Keycloak's Dynamic Client Registration feature contains a vulnerability that allows attackers with valid tokens to register malicious applications. These applications can forge identity claims in signed tokens by manipulating protected fields such as user ID (sub) and audience (aud). This flaw enables impersonation of other users and unauthorized access to services relying on these tokens. Exploitation requires possession of a valid Initial Access Token and a realm account. No official fix or mitigation meeting Red Hat's criteria is currently available.