LifterLMS <= 10.3.1 - Authenticated (Contributor+) Local File Inclusion via 'lifterlms_checkout' Shortcode Attributes

The LifterLMS – WP LMS for eLearning, Online Courses, & Quizzes plugin for WordPress is vulnerable to Local File Inclusion in versions up to, and including, 10.3.1 via attacker-controlled attributes of the [lifterlms_checkout] shortcode. This is due to the llms_get_template() helper performing extract() on the shortcode attribute array before resolving the template path, which allows the attacker-supplied 'template_name' and 'default_path' shortcode attributes to overwrite the function's local parameters and ultimately control the path passed to a PHP include. This makes it possible for authenticated attackers, with Instructor-level access and above, to include and execute arbitrary files on the server, that can be used to bypass access controls, obtain sensitive data, or achieve code execution in cases where files with safe extensions containing attacker-controlled content can be uploaded and included.