The Formidable Forms – Contact Form Plugin, Survey, Quiz, Payment, Calculator Form & Custom Form Builder plugin for WordPress is vulnerable to POST-Based Reflected Cross-Site Scripting via the Custom HTML Form parameters in all versions up to, and including, 6.16.1.2 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that execute if they can successfully trick a user into performing an action such as clicking on a link.
The Formidable Forms WordPress plugin before 6.14.1 does not sanitise and escape some of its settings, which could allow high privilege users such as admin to perform Stored Cross-Site Scripting attacks even when the unfiltered_html capability is disallowed (for example in multisite setup).