# MC4WP: Mailchimp for WordPress <= 4.14.1 - Unauthenticated Insecure Direct Object Reference to Arbitrary Audience Subscription via '_mc4wp_lists' Parameter

- **ID:** WPSEC-2026-2462
- **Plugin:** MC4WP: Mailchimp for WordPress (`mailchimp-for-wp`), https://wordpress.org/plugins/mailchimp-for-wp/
- **Affected versions:** all versions before 4.15.0
- **Fixed in:** 4.15.0 (Update to 4.15.0 or later.)
- **Severity:** Medium 5.3 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N)
- **Weakness:** CWE-639
- **Usage among sites WPSec scans:** plugin High, affected versions High (as of 2026-11-04)
- **Attack surface analysis:** https://attacksurface.wpsec.com/plugin/mailchimp-for-wp
- **Fix released:** 2026-11-03
- **Published:** 2026-11-04
- **URL:** https://wpsec.com/vuln/WPSEC-2026-2462/

## Description

The MC4WP: Mailchimp for WordPress plugin for WordPress is vulnerable to Insecure Direct Object Reference via the '_mc4wp_lists' parameter in all versions up to, and including, 4.14.1. This is due to sign-up form submissions and integrations (such as the comment form, registration form and Contact Form 7) accepting user-supplied Mailchimp list IDs without checking that the site owner selected those lists for that form or integration. This makes it possible for unauthenticated attackers to subscribe arbitrary email addresses to any audience in the connected Mailchimp account.

## References

- https://wpsec.com/vuln/WPSEC-2026-2462/
- https://plugins.svn.wordpress.org/mailchimp-for-wp/tags/4.15.0/
- https://wordpress.org/plugins/mailchimp-for-wp/

Source: WPSec, https://wpsec.com/vuln/WPSEC-2026-2462/

License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Free to use, share and adapt, also commercially, if you credit WPSec and link to this advisory.