CVE-2026-1781

MC4WP: Mailchimp for WordPress <= 4.11.1 - Missing Authorization to Unauthenticated Arbitrary Subscription Deletion

2026-03-10 13:11
Sarawut Poolkhet (MisterHelloz)

Strategic Overview

Status
Patched in 4.12.0
Affected Plugin
MC4WP: Mailchimp for WordPress
Affected Version
<= 4.11.1
CVSS
6.5Medium
Weakness type
CWE-862 · Missing Authorization
CVE
CVE-2026-1781
View all MC4WP: Mailchimp for WordPress vulnerabilities

At a glance

CVE-2026-1781 is a medium-severity Missing Authorization vulnerability in the MC4WP WordPress plugin, affecting versions <= 4.11.1. It carries a CVSS score of 6.5 (reachable over the network; low attack complexity). Exploitation requires no authentication. The issue is fixed in version 4.12.0; sites on affected versions should update now. Disclosed March 2026, reported by Sarawut Poolkhet (MisterHelloz).

Vulnerability Overview

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).

Technical Analysis

The vector marks this flaw as remotely reachable over the network, with low attack complexity — no special timing or configuration is needed, and no privileges on the target site, and no interaction from a victim user.

CWE-862: Missing Authorization

Reaching this weakness in MC4WP <= 4.11.1 takes no account at all. A missing authorization check means a function is reachable by anyone who can reach the endpoint, because the code never asks whether the caller is allowed to perform the action.

Any user who can reach the endpoint gets to run an action reserved for higher-privileged roles, from reading protected data to changing settings or content. For MC4WP the fix is 4.12.0: builds <= 4.11.1 are affected, anything from 4.12.0 onward is not.

Remediation

Update to version 4.12.0, or a newer patched version

How does WordSec protect against this?

This one needs no account at all, which puts it outside what login hardening can reach; WordSec's login security narrows the account-level paths around it, and the firewall is what inspects the request itself. None of that substitutes for the fix: MC4WP 4.12.0 closes this, and updating the plugin is the step that ends it.

  • Login Security
  • Alerts

External References

https://www.cve.org/CVERecord?id=CVE-2026-1781https://www.wordfence.com/threat-intel/vulnerabilities/id/10262aa9-5656-4a2b-aeb5-060018798369https://nvd.nist.gov/vuln/detail/CVE-2026-1781

Related records

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