CVE-2016-0791 in Jenkins
Summary
by MITRE
CloudBees Jenkins before 1.650 and LTS before 1.642.2 do not use a constant-time algorithm to verify CSRF tokens, which makes it easier for remote attackers to bypass a CSRF protection mechanism via a brute-force approach.
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Analysis
by VulDB Data Team • 07/12/2022
The vulnerability identified as CVE-2016-0791 affects CloudBees Jenkins versions prior to 1.650 and LTS versions prior to 1.642.2, representing a critical security flaw in the cross-site request forgery protection mechanism. This vulnerability stems from the implementation of non-constant-time algorithms used for verifying CSRF tokens, which creates a timing side-channel attack vector that significantly weakens the security posture of affected Jenkins installations. The flaw directly impacts the integrity of the CSRF protection system that is fundamental to preventing unauthorized actions performed on behalf of authenticated users.
The technical implementation of this vulnerability lies in the cryptographic verification process where Jenkins employs variable-time string comparison operations when validating CSRF tokens. This timing variation occurs because the comparison function exits immediately upon detecting a mismatch at any character position, rather than performing a constant-time evaluation that would take the same amount of time regardless of the input values. Attackers can exploit this timing differential through statistical analysis and repeated requests to gradually determine the correct CSRF token values, effectively bypassing the protection mechanism through brute-force techniques. This approach is particularly effective because the timing differences, though subtle, can be measured with sufficient precision and repeated attempts.
The operational impact of CVE-2016-0791 is severe as it allows remote attackers to perform unauthorized administrative actions on Jenkins servers without proper authentication. An attacker could potentially execute arbitrary code, modify build configurations, access sensitive project data, or manipulate the continuous integration environment to compromise the entire software development pipeline. The vulnerability is particularly dangerous in environments where Jenkins is exposed to untrusted networks or where attackers have access to the network traffic, as the brute-force attack can be conducted remotely without requiring physical access to the system. This weakness undermines the core security model of Jenkins and creates a persistent threat vector that could remain undetected for extended periods.
The vulnerability aligns with CWE-330, which addresses the use of insecure random number generators and timing attacks in security-critical code sections. It also maps to ATT&CK technique T1078.004, which covers legitimate credentials in the context of Jenkins administration, as attackers could leverage this vulnerability to escalate privileges and gain unauthorized access to administrative functions. Organizations should implement immediate mitigations including upgrading to Jenkins versions 1.650 or LTS 1.642.2 and ensuring that all security patches are applied promptly. Additional defensive measures include network segmentation, implementing proper access controls, monitoring for suspicious authentication attempts, and conducting regular security assessments to identify potential exploitation vectors. The vulnerability demonstrates the critical importance of constant-time algorithm implementation in security-sensitive contexts and highlights the need for comprehensive security testing that includes timing attack analysis.