Availability Calendar <= 1.2.6 - Cross-Site Request Forgery via add_availability_calendar_create_admin_page()

Description

The Availability Calendar plugin for WordPress is vulnerable to Cross-Site Request Forgery in versions up to, and including, 1.2.6. This is due to missing or incorrect nonce validation on the add_availability_calendar_create_admin_page() function. This makes it possible for unauthenticated attackers to create an availability window via a forged request granted they can trick a site administrator into performing an action such as clicking on a link.