The Piotnet Forms WordPress plugin through 1.0.30 does not authenticate or validate a form-submission file-upload request and permits browser-renderable file types to be stored, allowing unauthenticated attackers to store a file that executes arbitrary JavaScript in the site's origin when it is opened (Stored XSS).

The Piotnet Forms plugin for WordPress is vulnerable to arbitrary file upload due to missing file type validation in the 'piotnetformsajaxformbuilder' function in all versions up to, and including, 2.1.40. The plugin uses an incomplete extension blacklist that only blocks php, phpt, php5, php7, and exe extensions, while allowing dangerous extensions such as .phar or .phtml to be uploaded. This makes it possible for unauthenticated attackers to upload arbitrary files on the affected site's server which may make remote code execution possible. Note: The exploit can only be exploited if a file field is added to the form.