Jenkins SAML Plugin: no replay cache lets a captured SAML response be reused to log in as that user

Impact

Jenkins SAML Plugin 4.583.vc68232f7018a_ and earlier keeps no replay cache, so a SAML response that has already been consumed is still accepted. Anyone who can observe the SAML authentication exchange between a user's browser and Jenkins can replay those requests and end up authenticated as that user. On a GPU fleet the Jenkins controller is usually the thing that holds cloud credentials, registry push tokens and the job definitions that run on the training and build nodes, so an identity takeover there is a route into the fleet rather than a single compromised account. If the replayed identity is an administrator, it includes the ability to run arbitrary pipeline code on connected agents.

Who can reach it

A network-position attacker who can obtain the SAML authentication flow for a victim's login (proxy, TLS-terminating middlebox, logs, browser history or referrer leakage). No Jenkins credentials of their own are needed; the victim must have completed a login, and the CVSS vector records required user interaction and high attack complexity.

What to do

The record points only to Jenkins security advisory 2025-10-29 (SECURITY-3613) and does not name a fixed plugin release, so do not assume one exists - check the advisory for current status before planning the work. Until a fixed version is published, reduce exposure of the SAML exchange: terminate TLS only at Jenkins or at a trusted proxy, keep the controller off shared ingress paths, shorten SAML assertion validity at the identity provider, and audit logins of privileged accounts. When a fixed plugin does land, updating it requires restarting the Jenkins controller, which drains or kills in-flight jobs on GPU agents.

References

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