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6.5

Mailchimp for WordPress Plugin Allows Unauthenticated Unsubscribes

CVE-2026-1781
Summary

The Mailchimp for WordPress plugin is vulnerable to a security issue that allows attackers to remove email addresses from your Mailchimp list without permission. This can happen if an attacker knows the form ID, which is easily visible in the plugin's code. To protect your list, update the plugin to the latest version.

Original title
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` P...
Original description
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).
nvd CVSS3.1 6.5
Vulnerability type
CWE-862 Missing Authorization
Published: 11 Mar 2026 · Updated: 13 Mar 2026 · First seen: 11 Mar 2026