The plugin does not sanitise and escape a parameter before outputting it back in the page, leading to a Reflected Cross-Site Scripting which could be used against a logged in high privilege users such as admin.
Visit the following URL (authenticated or not) to trigger an alert box:
http://example.com/wp-admin/admin-ajax.php?action=sac_post_type_call&post_type=</option><script>alert(`xss`);</script>