MasterStudy LMS plugin for WordPress before 3.7.50 contains a missing authorization vulnerability that allows any authenticated user, including Subscribers, to trigger the stm_lms_send_test_email_ajax AJAX action without capability or nonce validation. Attackers can invoke this handler directly or via cross-site request forgery to cause an uncaught PHP fatal error that, when display_errors is enabled, discloses the absolute filesystem path of the plugin.