CVE-2026-0674: Campaign Monitor WordPress Auth Bypass

CVE-2026-0674 Overview

A Missing Authorization vulnerability has been identified in the Campaign Monitor for WordPress plugin (forms-for-campaign-monitor). This broken access control flaw allows attackers to exploit incorrectly configured access control security levels, potentially enabling unauthorized access to plugin functionality that should be restricted to authenticated or privileged users.

Critical Impact

Attackers can bypass authorization checks to access restricted plugin functionality, potentially leading to unauthorized data access or manipulation of Campaign Monitor form configurations.

Affected Products

• Campaign Monitor for WordPress plugin versions through 2.9.0
• WordPress installations using the forms-for-campaign-monitor plugin

Discovery Timeline

• January 8, 2026 - CVE-2026-0674 published to NVD
• January 8, 2026 - Last updated in NVD database

Technical Details for CVE-2026-0674

Vulnerability Analysis

This vulnerability stems from CWE-862 (Missing Authorization), a security weakness where the application fails to perform authorization checks when a user attempts to access a resource or perform an action. In the context of WordPress plugins, this typically manifests when AJAX handlers, REST API endpoints, or administrative functions lack proper capability checks using WordPress functions like current_user_can().

The Campaign Monitor for WordPress plugin provides form integration functionality, and the missing authorization allows users without proper permissions to access functionality that should be restricted. This type of broken access control vulnerability is particularly dangerous in WordPress environments where plugins often handle sensitive configuration data and integrate with external services like Campaign Monitor's email marketing platform.

Root Cause

The root cause is the absence of proper authorization verification in one or more plugin functions. WordPress plugins must implement capability checks to ensure that only users with appropriate roles and permissions can execute sensitive operations. When these checks are missing, any authenticated user—or in some cases unauthenticated visitors—can invoke protected functionality.

Attack Vector

An attacker can exploit this vulnerability by directly calling plugin endpoints or functions without having the required WordPress user capabilities. This could involve:

1. Crafting direct requests to AJAX action handlers that lack check_ajax_referer() or capability verification
2. Accessing REST API endpoints without proper permission callbacks
3. Invoking administrative functions through predictable URL patterns or form submissions

The vulnerability allows exploitation of incorrectly configured access control security levels, meaning the attack surface depends on which specific plugin functions lack proper authorization checks.

Detection Methods for CVE-2026-0674

Indicators of Compromise

• Unexpected modifications to Campaign Monitor form configurations or settings
• Unusual AJAX requests to WordPress admin-ajax.php referencing the forms-for-campaign-monitor plugin
• Access logs showing unauthorized users accessing plugin-specific endpoints
• Unexpected changes to email list integrations or form submission handlers

Detection Strategies

• Monitor WordPress access logs for suspicious requests to admin-ajax.php with Campaign Monitor plugin action parameters
• Implement Web Application Firewall (WAF) rules to detect unauthorized access attempts to WordPress plugin endpoints
• Review audit logs for configuration changes made by users without administrative privileges
• Deploy endpoint detection to identify unusual plugin behavior patterns

Monitoring Recommendations

• Enable WordPress debug logging to capture unauthorized access attempts
• Configure alerting for modifications to plugin settings by non-administrative users
• Monitor for bulk or automated requests targeting plugin AJAX handlers
• Implement real-time monitoring of WordPress wp_options table changes related to the plugin

How to Mitigate CVE-2026-0674

Immediate Actions Required

• Update the Campaign Monitor for WordPress plugin to a patched version when available
• Review and restrict user roles with access to form management functionality
• Consider temporarily deactivating the plugin if it is not critical to operations
• Audit existing Campaign Monitor configurations for unauthorized changes
• Implement additional access controls at the web server or WAF level

Patch Information

The vulnerability affects Campaign Monitor for WordPress versions through 2.9.0. Users should check the Patchstack Vulnerability Database Entry for the latest patch status and upgrade to a version that addresses this security issue when available.

Workarounds

• Restrict access to the WordPress admin area using IP whitelisting or VPN requirements
• Implement a WordPress security plugin with capability to add additional authorization checks
• Use .htaccess rules to limit access to admin-ajax.php from trusted sources only
• Consider implementing two-factor authentication for all WordPress user accounts

# Example .htaccess restriction for admin-ajax.php (use with caution)
<Files admin-ajax.php>
    Order deny,allow
    Deny from all
    Allow from 192.168.1.0/24
    # Add your trusted IP ranges above
</Files>