The Forms for Mailchimp by Optin Cat – Grow Your MailChimp List plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the form color parameters in all versions up to, and including, 2.5.6 due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers, with editor-level access, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.