web264 字符逃逸

PHP/5.6.40字符逃逸

<?php
/*
# -*- coding: utf-8 -*-
# @Author: h1xa
# @Date:   2020-12-03 02:37:19
# @Last Modified by:   h1xa
# @Last Modified time: 2020-12-03 16:05:38
# @message.php
# @email: h1xa@ctfer.com
# @link: https://ctfer.com
*/
error_reporting(0);
session_start();
class message{
    public $from;
    public $msg;
    public $to;
    public $token='user';
    public function __construct($f,$m,$t){
        $this->from = $f;
        $this->msg = $m;
        $this->to = $t;
    }
}
$f = $_GET['f'];
$m = $_GET['m'];
$t = $_GET['t'];
if(isset($f) && isset($m) && isset($t)){
    $msg = new message($f,$m,$t);
    $umsg = str_replace('fuck', 'loveU', serialize($msg));
    $_SESSION['msg']=base64_encode($umsg);
    echo 'Your message has been sent';
}
highlight_file(__FILE__);

看注释发现 message.php

<?php
/*
# -*- coding: utf-8 -*-
# @Author: h1xa
# @Date:   2020-12-03 15:13:03
# @Last Modified by:   h1xa
# @Last Modified time: 2020-12-03 15:17:17
# @email: h1xa@ctfer.com
# @link: https://ctfer.com
*/
session_start();
highlight_file(__FILE__);
include('flag.php');
class message{
    public $from;
    public $msg;
    public $to;
    public $token='user';
    public function __construct($f,$m,$t){
        $this->from = $f;
        $this->msg = $m;
        $this->to = $t;
    }
}
if(isset($_COOKIE['msg'])){
    $msg = unserialize(base64_decode($_SESSION['msg']));
    if($msg->token=='admin'){
        echo $flag;
    }
}

看注释发现 message.php

<?php
/*
# -*- coding: utf-8 -*-
# @Author: h1xa
# @Date:   2020-12-03 15:13:03
# @Last Modified by:   h1xa
# @Last Modified time: 2020-12-03 15:17:17
# @email: h1xa@ctfer.com
# @link: https://ctfer.com
*/
session_start();
highlight_file(__FILE__);
include('flag.php');
class message{
    public $from;
    public $msg;
    public $to;
    public $token='user';
    public function __construct($f,$m,$t){
        $this->from = $f;
        $this->msg = $m;
        $this->to = $t;
    }
}
if(isset($_COOKIE['msg'])){
    $msg = unserialize(base64_decode($_SESSION['msg']));
    if($msg->token=='admin'){
        echo $flag;
    }
}

一开始没看出和 web262 有啥区别，仔细看了一下发现，反序列化时使用了 session 而不是直接通过 Cookie 接收

做法和 web262中第二种做法一样，虽然不是通过 Cookie 接收，也别忘了了 Cookie 的 msg 字段附加个值，不然不满足

if(isset($_COOKIE['msg'])){

先请求 index.php （这里 poc 不明白怎么构造看一下 web262 第二种做法）

因为 PHP 的 session 是通过 Cookie 里的 PHPSESSID 获取的（不清除参考 web263 session 伪造），所以要记录下来，然后在 message.php 里带上。

然后请求一下 message.php , 别忘了 Cookie 部分

flag
ctfshow{6491abcd-1e5c-489b-b25f-9e941bc5c588}