Ninja Forms <= 3.15.1 - Unauthenticated Stored Cross-Site Scripting via Repeater Child 'type' Confusion via Unmatched Array Key

The Ninja Forms – The Contact Form Builder That Grows With You plugin for WordPress is vulnerable to Stored Cross-Site Scripting via Repeater Child 'type' Confusion via Unmatched Array Key in all versions up to, and including, 3.15.1 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. Exploitation requires the Ninja Forms File Uploads add-on to be active, as the attack routes the unwhitelisted child entry through the File Uploads handler to write an attacker-supplied HTML file containing arbitrary JavaScript into any web-server-writable directory, including the site root, where it is served from the site's own origin.