CVE-2026-25420: MailerLite Auth Bypass Vulnerability

CVE-2026-25420 Overview

CVE-2026-25420 is a Missing Authorization vulnerability (CWE-862) affecting the MailerLite official-mailerlite-sign-up-forms WordPress plugin. This Broken Access Control vulnerability allows attackers to exploit incorrectly configured access control security levels, potentially enabling unauthorized actions within the plugin's functionality.

The vulnerability stems from missing authorization checks in the MailerLite plugin, which could allow unauthenticated or lower-privileged users to perform actions that should be restricted to administrators or authorized users only.

Critical Impact
Attackers may exploit this vulnerability to bypass access controls and perform unauthorized operations on WordPress sites using the affected MailerLite plugin versions.

Affected Products

MailerLite official-mailerlite-sign-up-forms WordPress plugin versions through 1.7.18

Discovery Timeline

2026-02-19 - CVE-2026-25420 published to NVD
2026-02-19 - Last updated in NVD database

Technical Details for CVE-2026-25420

Vulnerability Analysis

This vulnerability represents a Missing Authorization flaw (CWE-862) in the MailerLite WordPress plugin. The core issue is that certain plugin functionality lacks proper authorization checks, allowing users without appropriate permissions to access or modify plugin settings and data.

In WordPress plugin development, authorization checks are typically implemented using capability checks via functions like current_user_can(). When these checks are missing or improperly implemented, it creates an access control gap that attackers can exploit.

The vulnerability enables exploitation of incorrectly configured access control security levels, meaning that the plugin fails to properly verify whether a user has the necessary permissions before executing sensitive operations.

Root Cause

The root cause is the absence of proper authorization verification in one or more plugin endpoints or AJAX handlers. The MailerLite plugin does not adequately validate user capabilities before processing requests, allowing unauthorized access to restricted functionality. This is a common WordPress plugin vulnerability pattern where developers implement authentication (verifying identity) but neglect authorization (verifying permissions).

Attack Vector

An attacker can exploit this vulnerability by directly accessing plugin endpoints or triggering AJAX actions without the required administrative privileges. The attack does not require authentication in some scenarios, depending on the specific functionality exposed. The attacker would craft requests to the vulnerable endpoints, bypassing the intended access control mechanisms.

Since no verified code examples are available, the vulnerability mechanism can be understood as follows: The plugin exposes functionality through WordPress AJAX handlers or REST API endpoints that process requests without first verifying that the requesting user has appropriate capabilities (such as manage_options for administrative actions). This allows any authenticated user, or potentially unauthenticated users, to invoke privileged operations.

For detailed technical information, refer to the Patchstack Vulnerability Report.

Detection Methods for CVE-2026-25420

Indicators of Compromise

Unexpected modifications to MailerLite plugin settings without corresponding administrator activity
Unusual API calls or AJAX requests to MailerLite plugin endpoints from non-administrative user sessions
Sign-up form configurations changed without authorized user intervention
Suspicious entries in WordPress access logs targeting wp-admin/admin-ajax.php with MailerLite-related actions

Detection Strategies

Monitor WordPress access logs for unauthorized access attempts to MailerLite plugin endpoints
Implement web application firewall (WAF) rules to detect and block suspicious requests to WordPress AJAX handlers
Review plugin audit logs for configuration changes made by non-administrative users
Use WordPress security plugins to monitor file integrity and plugin settings changes

Monitoring Recommendations

Enable detailed logging for WordPress AJAX actions related to the MailerLite plugin
Set up alerts for any plugin configuration changes outside of scheduled maintenance windows
Monitor user session activity for privilege escalation attempts
Implement regular security audits of WordPress plugin configurations and user capabilities

How to Mitigate CVE-2026-25420

Immediate Actions Required

Update the MailerLite plugin to a version newer than 1.7.18 if a patched version is available
Review and restrict user roles with access to the WordPress admin panel
Implement a Web Application Firewall (WAF) to filter malicious requests
Temporarily disable the MailerLite plugin if no patch is available and the functionality is not critical

Patch Information

Organizations should check the WordPress plugin repository and the Patchstack Vulnerability Report for availability of a patched version. Update to the latest available version that addresses this vulnerability.

Workarounds

Restrict access to the WordPress admin panel using IP whitelisting at the web server level
Implement additional authentication layers such as HTTP Basic Authentication for wp-admin access
Disable AJAX functionality for unauthenticated users if not required for site functionality
Use WordPress security plugins to add capability checks and monitor plugin behavior

bash

# Example: Restrict wp-admin access by IP in Apache .htaccess
# Place in /wp-admin/.htaccess
<IfModule mod_authz_core.c>
    Require ip 192.168.1.0/24
    Require ip 10.0.0.0/8
</IfModule>

# Example: Restrict admin-ajax.php POST requests in nginx
# Add to server block configuration
location = /wp-admin/admin-ajax.php {
    # Allow GET requests for frontend functionality
    if ($request_method = POST) {
        # Limit to known trusted IPs for admin operations
        allow 192.168.1.0/24;
        deny all;
    }
}