The LearnPress – WordPress LMS Plugin for Create and Sell Online Courses plugin for WordPress is vulnerable to payment bypass through user-controlled key in all versions up to, and including, 4.3.5. This is due to improper handling of user-supplied request parameters in the REST API endpoint, which passes the unsanitized parameter array to the add_to_cart() function where array_merge() allows attacker-controlled values to overwrite hardcoded defaults. This makes it possible for authenticated attackers, with subscriber-level access and above, to enroll in any paid course entirely free of charge by supplying a quantity value of zero, which causes the order total to calculate as $0 and bypasses all payment gateway requirements.