The Booking Calendar Contact Form plugin for WordPress is vulnerable to Insecure Direct Object Reference in all versions up to, and including, 1.2.63 via the dex_bccf_admin_int_calendar_list.inc.php file due to missing validation on a user controlled key. This makes it possible for authenticated attackers, with Subscriber-level access and above, to takeover other user's calendars and view user data associated with the calendar.