The Online Scheduling and Appointment Booking System WordPress plugin before 27.8 does not sanitize or properly cast a user-supplied parameter from its unauthenticated front-end booking requests before using it in a SQL query, allowing unauthenticated attackers to perform SQL injection attacks and extract sensitive data such as password hashes from the database.
https://wpscan.com/vulnerability/87e75d83-0ffc-4dd1-8839-1d5a90f5ea73/