Paid Downloads <= 3.15 - Unauthenticated Arbitrary File Upload via 'paiddownloads_update_file' Action

The Paid Downloads plugin for WordPress is vulnerable to Arbitrary File Upload in all versions up to, and including, 3.15 via the admin_request_handler function. This is due to missing authorization and file type validation in the admin_request_handler function, which is reachable unauthenticated via is_admin() returning true for /wp-admin/admin-post.php. This makes it possible for unauthenticated attackers to upload files that may be executable, which makes remote code execution possible. On Apache servers where AllowOverride is enabled, an .htaccess file placed in the upload directory may block direct HTTP retrieval of uploaded files, limiting exploitability to stacks that do not honor .htaccess directives such as nginx, LiteSpeed, and Apache with AllowOverride None.