The WP Hotel Booking plugin for WordPress is vulnerable to an attack called Cross-Site Request Forgery. This issue affects versions 1.10.1 and earlier. It is due to the lack of proper security measures, called nonce validation, on the admin_add_order_item() function. This means that if an unauthenticated attacker knows how to trick a site administrator into clicking a link, they can add an order item to the website without permission.