A vulnerability was found in Keycloak where the Standard Token Exchange V2 grant path fails to enforce mTLS holder-of-key token binding. When a confidential client is configured with tls.client.certificate.bound.access.tokens set to true, Keycloak correctly rejects standard token grants if no client certificate is provided. However, an attacker who possesses the client credentials and a valid subject token can use the Standard Token Exchange V2 endpoint to obtain an active Bearer access token without presenting a TLS client certificate. The resulting token lacks the cnf.x5t#S256 claim, effectively bypassing the configured sender-constraint and allowing unauthorized access to protected resources.