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).
CVE-2026-1781
Score 6.5 from GitHub Security Advisory published 2026-03-11. NVD baseline CVSS 6.5; sources differ by 0.0.
- Lower severity and no public exploit yet
No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.
- CVSS v3
- 6.5
- EG Score
- 6.5(medium)
- EPSS
- 18.2%
- KEV
- Not listed
Published
March 11, 2026
Last Modified
April 22, 2026
References (7)
- security@wordfencehttps://cwe.mitre.org/data/definitions/862.html
- security@wordfencehttps://github.com/ibericode/mailchimp-for-wordpress/commit/5fdebc2a5e22d11287d011697a6b09331bd96fa5
- security@wordfencehttps://plugins.trac.wordpress.org/browser/mailchimp-for-wp/tags/4.11.1/includes/forms/class-form-listener.php#L207
- security@wordfencehttps://plugins.trac.wordpress.org/browser/mailchimp-for-wp/tags/4.11.1/includes/forms/class-form-listener.php#L53
- security@wordfencehttps://plugins.trac.wordpress.org/browser/mailchimp-for-wp/tags/4.11.1/includes/forms/class-form.php#L461
- security@wordfencehttps://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=
- security@wordfencehttps://www.wordfence.com/threat-intel/vulnerabilities/id/10262aa9-5656-4a2b-aeb5-060018798369?source=cve
Weakness Classification(1)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Data Freshness Timeline
(refreshed 16× in last 7d / 43× in last 30d)
Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.
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Related CVEs(same CWE)
Same CWE
10 shownCWE-862
Frequently asked(5)
What is CVE-2026-1781?
When was CVE-2026-1781 disclosed?
Is CVE-2026-1781 actively exploited?
What is the CVSS score of CVE-2026-1781?
How do I remediate CVE-2026-1781?
Dependency Blast Radius
Explore the affected products and dependency analysis for CVE-2026-1781
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