The Appointment Booking Calendar — Simply Schedule Appointments Booking Plugin plugin for WordPress is vulnerable to Sensitive Information Exposure in all versions up to, and including, 1.6.9.5 via the hash() function due to use of a hardcoded fall-back salt. This makes it possible for unauthenticated attackers to generate a valid token across sites running the plugin that have not manually set a salt in the wp-config.php file and access booking information that will allow them to make modifications.