Hunting for Vulnerabilities in WordPress Plugins

WordPress powers over 40% of the web, making it a prime target for attackers. Many vulnerabilities stem from insecure plugins, which can lead to SQL injection, remote code execution, authentication bypasses, and more. In this post, we’ll break down a systematic approach to finding and analyzing security flaws in WordPress plugins.

Finding a Target Plugin

Before hunting for vulnerabilities, you need to pick a target. Good candidates include:

• Popular Plugins – A vulnerability in a widely used plugin has a greater impact.
• Outdated Plugins – Abandoned or rarely updated plugins may have unpatched issues.
• Recently Updated Plugins – Changes in code can introduce new vulnerabilities.

Where to Find Plugins?

• WordPress Plugin Directory
• CodeCanyon (Premium plugins)
• GitHub repositories (Often open-source plugins)

Checking for Known Vulnerabilities

Before diving into code, check if the plugin has already been reported for vulnerabilities:

• WPScan Vulnerability Database
• Exploit-DB
• CVE Details
• Packet Storm

Use WPScan to scan for known vulnerabilities:

wpscan --url https://target.com --api-token YOUR_WPSCAN_API_KEY

Finding the Source Code of Plugin Endpoints

If a plugin is already installed on a WordPress site, you can find its source code in the following directory:

wp-content/plugins/

Navigate to a specific plugin:

cd wp-content/plugins/plugin-name/

You’ll find PHP files, JavaScript, and other assets that make up the plugin.

Plugins usually have the following structure:

plugin-name/
│── plugin-name.php  # Main plugin file
│── includes/
│── admin/
│── public/
│── templates/
│── assets/

Finding AJAX Endpoints

WordPress plugins often define AJAX handlers via admin-ajax.php. Search for:

grep -R "add_action('wp_ajax_" .

Example output:

add_action('wp_ajax_custom_action', 'custom_ajax_handler');
add_action('wp_ajax_nopriv_custom_action', 'custom_ajax_handler');

• wp_ajax_ → Requires authentication (admin access).
• wp_ajax_nopriv_ → Accessible to unauthenticated users (higher attack surface).

Find the function definition:

grep -R "function custom_ajax_handler" .

Finding REST API Endpoints

Many plugins use the WordPress REST API (wp-json). Locate them with:

grep -R "register_rest_route(" .

Example:

register_rest_route('plugin/v1', '/data/', array(
    'methods' => 'GET',
    'callback' => 'get_plugin_data',
    'permission_callback' => '__return_true',
));

• The route is /wp-json/plugin/v1/data/
• The callback function (get_plugin_data) processes the request.
• No authentication? 🚨 Potential security risk!

Find the function:

grep -R "function get_plugin_data" .

Finding Custom URL Parameters

Search for direct user input handling:

grep -R "\$_GET" .
grep -R "\$_POST" .
grep -R "\$_REQUEST" .

Look for SQL queries, unsafe eval(), or file inclusion.

Finding File Upload Handlers

Check if file uploads are unrestricted:

grep -R "move_uploaded_file" .
grep -R "wp_handle_upload" .

Example:

if(isset($_FILES['file'])){
    move_uploaded_file($_FILES['file']['tmp_name'], 'uploads/'.$_FILES['file']['name']);
}

If there’s no file type validation, attackers may upload PHP shells.

Finding Authentication & Privilege Checks

Identify functions that verify user roles:

grep -R "current_user_can" .
grep -R "wp_verify_nonce" .

Missing these checks? 🚨 Potential privilege escalation vulnerability.

Reporting & Responsible Disclosure

If you discover a 0-day vulnerability, report it responsibly:

• Contact the plugin developer (found in the plugin page).
• Report to the WordPress Security Team at [email protected].
• Submit to bug bounty platforms if applicable.

If the vulnerability is patched and public, consider writing a detailed blog post (like this one 😏).

Conclusion

Hunting for WordPress plugin vulnerabilities requires a mix of static analysis, dynamic testing, and fuzzing. By understanding how plugins interact with WordPress, you can uncover hidden security flaws and improve web security.

Happy hunting! 🚀🔍