🟡 Keycloak-services: keycloak-services: required signed-jwt assertion policy can be bypassed with unsigned assertion headers (Red Hat Red Hat build of Keycloak 26.6)

Description

Keycloak provides a mechanism called Client Policies to enforce security requirements on clients, such as requiring them to use signed JWTs for authentication. A flaw was discovered where this enforcement can be bypassed. An attacker with valid client credentials can provide a fake, unsigned assertion header that tricks the system into thinking the policy requirements have been met. This allows the attacker to authenticate using simpler methods like a client secret even when the administrator has mandated more secure, signed assertions.