Reflected XSS in Cookiebot Administrative Page

Labs Note

A reflected XSS vulnerability has recently been found in the Cookiebot plugin plugin, impacting a user base of over 40k installs. Versions prior to 3.6.1 are susceptible to this attack, which allows hackers to exploit the vulnerability found on administrative pages.

This vulnerability is caused by the manual tabs mechanism, which tries to add a class to the form with the current tab.

<?php if ( isset( $_GET['tab'] ) ) {
     $active_tab = $_GET['tab'];
} else if ( $active_tab == 'unavailable_addons' ) {
     $active_tab = 'unavailable_addons';
} else {
     $active_tab = 'available_addons';
} ?>

// ...

<form method="post" action="options.php" class="<?php echo $active_tab; ?>">

The issue lies in the fact that only two tab types should be present: available_addons or unavailable_addons. These values are never checked, however, and are directly inserted into the form class attribute.

This improper implementation leads to the potential for a reflected cross-site scripting attack which relies on human behavior – such as an administrator visiting a link.
If the website administrator visits an attacker’s specially crafted URL, the bad actor may be able to compromise and take over the website.


  • 2020-03-11: Initial disclosure
  • 2020-03-12: Version 3.6.1 released

Mitigation Steps:

Websites using Cookiebot versions lower than 3.6.1 should update their plugins to the latest patch immediately to mitigate risk. As always, customers using our WAF are protected from this issue with our virtual patching technology.

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