CVE-2026-1303: MailChimp Campaigns Auth Bypass Flaw

CVE-2026-1303 Overview

The MailChimp Campaigns plugin for WordPress contains a Missing Authorization vulnerability (CWE-862) in all versions up to and including 3.2.4. The vulnerability exists due to missing capability checks on the mailchimp_campaigns_manager_disconnect_app function, which is hooked to an AJAX action of the same name. This security flaw allows authenticated attackers with Subscriber-level access or above to disconnect the WordPress site from its MailChimp synchronization app, disrupting automated email campaigns and marketing integrations.

Critical Impact

Authenticated attackers with minimal privileges (Subscriber-level) can disrupt business-critical email marketing operations by disconnecting MailChimp integration without proper authorization.

Affected Products

• MailChimp Campaigns plugin for WordPress versions up to and including 3.2.4
• WordPress sites utilizing the olalaweb-mailchimp-campaign-manager plugin
• Any WordPress installation with affected plugin versions enabled

Discovery Timeline

• 2026-02-14 - CVE-2026-1303 published to NVD
• 2026-02-18 - Last updated in NVD database

Technical Details for CVE-2026-1303

Vulnerability Analysis

This vulnerability represents a classic Missing Authorization flaw (CWE-862) in WordPress plugin architecture. The affected function mailchimp_campaigns_manager_disconnect_app is registered as an AJAX action handler but fails to implement proper capability checks before executing privileged operations. In WordPress, AJAX actions are commonly used to handle asynchronous requests, but without proper authorization controls, any authenticated user can invoke these actions regardless of their intended role restrictions.

The vulnerability allows users with the lowest authenticated privilege level (Subscriber) to perform actions that should be restricted to administrators or users with campaign management capabilities. The attack can be executed remotely over the network without requiring any user interaction, making it relatively straightforward to exploit.

Root Cause

The root cause of this vulnerability lies in the absence of capability checks within the mailchimp_campaigns_manager_disconnect_app function. When registering AJAX actions in WordPress, developers must explicitly verify that the requesting user has the appropriate capabilities (such as manage_options or a custom capability) before performing sensitive operations. The vulnerable code at line 636 of mailchimp-campaigns-manager.php processes the disconnect request without validating whether the authenticated user should have permission to disconnect the MailChimp integration.

Attack Vector

An attacker exploiting this vulnerability would need to:

1. Obtain any authenticated access to the target WordPress site (even a basic Subscriber account)
2. Send a crafted AJAX request to the mailchimp_campaigns_manager_disconnect_app action endpoint
3. The server processes the request without verifying authorization and disconnects the MailChimp integration

The vulnerability requires network access and authentication but no user interaction. Since WordPress Subscriber accounts are often easy to obtain (through open registration or social engineering), the attack surface for this vulnerability can be significant on sites with public registration enabled.

The vulnerable code lacks proper authorization checks. For technical details, see the WordPress Plugin Mailchimp Code in the WordPress plugin repository.

Detection Methods for CVE-2026-1303

Indicators of Compromise

• Unexpected disconnection of MailChimp integration without administrator action
• Failed or halted automated email campaigns that were previously functioning
• WordPress AJAX requests to mailchimp_campaigns_manager_disconnect_app from non-administrative user accounts
• Audit log entries showing Subscriber-level users accessing plugin management functions

Detection Strategies

• Monitor WordPress AJAX action logs for requests to mailchimp_campaigns_manager_disconnect_app from users without administrative privileges
• Implement web application firewall (WAF) rules to detect suspicious AJAX requests to the vulnerable endpoint
• Review user activity logs for Subscriber accounts making administrative-type requests
• Set up alerts for MailChimp integration status changes that don't correlate with administrator sessions

Monitoring Recommendations

• Enable detailed logging for all WordPress AJAX actions and correlate with user privilege levels
• Configure MailChimp integration status monitoring with alerts for unexpected disconnections
• Implement real-time monitoring of plugin-related AJAX endpoints for unusual access patterns
• Review authentication logs for potential credential compromise that could enable this attack

How to Mitigate CVE-2026-1303

Immediate Actions Required

• Update the MailChimp Campaigns plugin to a patched version beyond 3.2.4 immediately
• Temporarily disable the plugin if an update is not yet available and the functionality is not critical
• Review recent user activity logs to determine if the vulnerability has been exploited
• Verify current MailChimp integration status and re-establish connection if disconnected

Patch Information

Users should update to the latest version of the MailChimp Campaigns plugin available through the WordPress plugin repository. The patched version should include proper capability checks on the mailchimp_campaigns_manager_disconnect_app function. Review the WordPress Plugin Mailchimp Latest Code to verify the fix implementation. Additional vulnerability details are available in the Wordfence Vulnerability Report.

Workarounds

• Restrict user registration on WordPress sites to prevent attackers from obtaining Subscriber accounts
• Implement additional access controls at the web server or WAF level to block AJAX requests to the vulnerable endpoint from non-administrative users
• Use a security plugin to add capability checks to unprotected AJAX actions
• Consider temporarily deactivating the plugin until an official patch is released

# Configuration example - Block vulnerable AJAX action at .htaccess level
# Add to WordPress .htaccess file as temporary mitigation
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteCond %{REQUEST_URI} ^.*wp-admin/admin-ajax\.php.*$ [NC]
RewriteCond %{QUERY_STRING} action=mailchimp_campaigns_manager_disconnect_app [NC]
RewriteCond %{HTTP_COOKIE} !wordpress_logged_in.*administrator [NC]
RewriteRule .* - [F,L]
</IfModule>