The Appointment Hour Booking – Booking Calendar plugin for WordPress is vulnerable to Stored Cross-Site Scripting via form field configuration parameters in all versions up to, and including, 1.5.60 due to insufficient input sanitization and output escaping on the 'Min length/characters' and 'Max length/characters' field configuration values. This makes it possible for authenticated attackers, with administrator-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses the form builder interface. This only affects multi-site installations and installations where unfiltered_html has been disabled.