitLab CE/EE versions 12.0 to 14.3.6, 14.4 to 14.4.4, and 14.5 to 14.5.2 allowed non-project members to see the default branch name for projects that restrict access to the repository to project members
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Analysis
by VulDB Data Team • 12/16/2021
This vulnerability represents a critical information disclosure flaw in GitLab community and enterprise editions affecting versions within specific release ranges. The issue stems from improper access control implementation where the system fails to adequately verify user permissions before exposing sensitive repository metadata. Attackers exploiting this vulnerability can gain unauthorized knowledge of default branch names for projects that should restrict repository access to project members only, effectively bypassing intended security boundaries.
The technical root cause lies in the insufficient validation of user authentication status during repository metadata retrieval operations. When non-project members attempt to access project information, the system incorrectly reveals the default branch name without proper authorization checks. This vulnerability operates at the application layer and specifically targets the project access control mechanisms within GitLab's permission system. The flaw demonstrates a clear violation of the principle of least privilege and represents a classic case of inadequate input validation and access control enforcement.
The operational impact of this vulnerability extends beyond simple information disclosure, as default branch names often contain critical information about project development status, versioning schemes, and potentially sensitive deployment strategies. An attacker could use this information to plan targeted attacks against specific branches, identify development practices, or gain insights into project architecture and security measures. The vulnerability affects all GitLab instances within the specified version ranges, making it particularly concerning for organizations with multiple installations across different environments.
From a cybersecurity perspective, this vulnerability aligns with CWE-200 (Information Exposure) and represents a significant weakness in GitLab's access control implementation. The flaw could potentially enable further attacks through reconnaissance phases where attackers gather intelligence about target systems before launching more sophisticated exploitation attempts. Organizations may find this vulnerability particularly dangerous when combined with other reconnaissance tools or when targeting projects with sensitive code repositories.
Mitigation strategies should begin with immediate patching of affected GitLab installations to versions that resolve the access control flaw. Organizations must also implement network-level monitoring to detect unusual access patterns that might indicate exploitation attempts. Regular security audits of access control configurations and proper user permission reviews should be conducted to prevent similar issues. The vulnerability highlights the importance of comprehensive testing of access control mechanisms and proper authorization validation throughout application logic. Additionally, organizations should consider implementing additional security controls such as rate limiting and enhanced logging for repository access operations to detect and prevent unauthorized access attempts.