The Scheduler Widget plugin for WordPress is vulnerable to Insecure Direct Object Reference in all versions up to, and including, 0.1.6. This is due to the `scheduler_widget_ajax_save_event()` function lacking proper authorization checks and ownership verification when updating events. This makes it possible for authenticated attackers, with Subscriber-level access and above, to modify any event in the scheduler via the `id` parameter granted they have knowledge of the event ID.

The Scheduler Widget plugin for WordPress is vulnerable to Insecure Direct Object Reference in all versions up to, and including, 0.1.6. This is due to the `scheduler_widget_ajax_save_event()` function lacking proper authorization checks and ownership verification when updating events. This makes it possible for authenticated attackers, with Subscriber-level access and above, to modify any event in the scheduler via the `id` parameter granted they have knowledge of the event ID.