Incorrect Privilege Assignment

Summary

A flaw was found in Keycloak Services versions prior to 26.2.13, 26.3.x prior to 26.4.9, and 26.5.x prior to 26.5.3. A significant Broken Access Control vulnerability exists in the UserManagedPermissionService (UMA Protection API). When updating or deleting a UMA policy associated with multiple resources, the authorization check only verifies the caller's ownership against the first resource in the policy's list. This allows a user (Owner A) who owns one resource (RA) to update a shared policy and modify authorization rules for other resources (e.g., RB) in that same policy, even if those other resources are owned by a different user (Owner B). This constitutes a horizontal privilege escalation.