What is CVE-2026-1781?

CVE-2026-1781 is a medium-severity vulnerability in Dvankooten Mc4wp: Mailchimp For Wordpress, classified under Missing Authorization. CVSS score: 6.5/10. Published 2026-03-11.

How severe is CVE-2026-1781?

Medium severity. CVSS v3 base score is 6.5 out of 10.

Auth bypass in Dvankooten Mc4wp: Mailchimp For Wordpress

CVE-2026-1781

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).

Vulnerability class: Broken Access Control

EPSS: 0.003 (18.3th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L.

Affected products

Dvankooten Mc4wp: Mailchimp For Wordpress — versions 0

Weakness classification (CWE)

CWE-862 — Missing Authorization

References

Frequently asked questions

What is CVE-2026-1781?: CVE-2026-1781 is a medium-severity vulnerability in Dvankooten Mc4wp: Mailchimp For Wordpress, classified under Missing Authorization. CVSS score: 6.5/10. Published 2026-03-11.
How severe is CVE-2026-1781?: Medium severity. CVSS v3 base score is 6.5 out of 10.