WPFunnels < 3.8.0 - Authenticated (Contributor+) Stored Cross-Site Scripting via 'wpf_optin_form' Shortcode

Description

The WPFunnels – Easy Funnel Builder To Optimize Buyer Journeys And Get More Leads & Sales plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'wpf_optin_form' shortcode in all versions up to, and including, 3.7.9 due to insufficient input sanitization and output escaping of the 'button_icon' parameter. This makes it possible for authenticated attackers, with contributor level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.