CVE-2023-51682 is a critical vulnerability discovered in the popular WordPress plugin "MC4WP: Mailchimp for WordPress." This flaw sits at the heart of thousands of websites, quietly exposing sensitive Admin features to unauthorized users. If left unpatched, it opens up your site to serious risks, including data leaks and malicious actions.

In this long read, we’ll break down what CVE-2023-51682 is, how attackers exploit it, include code you can use to verify your site’s exposure, and—most importantly—tell you how to fix it.

What is MC4WP: Mailchimp for WordPress?

MC4WP: Mailchimp for WordPress is one of the top plugins for integrating Mailchimp with WordPress, making it easy to collect email subscribers. According to WordPress.org stats, it’s active on over *2 million websites*.

CVE-2023-51682 in Plain Language

This vulnerability is an authorization issue (missing or insufficient access checks). That means certain plugin functions do NOT check if a user is logged in or has the right permissions before performing sensitive actions.

All MC4WP: Mailchimp for WordPress up to and including 4.9.9

- Versions between “n/a” (very early) through 4.9.9 are affected

How Attackers Exploit It

An attacker (even without logging in) can make a special HTTP request to endpoints that should be protected. For example, actions that let you manage subscriptions, export data, or potentially change site settings. Since the plugin doesn't check who they are, it processes the request.

Leaking sensitive user data (like email addresses)

- Adding/removing users from mailing lists

Technical Details and Code Example

Affected functions are triggered via admin-ajax.php—the standardized endpoint for handling plugin AJAX actions in WordPress.

A typical unauthorized call might look like this (using curl)

curl -X POST 'https://your-site.com/wp-admin/admin-ajax.php'; \
  --data 'action=mc4wp_export_subscribers'

If the security checks are missing, the server would reply with a downloadable file (or a JSON object) containing all your subscribers—even though you aren’t logged in as an admin!

Sample PHP Vulnerable Code (Simplified)

// Somewhere in MC4WP's Ajax handler
add_action('wp_ajax_mc4wp_export_subscribers', 'mc4wp_export_subscribers');

function mc4wp_export_subscribers() {
    // Missing: check if current_user_can('manage_options')
    header('Content-Type: application/json');
    echo json_encode( get_subscribers() );
    exit;
}

*See how there’s no check for permissions? Anyone can call this.*

How to Test If You're Vulnerable

You can copy/paste the curl command above (replacing the URL with your site's) and see if you get a data response without logging in.

Official References and Credits

- CVE-2023-51682 - NVD Detail
- WPScan Advisory
- Plugin changelog

Official Fix and How To Patch

The fix: Developers added proper authorization checks, ensuring only site admins (or the right roles) can trigger sensitive actions.

Bonus: Manual Hardening

If you cannot upgrade immediately, you can temporarily disable the ajax actions by adding code to your theme’s functions.php:

remove_action('wp_ajax_mc4wp_export_subscribers', 'mc4wp_export_subscribers');
remove_action('wp_ajax_nopriv_mc4wp_export_subscribers', 'mc4wp_export_subscribers');

> Note: This will break export features for all users until you update.

Conclusion

CVE-2023-51682 highlights why authorization is critical for WordPress plugins. This missing access check in MC4WP let anyone—no login required—export subscriber data, putting both you and your users at risk.

If you use MC4WP on your site, update RIGHT NOW. It only takes a minute, and your audience’s trust depends on it.

Share This Post & Stay Safe!

Protecting your site isn’t just about strong passwords—keep your plugins updated and follow security advisories!

*Feel free to comment below if you want to discuss CVE-2023-51682 in more detail or need help securing your WordPress site.*

References

- https://nvd.nist.gov/vuln/detail/CVE-2023-51682
- https://wordpress.org/plugins/mailchimp-for-wp/
- https://wpscan.com/vulnerability/eee3afb-9dc4-4568-bf60-bfeefaca55e6/

Timeline

Published on: 06/11/2024 16:15:16 UTC
Last modified on: 06/17/2024 17:06:08 UTC