LearnDash LMS <= 5.1.5 - Authenticated (Subscriber+) Arbitrary File Upload via Assignment Upload Handler

The LearnDash LMS plugin for WordPress is vulnerable to Unrestricted File Type Upload in versions up to and including 5.1.5. This is due to insufficient input validation in the 'learndash_fileupload_process' function, which iterates through an entire array and validates only the first file. This makes it possible for authenticated attackers, with subscriber-level access and above who are enrolled in a course with assignment uploads enabled, to upload arbitrary disallowed files, including PHP files, to the server's wp-content/uploads/learndash/assignments/ directory. The uploaded files can only be used for Remote Code Execution if default server configurations have been changed to allow for execution.