The Appointment Booking Calendar — Simply Schedule Appointments Booking Plugin plugin for WordPress is vulnerable to blind SQL Injection in all versions up to, and including, 1.6.9.27. This is due to the db_where_conditions method in the TD_DB_Model class failing to prevent the append_where_sql parameter from being passed through JSON request bodies, while only checking for its presence in the $_REQUEST superglobal. This makes it possible for unauthenticated attackers to append arbitrary SQL commands to queries and extract sensitive information from the database via the append_where_sql parameter in JSON payloads granted they have obtained a valid public_token that is inadvertently exposed during the booking flow.