CVE-2021-45331 in Gitea
Summary
by MITRE • 02/09/2022
An Authentication Bypass vulnerability exists in Gitea before 1.5.0, which could let a malicious user gain privileges. If captured, the TOTP code for the 2FA can be submitted correctly more than once.
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Analysis
by VulDB Data Team • 02/13/2022
The vulnerability identified as CVE-2021-45331 represents a critical authentication bypass flaw in the Gitea open-source Git service platform prior to version 1.5.0. This issue fundamentally undermines the security posture of systems relying on Gitea for version control and collaboration, as it allows unauthorized users to escalate their privileges through manipulation of the two-factor authentication mechanism. The vulnerability specifically targets the time-based one-time password implementation that serves as a crucial second layer of security for user accounts.
The technical root cause of this vulnerability lies in the improper validation and handling of TOTP (Time-Based One-Time Password) codes within the authentication flow. When a user attempts to authenticate using 2FA, the system should validate each TOTP code only once to prevent replay attacks. However, the flaw in Gitea versions before 1.5.0 allowed the same TOTP code to be submitted and accepted multiple times during the authentication process. This behavior creates a window of opportunity where an attacker who has captured a valid TOTP code can reuse it repeatedly to gain unauthorized access to user accounts without requiring the actual physical device or application that generates the codes.
From an operational perspective, this vulnerability significantly increases the attack surface for Gitea deployments and poses substantial risks to organizations relying on the platform for source code management. The impact extends beyond simple unauthorized access, as successful exploitation could lead to complete account compromise, code repository manipulation, and potential lateral movement within affected systems. The vulnerability aligns with CWE-346, which addresses "Improper Verification of Cryptographic Signature," and specifically relates to the weakness of insufficient validation of authentication tokens. Attackers could leverage this flaw to bypass the entire 2FA protection mechanism, effectively rendering the second factor authentication useless.
The security implications of this vulnerability are particularly severe given that TOTP codes are typically considered ephemeral and should only be valid for a short time window, usually 30 seconds. When the same code can be reused multiple times, it defeats the fundamental purpose of time-based authentication. This flaw essentially allows for a form of authentication replay attack that could be executed by any attacker who has intercepted a valid TOTP code through network monitoring, phishing, or other means of code capture. The vulnerability demonstrates a critical failure in the authentication state management and token validation processes within the Gitea application.
Organizations using Gitea should prioritize immediate remediation through upgrading to version 1.5.0 or later, which contains the necessary patches to address this authentication bypass vulnerability. Additional mitigations include implementing network-level monitoring to detect unusual authentication patterns, enforcing strict rate limiting on authentication attempts, and conducting thorough security audits of all user accounts that may have been exposed during the vulnerable period. The remediation process should also include reissuing TOTP codes for all affected users and implementing enhanced monitoring for authentication events. This vulnerability serves as a reminder of the critical importance of proper authentication state management and the necessity of validating all authentication tokens within security-critical applications, aligning with ATT&CK technique T1566 for credential access through social engineering and T1078 for valid accounts usage.