MStore API < 3.9.8 - Unauthenticated Blind SQLi

The MStore API WordPress plugin before 3.9.8 does not sanitise and escape a parameter before using it in a SQL statement, leading to a Blind SQL injection exploitable by unauthenticated users. This is only exploitable if the site owner elected to pay to get access to the plugins' pro features, and uses the woocommerce-appointments plugin.