CVE-2021-39879 in Community Edition
Summary
by MITRE • 10/04/2021
Missing authentication in all versions of GitLab CE/EE since version 7.11.0 allows an attacker with access to a victim's session to disable two-factor authentication
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Analysis
by VulDB Data Team • 10/09/2021
This vulnerability represents a critical authentication bypass flaw in GitLab Community and Enterprise editions affecting all versions since 7.11.0. The issue stems from a design weakness where the system fails to properly validate user authentication status during sensitive operations, specifically targeting the two-factor authentication disable functionality. Attackers can exploit this weakness by leveraging a victim's existing session to perform administrative actions without proper authorization, effectively undermining the security controls that protect user accounts. The vulnerability operates at the application level and demonstrates poor input validation and session management practices that violate fundamental security principles.
The technical implementation of this flaw allows an unauthenticated attacker to manipulate session tokens and execute privileged operations through the GitLab web interface. When a user's session is compromised or intercepted, the system does not adequately verify that the requesting user possesses the necessary authentication credentials before allowing modifications to two-factor authentication settings. This represents a failure in the principle of least privilege and demonstrates a lack of proper access control enforcement within the application's security architecture. The vulnerability can be classified under CWE-287 which addresses improper authentication scenarios, and aligns with ATT&CK technique T1566 for credential harvesting and T1078 for valid accounts usage.
The operational impact of this vulnerability is severe as it enables attackers to completely compromise user accounts by removing two-factor authentication protections. Once an attacker gains access to a victim's session, they can effectively lock out legitimate users while maintaining persistent access to the compromised account. This creates a scenario where attackers can maintain long-term access to GitLab repositories, potentially leading to code tampering, data exfiltration, or further network infiltration through compromised development environments. The vulnerability affects organizations that rely on GitLab for source code management, CI/CD pipelines, and collaborative development workflows where unauthorized access could result in significant operational and financial damage.
Organizations should implement immediate mitigations including enforcing strict session management policies, implementing additional authentication layers, and monitoring for suspicious administrative activities. The recommended approach involves upgrading to patched versions of GitLab where the authentication bypass has been resolved, typically through version 14.1.1 or later depending on the specific edition. Security teams should also deploy session monitoring solutions that can detect anomalous authentication patterns and implement multi-factor authentication requirements for all administrative accounts. Additional protective measures include network segmentation, regular security auditing of session tokens, and ensuring that all users have strong authentication methods in place. The vulnerability highlights the importance of proper authentication design and demonstrates why continuous security testing and validation of access control mechanisms are essential for maintaining secure software environments.