EUVD-2026-36021
GHSA-463r-5m89-4xfr
Severity by source
AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
Primary rating from Vendor (jenkins).
CVSS VectorVendor: jenkins
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
Lifecycle Timeline
3DescriptionCVE.org
Jenkins 2.567 and earlier, LTS 2.555.2 and earlier improperly determines that a redirect URL after login is legitimately pointing to Jenkins when it contains tab or newline characters between //, allowing attackers to perform phishing attacks.
AnalysisAI
Open redirect in Jenkins login flow enables phishing attacks by exploiting improper redirect URL validation. Tab or newline characters injected between // in a post-login redirect URL bypass Jenkins' legitimacy check, redirecting authenticated victims to attacker-controlled sites. Affects Jenkins weekly 2.567 and earlier and LTS 2.555.2 and earlier; vendor-released patches are available. No public exploit identified at time of analysis, and no CISA KEV listing exists, but the bypass technique is trivially derivable from the public advisory.
Technical ContextAI
Jenkins implements a post-login redirect mechanism intended to return users to their destination within the Jenkins application after completing authentication. CWE-601 (URL Redirection to Untrusted Site / Open Redirect) describes the root cause class: insufficient validation of user-supplied redirect URLs. The specific bypass exploits a parsing inconsistency - Jenkins' URL validation logic does not account for whitespace control characters (tab \t, newline \n) embedded between // in the redirect value. These characters are normalized or stripped by browsers during navigation but are not normalized by Jenkins' validator, so a crafted URL passes the legitimacy check while resolving to an external domain in the browser. The CPE string cpe:2.3:a:jenkins_project:jenkins:*:*:*:*:*:*:*:* confirms this affects the core Jenkins application across all platforms and deployment types, as reported by the Jenkins project itself.
RemediationAI
Vendor-released patches are available: upgrade Jenkins weekly to version 2.568 or later, or upgrade Jenkins LTS to version 2.555.3 or later. These fix versions are confirmed by EUVD-2026-36021 and the Jenkins security advisory at https://www.jenkins.io/security/advisory/2026-06-10/#SECURITY-3711+3755. If immediate patching is not feasible, restrict the Jenkins login endpoint to trusted internal networks or VPN-only access - this eliminates the attacker's ability to distribute phishing login URLs to users who access Jenkins from external networks, though it does not address insider or already-networked threat actors. As an additional control, configure web application firewall rules to strip or reject login redirect parameters containing tab (%09) or newline (%0A, %0D) encoded characters. Note that user-awareness training (instructing users to verify the URL bar after login) is a weak compensating control and should not substitute for patching.
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