OPEN-BRAIN <= 0.5.0 - Cross-Site Request Forgery

This plan outlines the research and exploitation strategy for CVE-2026-4091 (OPEN-BRAIN <= 0.5.0), a Cross-Site Request Forgery (CSRF) vulnerability that allows for the injection of malicious scripts (Stored XSS).

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1. Vulnerability Summary

The OPEN-BRAIN plugin (versions <= 0.5.0) fails to implement nonce verification in its primary settings management function, func_page_main(). This function handles the processing and saving of plugin configuration. Because it lacks CSRF protection, an attacker can craft a malicious request that, when executed by an authenticated administrator (e.g., via a phishing link), modifies the plugin settings. Furthermore, because these settings are likely rendered back into the admin dashboard without sufficient escaping, this CSRF serves as a vector for Stored Cross-Site Scripting (XSS).

2. Attack Vector Analysis

• Vulnerable Endpoint: wp-admin/admin.php?page=open-brain (inferred slug).
• Vulnerable Function: func_page_main().
• HTTP Method: POST.
• Authentication Level: Administrator (victim).
• Payload Carrying Parameter: Inferred setting fields such as open_brain_id, open_brain_key, or any text-based configuration field processed in the $_POST array within func_page_main().
• Preconditions: An administrator must have an active session and be tricked into submitting a forged request.

3. Code Flow

1. Registration: The plugin registers an admin menu page via add_menu_page() or add_options_page() in the admin_menu hook, pointing to the callback func_page_main.
2. Entry Point: When an admin visits the settings page or submits the form, WordPress invokes func_page_main().
3. Processing:
   • The function checks if $_POST data is present (e.g., if (isset($_POST['submit']))).
   • The Vulnerability: It proceeds to process the input without calling check_admin_referer() or wp_verify_nonce().
4. Sink: The user-supplied input is passed to update_option().
5. XSS Trigger: On subsequent loads of the admin page, the malicious value is retrieved via get_option() and echoed into the HTML, triggering the script.

4. Nonce Acquisition Strategy

No nonce is required. The core of this vulnerability is the complete absence of nonce verification in func_page_main(). An attacker does not need to bypass a nonce check; they simply omit it from the forged request.

5. Exploitation Strategy

The goal is to perform a CSRF that updates a setting with a JavaScript payload, achieving Stored XSS.

Step-by-Step Plan:

1. Discover Parameters: Navigate to the plugin settings page as an admin and identify the exact name attributes of the input fields and the submit button.
2. Identify Target URL: Confirm the admin page URL (e.g., wp-admin/admin.php?page=open-brain).
3. Craft the Payload: Use a simple XSS probe: <script>alert(origin)</script>.
4. Execute Forged Request: Use the http_request tool with administrator cookies to simulate the CSRF attack.

Request Details:

• URL: http://localhost:8080/wp-admin/admin.php?page=open-brain
• Method: POST
• Headers:
  • Content-Type: application/x-www-form-urlencoded
• Body (Example - keys must be verified):
  open_brain_key=<script>alert(origin)</script>&submit=Save+Changes

6. Test Data Setup

1. Plugin Installation: Ensure the OPEN-BRAIN plugin (version <= 0.5.0) is active.
2. Administrative User: A standard WordPress admin user must exist.
3. No Shortcodes Required: Unlike AJAX-based vulnerabilities, this is a standard admin-post CSRF; it does not rely on frontend script localization.

7. Expected Results

• The http_request should return a 302 Redirect or a 200 OK indicating the settings were updated.
• The WordPress database should now contain the XSS payload in the corresponding option.
• Navigating to the plugin settings page in the browser should trigger a JavaScript alert.

8. Verification Steps

After the http_request, verify the impact using wp-cli:

# Check if the option was updated with the payload
wp option get open_brain_key 
# (Replace 'open_brain_key' with the actual option name found during research)

To verify the XSS via the browser:

1. Use browser_navigate to http://localhost:8080/wp-admin/admin.php?page=open-brain.
2. Check for the presence of the script in the page source or use browser_eval to check if a specific global variable was set by your payload.

9. Alternative Approaches

• Action Hook Hijacking: If the plugin uses admin_post_ or admin_ajax_ instead of a direct menu callback, the target URL would be wp-admin/admin-post.php or wp-admin/admin-ajax.php.
• Check for $_REQUEST: If the plugin uses $_REQUEST instead of $_POST, the exploit can be delivered via a simple GET request (e.g., <img src="...">), bypassing some browser-level CSRF protections.
• Blind XSS: If the payload isn't reflected on the settings page, check other admin pages where the plugin settings might be used (e.g., post editors or dashboards).