Improper input validation vulnerability in Keycloak related to the handling of matrix parameters in URL paths. The issue occurs because Keycloak, via its JAX-RS routing layer, accepts RFC-compliant matrix parameters (e.g., ;param) in path segments, while common reverse proxy configurations may ignore or mishandle them when enforcing access restrictions. A remote attacker can craft requests such as /realms;abc/master/account to mask path segments and bypass proxy-level path filtering. Although authentication is still required, this may expose administrative or sensitive endpoints that operators believe are not externally reachable. Exploitation is network-based, requires no authentication, and depends on the reverse proxy configuration in front of Keycloak.