MC4WP <= 4.8.6 is vulnerable to Authenticated Stored Cross-Site Scripting (XSS) vulnerability

The MC4WP: Mailchimp for WordPress plugin for WordPress is vulnerable to Stored Cross-Site Scripting via several parameters in versions up to, and including, 4.8.6 due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers with administrative 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.