The WP Voting Contest WordPress plugin before 3.0 does not sanitise and escape the post_id parameter before outputting it back in the response via the wpvc_social_share_icons AJAX action (available to both unauthenticated and authenticated users), leading to a Reflected Cross-Site Scripting issue
https://wpscan.com/vulnerability/286b81a0-6f6d-4024-9bbc-6cb373990a7a