A critical authorization flaw in the Mailmunch Forms for Mailchimp plugin allows authenticated attackers to perform unauthorized data modifications via AJAX handlers.

The plugin fails to perform necessary capability checks on the sign_in() and sign_up() AJAX handlers. This permits an authenticated user with low privileges to trigger these functions, leading to unauthorized modification of data within the plugin environment.

This vulnerability may allow attackers to manipulate user data or subscription settings, potentially leading to unauthorized access or data corruption. The CVSS score of 8.1 reflects the high risk posed by the ability to perform unauthorized actions within the administrative context of the plugin, threatening both data integrity and system security.

Immediate Action: Update the Mailmunch Forms for Mailchimp plugin to version 3.2.8 or the latest available version to restore proper authorization checks.

Proactive Monitoring: Monitor site activity for unusual usage of AJAX endpoints, particularly those related to sign-in or sign-up functions, and check for unexpected modifications in user subscription lists.

Compensating Controls: Use a WAF to restrict access to the plugin's administrative AJAX endpoints and ensure that only authorized users have the capability to interact with these functions.

Public Exploit Available: Unknown

Administrators must update the Mailmunch Forms for Mailchimp plugin immediately to resolve this authorization deficiency. Regularly auditing user roles and capabilities is recommended to minimize the risk of low-privileged users exploiting such vulnerabilities.