MailChimp Subscribe Forms <= 4.0.9.7 - Authenticated (Editor+) Stored Cross-Site Scripting

The MailChimp Subscribe Form, Optin Builder, PopUp Builder, Form Builder plugin for WordPress is vulnerable to Stored Cross-Site Scripting via settings in all versions up to, and including, 4.0.9.7 due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers, with editor-level permissions and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. This only affects multi-site installations and installations where unfiltered_html has been disabled.