Keycloak's SAML broker ignores ProxyRestriction instructions contained in SAML authentication messages, allowing a user to access downstream services even when the upstream identity provider explicitly forbids further delegation of the session. This flaw effectively bypasses an intended security boundary, enabling users or attackers to obtain access to services that the identity provider intended to protect.

Any deployment of Keycloak that uses the SAML broker component is impacted. The flaw is vendor‑agnostic and does not depend on a specific version or extension; all Keycloak installations that act as a SAML intermediary are potentially affected if not patched.

The CVSS score of 4.9 marks the vulnerability as medium‑severity. EPSS is not available, and no entry exists in CISA's KEV catalog. The most likely attack vector is remote, leveraging the standard SAML authentication flow; an attacker who can influence the SAML assertions exchanged between Keycloak, the upstream IdP, and downstream services can exploit the flaw by including or omitting ProxyRestriction directives to bypass the intended restriction. No local privileges are required, and the effect is purely an unauthorized access to downstream resources.