The Block For Mailchimp – Easy Mailchimp Form Integration plugin for WordPress is vulnerable to Blind Server-Side Request Forgery in all versions up to, and including, 1.1.12 via the mcbSubmit_Form_Data(). This makes it possible for unauthenticated attackers to make web requests to arbitrary locations originating from the web application and can be used to query and modify information from internal services.
The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination.