CVE-2021-39874 in Community Edition
Summary
by MITRE • 10/04/2021
In all versions of GitLab CE/EE since version 11.0, the requirement to enforce 2FA is not honored when using git commands.
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Analysis
by VulDB Data Team • 10/08/2021
The vulnerability identified as CVE-2021-39874 represents a critical security flaw in GitLab Community Edition and Enterprise Edition versions 11.0 and later, where the mandatory two-factor authentication enforcement mechanism fails to properly validate user authentication status during git operations. This weakness allows authenticated users to bypass the required two-factor authentication protocol when performing git commands, effectively undermining the security controls that organizations have implemented to protect their source code repositories and development environments. The issue stems from the improper handling of authentication contexts within GitLab's git protocol implementation, where the system fails to verify that users have completed the required two-factor authentication process before granting access to git operations.
This technical flaw operates at the intersection of authentication and authorization controls within GitLab's security framework, specifically affecting the enforcement of multi-factor authentication policies. The vulnerability exists because GitLab's git command processing does not adequately validate whether a user has completed the required two-factor authentication step, even when administrators have explicitly configured the system to enforce such requirements. This misconfiguration allows attackers to leverage legitimate user credentials to perform git operations without the additional security layer that should be mandatory. The flaw particularly impacts organizations that rely on GitLab for version control and collaborative development, where the compromise of user accounts could lead to unauthorized code modifications, data exfiltration, or repository corruption.
The operational impact of CVE-2021-39874 extends beyond simple authentication bypass, as it creates potential attack vectors for privilege escalation and unauthorized access to sensitive development environments. When users authenticate through the web interface with 2FA enabled, they may still be able to perform git operations without the additional authentication factor, effectively rendering the security control ineffective. This vulnerability aligns with CWE-305 authentication bypass issues and can be categorized under ATT&CK technique T1566.001 for credential harvesting through social engineering, as attackers can exploit this weakness to gain access to repositories that should be protected by additional authentication requirements. The flaw particularly affects organizations with strict security policies requiring 2FA for all administrative and development activities, as it allows bypass of these controls during routine git operations.
Organizations affected by this vulnerability should immediately implement mitigations that include updating to patched versions of GitLab where the authentication bypass has been resolved. The recommended approach involves ensuring that all GitLab instances are upgraded to versions that properly enforce 2FA requirements for git operations, as the vulnerability has been addressed in subsequent releases. Security teams should also conduct comprehensive audits of their GitLab configurations to verify that 2FA enforcement policies are properly implemented and monitored. Additional mitigations include implementing network-level controls to restrict access to git operations, monitoring for unusual authentication patterns, and ensuring that security policies are consistently enforced across all GitLab components. The vulnerability demonstrates the importance of proper authentication context handling in distributed systems and highlights the need for comprehensive security testing that includes edge cases in authentication flows. This issue serves as a reminder that security controls must be consistently enforced across all application interfaces and protocols, particularly in development environments where access to source code repositories represents a significant attack surface.