The Salon Booking System WordPress plugin before 10.31.11 does not enforce a minimum of zero when subtracting a fixed-amount discount from a booking's total, allowing an unauthenticated visitor who knows a valid discount code to create a confirmed booking stored with a negative total.

The Salon Booking System WordPress plugin before 10.31.11 does not enforce a minimum of zero when subtracting a fixed-amount discount from a booking's total, allowing an unauthenticated visitor who knows a valid discount code to create a confirmed booking stored with a negative total.