Research Plan: CVE-2026-27379 - NextScripts: Social Networks Auto-Poster (SNAP) PHP Object Injection

1. Vulnerability Summary

The NextScripts: Social Networks Auto-Poster (SNAP) plugin for WordPress (versions <= 4.4.7) is vulnerable to PHP Object Injection due to the insecure use of the unserialize() function on user-controllable input. Specifically, the plugin processes settings and post-related data via AJAX handlers that do not adequately verify the user's capabilities (allowing Contributor+ access) or sanitize the input before deserialization. An attacker can submit a base64-encoded, serialized PHP object to trigger the vulnerability. While no built-in POP (Property-Oriented Programming) chain is identified in the plugin itself, this vulnerability can be leveraged if other plugins or themes on the site provide a suitable chain for Remote Code Execution (RCE) or arbitrary file deletion.

2. Attack Vector Analysis

• Endpoint: /wp-admin/admin-ajax.php
• AJAX Action: nxs_snap_aj (inferred from common SNAP AJAX routing)
• Vulnerable Parameter: nxs_mq_data or nxs_data (inferred based on plugin history)
• Authentication: Contributor-level session required.
• Preconditions:
  1. The plugin must be active.
  2. A valid WordPress nonce for the SNAP AJAX action must be obtained.
  3. The attacker must have a user account with at least contributor privileges.

3. Code Flow (Inferred)

1. Entry Point: The plugin registers a central AJAX handler:
   add_action('wp_ajax_nxs_snap_aj', 'nxs_snap_aj_callback'); (or similar registration in nxs-snap.php).
2. Lack of Capability Check: The callback function nxs_snap_aj_callback (located in inc/nxs-functions.php or classes/class-nxs-main.php) checks for a valid nonce but fails to check for manage_options capability, allowing any logged-in user to reach the logic.
3. Data Retrieval: The function retrieves a POST parameter (likely nxs_mq_data or nxs_data).
4. Decoding: The input is often passed through stripslashes() and base64_decode().
5. Vulnerable Sink: The decoded string is passed directly to unserialize().

   // Inferred vulnerable code pattern
   if (isset($_POST['nxs_data'])) {
       $raw_data = $_POST['nxs_data'];
       $decoded = base64_decode($raw_data);
       $data = unserialize($decoded); // PHP Object Injection point
   }
   

4. Nonce Acquisition Strategy

The SNAP plugin localizes its AJAX configuration, including the nonce, to the WordPress admin dashboard.

1. Identify Shortcode/Page: SNAP's scripts are typically enqueued on its settings pages, but basic AJAX vars are often available on the main Dashboard or Post Editor for authorized users.
2. Target Variable: The plugin uses a localized JavaScript object, typically named nxs_script_vars or nxs_snap_ajax.
3. Action String: The nonce is usually generated for the action nxs_snap_aj.
4. Strategy:
   • Log in as a Contributor.
   • Navigate to /wp-admin/index.php (Dashboard).
   • Execute browser_eval to extract the nonce.
   • JS Logic: window.nxs_script_vars?.nxs_snap_ajax_nonce or window.nxs_snap_ajax?.nonce.

5. Exploitation Strategy

Step 1: Authentication

Log in to the WordPress target using Contributor credentials.

Step 2: Nonce Extraction

Use the browser_navigate and browser_eval tools to grab the nonce.

• Navigate: https://<target>/wp-admin/index.php
• Eval: nxs_script_vars.nxs_snap_ajax_nonce (Verify the exact key in the page source).

Step 3: Payload Preparation

Create a serialized PHP object. Since no specific POP chain is known, we will use a simple "dummy" object to verify the injection point (e.g., a non-existent class which will trigger a PHP notice if logging is enabled).

• Object: O:20:"NXS_Exploit_Verified":0:{}
• Base64 Payload: TzoyMDoiTlhTX0V4cGxvaXRfVmVyaWZpZWQiOjA6e30=

Step 4: Execution

Submit the payload via http_request.

• URL: https://<target>/wp-admin/admin-ajax.php
• Method: POST
• Headers: Content-Type: application/x-www-form-urlencoded
• Body:

  action=nxs_snap_aj&nxs_snap_ajax_nonce=[NONCE]&nxs_data=TzoyMDoiTlhTX0V4cGxvaXRfVmVyaWZpZWQiOjA6e30=
  

6. Test Data Setup

1. User: Create a user with the contributor role.
2. Plugin Settings: Ensure SNAP is active. Default settings are sufficient.
3. Enable Logging: To verify the injection, enable WP_DEBUG and WP_DEBUG_LOG in wp-config.php.

7. Expected Results

• The server should return a 200 OK response (unless the deserialization causes a fatal error).
• If WP_DEBUG_LOG is enabled, look for an entry: PHP Fatal error: unserialize(): Drawing of 'NXS_Exploit_Verified' failed or Class 'NXS_Exploit_Verified' not found.
• If using a known POP chain (e.g., from another plugin like Elementor or a core class like WP_Theme for older versions), the side effect of that chain (file write, etc.) should be observable.

8. Verification Steps

After sending the request, check the WordPress debug log:

# Check the debug log for evidence of deserialization attempt
cat /var/www/html/wp-content/debug.log | grep "NXS_Exploit_Verified"

Verify that the nxs_snap_aj action is indeed reachable by a contributor:

# Check if the handler performs capability checks
grep -r "function nxs_snap_aj_callback" /var/www/html/wp-content/plugins/social-networks-auto-poster-facebook-twitter-g/

9. Alternative Approaches

If nxs_data is not the correct parameter:

1. Search the source for all occurrences of unserialize(:
   grep -rn "unserialize(" /var/www/html/wp-content/plugins/social-networks-auto-poster-facebook-twitter-g/
2. If the input is not Base64, try URL-encoded raw serialized data.
3. Some SNAP versions use maybe_unserialize(). Check if parameters passed to maybe_unserialize originate from $_POST.
4. Check for other AJAX actions: nxs_repost_aj, nxs_testPost, or nxs_getLog. These often share the same routing logic.