What the vulnerability does
01Description
The MC4WP: Mailchimp for WordPress plugin for WordPress is vulnerable to Missing Authorization in all versions up to, and including, 4.11.1. This is due to the plugin trusting the `_mc4wp_action` POST parameter without validation, allowing unauthenticated attackers to force the form to process unsubscribe actions instead of subscribe actions. This makes it possible for unauthenticated attackers to arbitrarily unsubscribe any email address from the connected Mailchimp audience via the `_mc4wp_action` parameter, granted they can obtain the form ID (which is publicly exposed in the HTML source).
Explanation of Vulnerability in Simple Terms
02Summary
MC4WP: Mailchimp for WordPress versions 4.11.1 and earlier lack proper authorization checks, allowing unauthenticated attackers to modify site data. The vulnerability requires no user interaction and can be exploited over the network. Site administrators should update to a version newer than 4.11.1 immediately.
What an attacker can do
03Attacker Capabilities
Modify site data without logging in or having permission to do so.
Potential impact on your site
04Site Impact
Attackers can alter plugin settings, form data, or Mailchimp integration without your knowledge or consent.
Conditions required to exploit
05Prerequisites
Network access only; no authentication or user interaction required.
Key dates
06Disclosure timeline
March 11, 2026
CVE published
April 8, 2026
Record updated
