MC4WP: Mailchimp for WordPress <= 4.11.1 - Missing Authorization to Unauthenticated Arbitrary Subscription Deletion
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Security bypass
- Confidentiality · integrity · availability
- None · Low · Low
- Fix status
- No fix listed
Attack profile from CVSS 3.1 · CNA. Fix status from CNA. Impact type from CWE-862.
Summary
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).
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- Yes
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| dvankooten | MC4WP: Mailchimp for WordPress | up to 4.11.1 | — | No fix listed | CNA |
- MC4WP: Mailchimp for WordPress Vendordvankooten Affected up to 4.11.1 Fixed in — No fix listed CNA
Remediation
No fixed version listed by the sources yet.
Timeline
- 2026-10-02 Threatist record created from CVE-2026-1781
- 2026-10-03 Alias added: GHSA-9vm9-fm4p-mcpm
References
Other 7
- 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=
More dvankooten vulnerabilities
- TI-2026-18342 SQL injection in dvankooten koko-analytics CVSS 3.1HIGH 8.4
- TI-2024-08546 MC4WP: Mailchimp Top Bar <= 1.6.0 - Reflected Cross-Site Scripting CVSS 3.1MEDIUM 6.1
- TI-2017-13750 The mailchimp-for-wp plugin before 4.1.8 for WordPress has XSS via the return value of add_query_arg. CVSS 3.0MEDIUM 6.1
- TI-2016-08909 The mailchimp-for-wp plugin before 4.0.11 for WordPress has XSS on the integration settings page. CVSS 3.0MEDIUM 6.1
- TI-2026-03965 Cross-site scripting in dvankooten MC4WP: Mailchimp for WordPress CVSS 3.1MEDIUM 6.4
- TI-2024-09001 Social Sharing (by Danny) <= 1.3.7 - Authenticated (Contributor+) Stored Cross-Site Scripting via Shortcode CVSS 3.1MEDIUM 6.4
Sources
- CVE-2026-1781 · CVE Program
- CVE-2026-1781 · NVD
- FIRST EPSS
- GHSA-9vm9-fm4p-mcpm · GitHub Advisory Database · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences