Destoon B2B CMS 20180827版本Getshell漏洞分析利用

时间：2018-09-26 00:02:22人气：次作者：本站作者我要评论

Destoon B2B CMS 20180827版本Getshell漏洞分析利用

漏洞分析

漏洞发生在头像上传处。Destoon中处理头像上传的是 module/member/avatar.inc.php 文件。在会员中心处上传头像时抓包，部分内容如下：

对应avatar.inc.php代码如下：

<?php
defined('IN_DESTOON') or exit('Access Denied');
login();
require DT_ROOT.'/module/'.$module.'/common.inc.php';
require DT_ROOT.'/include/post.func.php';
$avatar = useravatar($_userid, 'large', 0, 2);
switch($action) {
case 'upload':
if(!$_FILES['file']['size']) {
if($DT_PC) dheader('?action=html&reload='.$DT_TIME);
exit('{"error":1,"message":"Error FILE"}');
}
require DT_ROOT.'/include/upload.class.php';
$ext = file_ext($_FILES['file']['name']);
$name = 'avatar'.$_userid.'.'.$ext;
$file = DT_ROOT.'/file/temp/'.$name;
if(is_file($file)) file_del($file);
$upload = new upload($_FILES, 'file/temp/', $name, 'jpg|jpeg|gif|png');
$upload->adduserid = false;
if($upload->save()) {
...
} else {
...
}
break;

这里通过$_FILES['file']依次获取了上传文件扩展名$ext、保存临时文件名$name、保存临时文件完整路径$file变量。之后通过new upload();创立一个upload对象，等到$upload->save()时再将文件真正写入。

upload对象构造函数如下，include/upload.class.php:25：

<?php
class upload {
function __construct($_file, $savepath, $savename = '', $fileformat = '') {
global $DT, $_userid;
foreach($_file as $file) {
$this->file = $file['tmp_name'];
$this->file_name = $file['name'];
$this->file_size = $file['size'];
$this->file_type = $file['type'];
$this->file_error = $file['error'];
}
$this->userid = $_userid;
$this->ext = file_ext($this->file_name);
$this->fileformat = $fileformat ? $fileformat : $DT['uploadtype'];
$this->maxsize = $DT['uploadsize'] ? $DT['uploadsize']*1024 : 2048*1024;
$this->savepath = $savepath;
$this->savename = $savename;
}
}

这里通过foreach($_file as $file)来遍历初始化各项参数。而savepath、savename则是通过__construct($_file, $savepath, $savename = '', $fileformat = '')直接传入参数指定。

因此考虑上传了两个文件，第一个文件名是1.php，第二个文件是1.jpg，只要构造合理的表单上传

$ext = file_ext($_FILES['file']['name']); // `$ext`即为`php`
$name = 'avatar'.$_userid.'.'.$ext; // $name 为 'avatar'.$_userid.'.'php'
$file = DT_ROOT.'/file/temp/'.$name; // $file 即为 www/cesafe/com/cesafe.php

而在upload类中，由于多个文件上传，$this->file、$this->file_name、$this->file_type将foreach在第二次循环中被置为jpg文件。测试如下：

回到avatar.inc.php，当进行文件保存时调用$upload->save()，include/upload.class.php:50:

<?php
class upload {
function save() {
include load('include.lang');
if($this->file_error) return $this->_('Error(21)'.$L['upload_failed'].' ('.$L['upload_error_'.$this->file_error].')');
if($this->maxsize > 0 && $this->file_size > $this->maxsize) return $this->_('Error(22)'.$L['upload_size_limit'].' ('.intval($this->maxsize/1024).'Kb)');
if(!$this->is_allow()) return $this->_('Error(23)'.$L['upload_not_allow']);
$this->set_savepath($this->savepath);
$this->set_savename($this->savename);
if(!is_writable(DT_ROOT.'/'.$this->savepath)) return $this->_('Error(24)'.$L['upload_unwritable']);
if(!is_uploaded_file($this->file)) return $this->_('Error(25)'.$L['upload_failed']);
if(!move_uploaded_file($this->file, DT_ROOT.'/'.$this->saveto)) return $this->_('Error(26)'.$L['upload_failed']);
$this->image = $this->is_image();
if(DT_CHMOD) @chmod(DT_ROOT.'/'.$this->saveto, DT_CHMOD);
return true;
}
}

先经过几个基本参数的检查，然后调用$this->is_allow()来进行安全检查 include/upload.class.php:72：

<?php
function is_allow() {
if(!$this->fileformat) return false;
if(!preg_match("/^(".$this->fileformat.")$/i", $this->ext)) return false;
if(preg_match("/^(php|phtml|php3|php4|jsp|exe|dll|cer|shtml|shtm|asp|asa|aspx|asax|ashx|cgi|fcgi|pl)$/i", $this->ext)) return false;
return true;
}

可以看到这里仅仅对$this->ext进行了检查，如前此时$this->ext为jpg，检查通过。

接着会进行真正的保存。通过$this->set_savepath($this->savepath); $this->set_savename($this->savename);设置了$this->saveto，然后通过move_uploaded_file($this->file, DT_ROOT.'/'.$this->saveto)将file保存到$this->saveto ，注意此时的savepath、savename、saveto均以php为后缀，而$this->file实际指的是第二个jpg文件。