The WP-Optimize plugin for WordPress is vulnerable to unauthorized access of functionality due to missing capability checks in the `receive_heartbeat()` function in `includes/class-wp-optimize-heartbeat.php` in all versions up to, and including, 4.5.0. This is due to the Heartbeat handler directly invoking `Updraft_Smush_Manager_Commands` methods without verifying user capabilities, nonce tokens, or the allowed commands whitelist that the normal AJAX handler (`updraft_smush_ajax`) enforces. This makes it possible for authenticated attackers, with Subscriber-level access and above, to invoke admin-only Smush operations including reading log files (`get_smush_logs`), deleting all backup images (`clean_all_backup_images`), triggering bulk image processing (`process_bulk_smush`), and modifying Smush options (`update_smush_options`).