Permissive Cross-Origin Resource Sharing (CORS) in the REST API (helix-rest, org.apache.helix.rest.server.filters.CORSFilter) in Apache Helix through 2.0.0 on all platforms allows a remote attacker controlling a web page visited by an authorized user to read responses from and issue cross-origin requests to administrative REST endpoints via a cross-origin request from an arbitrary origin, since the filter unconditionally returns Access-Control-Allow-Origin: * together with Access-Control-Allow-Credentials: true and reflects arbitrary Access-Control-Request-Method / Access-Control-Request-Headers values in preflight responses. Users are recommended to upgrade to version 2.0.1, which fixes this issue.