wp-downloadmanager: Unrestricted File Upload via Missing Extension/MIME Validation and Path Traversal

The wp-downloadmanager WordPress plugin, in version 1.68.11 (also affecting the 6.9.4 release line), allows an admin-privileged user (current_user_can('manage_downloads')) to upload arbitrary files via download-add.php with no extension or MIME-type validation of any kind - no wp_check_filetype_and_ext(), no validate_file(), and no extension blocklist exist anywhere in the upload handler. The destination path is additionally built by concatenating the raw, unsanitized $_POST['file_upload_to'] value with no traversal check (no ../ filtering, no basename()/realpath() applied). Since the base download path is required to live under WP_CONTENT_DIR (a web-accessible location), an uploaded PHP file lands in a web-servable path and can be directly executed, resulting in remote code execution. The plugin's own later changelog confirms these protections were absent in this version: v1.69 added file-type validation via wp_check_filetype_and_ext(), and v1.69.1 added directory-traversal protection - neither existed in 1.68.11.