Authorization Bypass Through User-Controlled Key (CWE-639) in CalendarDeleteEventController (app/Http/Controllers/Calendar/CalendarDeleteEventController.php), exposed at GET /calendar/event/delete/{id}, in Prospero Flow CRM before 5.5.3 allows a remote, authenticated attacker to delete arbitrary calendar events belonging to other users by manipulating the {id} path parameter, because the delete handler resolves the record with Calendar::find($id)->delete() and performs no ownership check (no user_id/company_id scoping) before deletion. This results in unauthorized destruction of other users' calendar events across the platform.