The simplesamlphp-module-casserver, a CAS-compliant server module, contains an open redirect vulnerability (CWE-601) in its logout endpoint. Versions below 6.3.1 and certain 7.0.0 pre-release versions accept a URL parameter for redirection after logout without proper validation, treating the URL as trusted. This can lead to users being redirected to untrusted external sites if the configuration enables logout and skips the logout page. The issue is resolved in versions 6.3.1 and 7.0.0.

An attacker can exploit this vulnerability to redirect users to arbitrary, potentially malicious external websites after logout, which may facilitate phishing or social engineering attacks. There is no direct impact on confidentiality or availability, but the integrity of user navigation flow is compromised. The CVSS base score of 4.7 reflects a medium severity with no confidentiality or availability impact but some integrity impact.

Upgrade affected installations of simplesamlphp-module-casserver to version 6.3.1 or later, or to version 7.0.0 or later where the issue is fixed. Since this is a module vulnerability and not a cloud service, manual patching by updating the software is required. There is no vendor advisory explicitly stating otherwise, so applying the official fixed versions is the recommended remediation.