OpenEMR: Unauthenticated Open Redirect via OIDC End Session Endpoint

OpenEMR is a free and open source electronic health records and medical practice management application. Prior to 8.3.0, userSessionLogout() in src/RestControllers/AuthorizationController.php uses decodeToken() to process an id_token_hint without verifying its signature and, when the referenced trusted session is absent, redirects to the caller-supplied post_logout_redirect_uri before validating it against the client's registered redirect URIs. An unauthenticated attacker can craft a logout link that sends a user to an arbitrary external site and invalidates the user's session, enabling convincing phishing flows from the legitimate logout endpoint. The endpoint is reachable when the OpenEMR REST API is enabled. This issue is fixed in version 8.3.0.