The Ninja Forms - File Uploads Extension WordPress plugin is vulnerable to reflected cross-site scripting due to missing sanitization of the files filename parameter found in the ~/includes/ajax/controllers/uploads.php file which can be used by unauthenticated attackers to add malicious web scripts to vulnerable WordPress sites, in versions up to and including 3.3.12.
The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.