MailChimp Forms by MailMunch <= 3.2.7 - Missing Authorization to Authenticated (Subscriber+) MailMunch Integration Takeover via 'sign_in' AJAX Action

Summary

The MailChimp Forms by MailMunch plugin for WordPress is vulnerable to unauthorized modification of data due to a missing capability check on the `sign_in()` and `sign_up()` AJAX handlers in all versions up to, and including, 3.2.7. This makes it possible for authenticated attackers, with Subscriber-level access and above, to relink the site's MailMunch integration to an attacker-controlled MailMunch account by submitting attacker-supplied credentials. Once relinked, all subscriber data captured by the plugin's forms is delivered to the attacker, and the forms/landing pages rendered on the site are pulled from the attacker's MailMunch account.

Timeline

1. Aug 5, 2026, 7:39 AM UTCCVE published
2. Aug 5, 2026, 1:11 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: total

3. Aug 5, 2026, 1:11 PM UTCRecord last updated

Affected versions

• mailmunch Mailmunch Forms for Mailchimp

  through 3.2.7

References 8