Keycloak Authorization Services resolves request URIs to protected Resources using PathMatcher (org.keycloak.common.util.PathMatcher), which performs purely lexical segment comparison with no URI normalization. Appending a matrix parameter (;x=1) or trailing / to a restricted resource URI causes it to miss the exact match and fall through to a broader, more permissive resource (e.g., the default /* catch-all).
An authenticated low-privilege user can obtain a granted RPT or positive authorization decision for resources the policy explicitly denies them. The vulnerability affects the UMA grant endpoint, the Protection API matchingUri resolution, and the client-side policy enforcer—all of which share the same unguarded PathMatcher.