The Mailchimp List Subscribe Form plugin for WordPress is vulnerable to Cross-Site Request Forgery in all versions up to, and including, 2.0.0. This is due to missing or incorrect nonce validation on the mailchimp_sf_change_list_if_necessary() function. This makes it possible for unauthenticated attackers to change Mailchimp lists via a forged request granted they can trick a site administrator into performing an action such as clicking on a link.