Events Manager < 7.3.7 - Unauthenticated SQL Injection via PHP Object Injection in Booking Registration

The Events Manager WordPress plugin before 7.3.7 does not safely handle booking-registration data on sites using No-User-Account Booking Mode: a booker-supplied registration field is stored as booking meta and later deserialized without restricting allowed classes, enabling PHP object injection. The resulting gadget chain reaches a database query that is built without parameterisation, so an unauthenticated attacker can read arbitrary database data (e.g. user password hashes, secret keys) when the booking is later loaded.