Blind SSRF behavior in the CIBA implementation of Keycloak. The issue arises because the backchannel_client_notification_endpoint configured during Dynamic Client Registration or client administration is not sufficiently validated before use. An attacker with high privileges (Administrator access or a valid Initial Access Token) can configure this endpoint to point to arbitrary internal URLs, including localhost or cloud metadata services. When a CIBA authentication request is initiated in ping mode, Keycloak sends a blind POST request to the configured endpoint. While the attacker cannot observe the response, the behavior allows limited influence over server-side network interactions and may enable abuse of internal services.