WordPress plugins make life simpler for site managers, but sometimes they can open doors to trouble. CVE-2023-46203 is one such case—it’s a missing authorization vulnerability found in the popular Just Custom Fields plugin by JustCoded/Alex Prokopenko. Attackers can pry into or mess with parts of your site if you didn’t lock the door in time. Let’s dive deep into this issue: how it happens, what’s at risk, and how attackers can take advantage.

What’s the Problem?

CVE-2023-46203 is a security flaw in the Just Custom Fields plugin—versions up to 3.3.2 (earlier versions are affected, too, but there’s no confirmation of the first vulnerable release). The plugin lets admins add custom fields to posts, pages, and other WordPress objects. The problem is simple yet critical: the plugin doesn’t check if a user is authorized before letting them perform sensitive operations.

This means unauthorized users could trick the system into revealing or changing information that should only be accessible by admins. Exploiting the access control security levels lets attackers escalate their privileges.

Who Discovered It?

The original advisory comes from Wordfence and it’s been published on the National Vulnerability Database (NVD).

Vulnerable Plugin Versions

- Just Custom Fields versions: *from n/a through 3.3.2*

Technical Details

The core of the problem is that the plugin’s AJAX actions (like saving or editing field data via /wp-admin/admin-ajax.php) don’t verify whether the requesting user has the right permissions. In WordPress, every action a user takes is supposed to be checked with a function like current_user_can(). If that gets skipped, any logged-in user—even a subscriber—might be able to call those AJAX functions.

Here’s a simplified example showing what a vulnerable AJAX handler might look like inside the plugin’s PHP code:

add_action('wp_ajax_jcf_save_field', 'jcf_save_field_callback');

function jcf_save_field_callback() {
    // Missing user capability check!
    $post_id = intval($_POST['post_id']);
    $field_data = $_POST['field_data'];

    update_post_meta($post_id, 'custom_field', $field_data);

    echo json_encode(array('status' => 'success'));
    wp_die();
}

Proper code should include a permission check

if ( ! current_user_can('manage_options') ) {
    wp_send_json_error('Unauthorized', 403);
    wp_die();
}

Intercept or craft a request to the plugin’s AJAX handler (e.g., jcf_save_field)

3. Send a POST request with parameters that change or add custom fields data to posts/pages that should be off-limits.

Result: Data for posts or fields can be modified or viewed, depending on how the plugin is used.

*For a practical example, an attacker could change a meta field on any post—even those they don’t own, possibly changing how content appears, injecting code, or tampers with functionality.*

Here’s a cURL command that mimics an attack (for education/research only!)

curl -X POST https://victimsite.com/wp-admin/admin-ajax.php \
  -d "action=jcf_save_field&post_id=123&field_data=hacked" \
  -b "wordpress_logged_in_xxx=USER_SESSION_COOKIE"

Real-World Impact

- Edit posts/pages meta: Attackers could inject unwanted content or scripts.

Fix and Mitigation

Update immediately: Version 3.3.3 of the plugin includes the fix (adding proper authorization checks).
- Just Custom Fields on WordPress.org

Temporary protection (if patching isn’t possible)

- Block access to /wp-admin/admin-ajax.php for non-admin users (with care, as this might break legitimate features).

References

- Wordfence vulnerability report
- NVD CVE-2023-46203 Details
- Plugin Page

Conclusion

CVE-2023-46203 is a classic “forgot to lock the door” vulnerability that’s easy to exploit, if left unpatched. Always ensure plugins are updated, review access controls, and stay aware of security reports. WordPress sites are popular… with hackers, too!

Patch it, secure it, and move on safely!

*Like this write-up? Feel free to share, but always respect the tools you use, and don’t hack without permission.*

Timeline

Published on: 01/02/2025 12:15:11 UTC