Executive brief
The Jenkins Keycloak Authentication Plugin is used to authenticate Jenkins users via Keycloak. In version 2.4.1 and earlier, the plugin fails to validate redirect URLs after successful login, allowing attackers to redirect users to arbitrary external websites. An attacker could craft a malicious login link that directs authenticated users to a phishing site, compromising user credentials and access to Jenkins systems.
Technical details
The vulnerability is an open redirect weakness in the post-login redirect mechanism of the Keycloak Authentication Plugin. The plugin does not properly validate or restrict the redirect URL parameter after a user successfully authenticates via Keycloak, allowing attackers to specify arbitrary destination URLs. An attacker can craft a specially crafted login URL and socially engineer users to click it; after authentication succeeds, the user is redirected to an attacker-controlled website where credentials or sensitive information can be harvested. The vulnerability affects versions 2.4.1 and earlier, and fixes are expected in subsequent releases.
Affected products
- Jenkins Keycloak Authentication Plugin 2.4.1 and earlier
Timeline
- 2026-09-16: disclosed
- 2026-09-16: advisory: Jenkins Security Advisory 2026-09-16