File Manager Pro <= 8.3.9 - Cross-Site Request Forgery to Arbitrary File Upload

The File Manager Pro plugin for WordPress is vulnerable to Cross-Site Request Forgery in all versions up to, and including, 8.3.9. This is due to missing or incorrect nonce validation on the 'mk_file_folder_manager' ajax action. This makes it possible for unauthenticated attackers to upload arbitrary files via a forged request granted they can trick a site administrator into performing an action such as clicking on a link.