CVE-2026-1781 MC4WP: Mailchimp for WordPress <= 4.11.1 - Missing Authorization to Unauthenticated Arbitrary Subscription Deletion
Unauthenticated attackers can arbitrarily unsubscribe any email address from the connected Mailchimp audience by manipulating a form parameter.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-1781?
CVE-2026-1781 is a medium-severity missing authorization vulnerability in dvankooten MC4WP: Mailchimp for WordPress, published on 11 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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).
Weakness: CWE-862
Which versions are affected by CVE-2026-1781?
How do I fix CVE-2026-1781?
No fix has been published for CVE-2026-1781 yet. Limit exposure of the affected software until one is available.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2026-1781 being exploited?
There is no known exploitation of CVE-2026-1781 in the wild and no public exploit code.
Sources
Also known as GHSA-9vm9-fm4p-mcpm.