The Post Duplicator plugin for WordPress is vulnerable to unauthorized arbitrary protected post meta insertion in all versions up to, and including, 3.0.8. This is due to the `duplicate_post()` function in `includes/api.php` using `$wpdb->insert()` directly to the `wp_postmeta` table instead of WordPress's standard `add_post_meta()` function, which would call `is_protected_meta()` to prevent lower-privileged users from setting protected meta keys (those starting with `_`). This makes it possible for authenticated attackers, with Contributor-level access and above, to inject arbitrary protected post meta keys such as `_wp_page_template`, `_wp_attached_file`, and other sensitive meta keys on duplicated posts via the `customMetaData` JSON array parameter in the `/wp-json/post-duplicator/v1/duplicate-post` REST API endpoint.