diff --git a/public/main/inc/lib/formvalidator/FormValidator.class.php b/public/main/inc/lib/formvalidator/FormValidator.class.php
index 4570d43ebb5..94ad843301f 100644
--- a/public/main/inc/lib/formvalidator/FormValidator.class.php
+++ b/public/main/inc/lib/formvalidator/FormValidator.class.php
@@ -2,6 +2,8 @@
 
 /* For licensing terms, see /license.txt */
 
+use Chamilo\CoreBundle\Component\HTMLPurifier\Filter\RemoveOnAttributes;
+
 /**
  * Class FormValidator
  * create/manipulate/validate user input.
diff --git a/src/CoreBundle/Component/HTMLPurifier/Filter/RemoveOnAttributes.php b/src/CoreBundle/Component/HTMLPurifier/Filter/RemoveOnAttributes.php
new file mode 100644
index 00000000000..93589f4970b
--- /dev/null
+++ b/src/CoreBundle/Component/HTMLPurifier/Filter/RemoveOnAttributes.php
@@ -0,0 +1,29 @@
+<?php
+
+/* For licensing terms, see /license.txt */
+
+declare(strict_types=1);
+
+namespace Chamilo\CoreBundle\Component\HTMLPurifier\Filter;
+
+use HTMLPurifier_Filter;
+
+class RemoveOnAttributes extends HTMLPurifier_Filter
+{
+    /**
+     * @var string
+     */
+    public $name = 'RemoveOnAttributes';
+
+    public function preFilter($html, $config, $context): string
+    {
+        return self::filter($html);
+    }
+
+    public static function filter($html): string
+    {
+        $pattern = '/\s*on\w+=(?:"[^"]*"|\'[^\']*\'|[^\s>]+)/i';
+
+        return preg_replace($pattern, '', $html);
+    }
+}