The Salon Booking System WordPress plugin before 10.31.11 does not restrict one of its REST API endpoints to salon staff, allowing any authenticated user, such as a subscriber, to retrieve every discount coupon configured on the site, including coupons the administrator has chosen to hide from customers, together with their amounts, validity dates and usage limits.
https://wpscan.com/vulnerability/146eaa60-08e8-43b2-8d87-74e79261d422/