CVE-2024-23903 in GitLab Branch Source Plugin
Summary
by MITRE • 01/24/2024
Jenkins GitLab Branch Source Plugin 684.vea_fa_7c1e2fe3 and earlier uses a non-constant time comparison function when checking whether the provided and expected webhook token are equal, potentially allowing attackers to use statistical methods to obtain a valid webhook token.
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Analysis
by VulDB Data Team • 08/30/2024
The vulnerability identified as CVE-2024-23903 affects the Jenkins GitLab Branch Source Plugin version 684.vea_fa_7c1e2fe3 and earlier, presenting a significant security risk through its implementation of webhook token validation. This flaw resides in the plugin's handling of authentication tokens used to verify incoming webhook requests from GitLab, creating an avenue for attackers to exploit timing variations in token comparison operations.
The technical core of this vulnerability stems from the use of a non-constant time comparison function during the validation process of webhook tokens. When comparing two strings or tokens, a constant-time comparison ensures that the comparison takes the same amount of time regardless of the input values, making it resistant to timing-based attacks. However, the affected plugin employs a standard equality check that varies in execution time depending on where the first mismatch occurs within the token strings. This timing variation creates measurable differences that can be exploited through statistical analysis to deduce valid webhook tokens incrementally.
This vulnerability directly maps to CWE-203, which describes "Observable Behavioral Differences," and more specifically aligns with CWE-320, "Cryptography Weaknesses," as it exposes cryptographic token validation to timing attacks. The operational impact of this vulnerability extends beyond simple credential theft, as successful exploitation could enable attackers to gain unauthorized access to Jenkins pipelines, potentially leading to code injection, data breaches, or complete system compromise through unauthorized build execution. Attackers could leverage side-channel timing attacks to systematically determine valid webhook tokens by measuring response times during authentication attempts.
The attack surface is particularly concerning for organizations using Jenkins as part of their continuous integration and deployment pipelines, where GitLab webhook integrations are common for triggering automated builds upon code changes. This vulnerability affects the integrity of the webhook authentication mechanism, which is critical for maintaining secure communication between GitLab repositories and Jenkins servers. The timing-based approach to token extraction aligns with techniques described in the MITRE ATT&CK framework under T1566, "Phishing," and T1078, "Valid Accounts," as it enables attackers to obtain legitimate credentials through indirect means rather than direct brute force.
Organizations should immediately upgrade to Jenkins GitLab Branch Source Plugin version 685.vea_fa_7c1e2fe3 or later, which implements constant-time token comparison functions to address this vulnerability. Additional mitigations include implementing network-level restrictions on webhook endpoints, using additional authentication layers such as IP whitelisting, and monitoring for unusual authentication patterns that might indicate timing-based attacks. Security teams should also consider implementing automated vulnerability scanning tools that can detect the presence of this specific vulnerability in their Jenkins environments. The remediation process should include thorough testing to ensure that the updated plugin maintains full functionality while eliminating the timing attack vector.