CVE-2020-2160 in Jenkins
Summary
by MITRE
Jenkins 2.227 and earlier, LTS 2.204.5 and earlier uses different representations of request URL paths, which allows attackers to craft URLs that allow bypassing CSRF protection of any target URL.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 03/26/2020
This vulnerability exists in Jenkins versions prior to 2.227 and LTS 2.204.5 where the application employs inconsistent URL path representations that create opportunities for attackers to circumvent Cross-Site Request Forgery protection mechanisms. The flaw stems from how Jenkins processes and validates request URLs, particularly when handling different path representations such as encoded versus decoded URL components, or when dealing with multiple slashes and directory traversal sequences. Attackers can exploit this inconsistency by crafting specifically formatted URLs that appear to target legitimate endpoints but actually bypass the CSRF protection checks due to the differing path representations used internally by the application.
The technical implementation of this vulnerability allows malicious actors to construct URLs that exploit the path representation discrepancies in Jenkins' security validation logic. When Jenkins processes incoming requests, it may normalize or interpret URL paths differently depending on the internal processing pipeline, creating gaps in the CSRF protection system. This occurs because the CSRF protection mechanism relies on validating the referer header or specific URL patterns, but when these validations are performed against different path representations, attackers can craft requests that satisfy the validation criteria while actually targeting different endpoints than intended.
The operational impact of this vulnerability is significant as it allows authenticated attackers to perform unauthorized actions within the Jenkins environment without proper authorization. An attacker could potentially execute administrative functions, modify build configurations, or access restricted resources by crafting malicious URLs that bypass the CSRF protection measures. This vulnerability particularly affects Jenkins installations where users have legitimate access to the system, as the bypass mechanism does not require additional authentication credentials beyond those already available. The attack vector is particularly dangerous in environments where Jenkins is used for continuous integration and deployment processes, as it could enable unauthorized modifications to build pipelines or deployment configurations.
Organizations should immediately upgrade to Jenkins versions 2.227 or later for standard releases, and LTS 2.204.5 or later for long-term support versions to remediate this vulnerability. The mitigation strategy should also include implementing additional security controls such as network-level access restrictions, ensuring proper firewall configurations, and monitoring for suspicious URL patterns in access logs. Security teams should conduct thorough vulnerability assessments to identify any instances where Jenkins may be exposed to untrusted networks or where additional authentication layers might be necessary. This vulnerability aligns with CWE-346, which addresses the issue of "Improper Verification of Cryptographic Signature" and CWE-352, related to "Cross-Site Request Forgery," while also mapping to ATT&CK technique T1078 for valid accounts and T1566 for social engineering attacks that leverage such authentication bypasses.