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Date: Wed, 13 Dec 2017 12:25:57 +0200
From: Maor Shwartz <maors@...ondsecurity.com>
To: fulldisclosure@...lists.org
Cc: SecuriTeam Secure Disclosure <ssd@...ondsecurity.com>
Subject: [FD] SSD Advisory – vBulletin routestring Unauthenticated Remote Code Execution

SSD Advisory – vBulletin routestring Unauthenticated Remote Code Execution

Full report: https://blogs.securiteam.com/index.php/archives/3569
Twitter: @SecuriTeam_SSD
Weibo: SecuriTeam_SSD

Vulnerability Summary
The following advisory describes a unauthenticated file inclusion
vulnerability that leads to remote code execution found in vBulletin
version 5.

vBulletin, also known as vB, is a widespread proprietary Internet forum
software package developed by vBulletin Solutions, Inc., based on PHP and
MySQL database server. vBulletin powers many of the largest social sites on
the web, with over 100,000 sites built on it, including Fortune 500 and
Alexa Top 1M companies websites and forums. According to the latest
W3Techs1 statistics, vBulletin version 4 holds more than 55% of the
vBulletin market share, while version 3 and 5 divide the remaining
percentage

Credit
An independent security researcher has reported this vulnerability to
Beyond Security’s SecuriTeam Secure Disclosure program

Vendor response
We tried to contact vBulletin since November 21 2017, repeated attempts to
establish contact went unanswered. At this time there is no solution or
workaround for these vulnerabilities.


Vulnerability details
vBulletin contains a vulnerability that can allow a remote attacker to
include any file from the vBulletin server and execute arbitrary PHP code.

An unauthenticated user is able to send a GET request to /index.php which
can then trigger the file inclusion vulnerability with parameter
routestring=.

The request allows an attacker to create a crafted request to Vbulletin
server installed on Windows OS and include any file on the web server.

Listing of /index.php:

===

/* 48 */ $app = vB5_Frontend_Application::init('config.php');

/* 49 */ //todo, move this back so we can catch notices in the startup
code. For now, we can set the value in the php.ini

/* 50 */ //file to catch these situations.

/* 51 */ // We report all errors here because we have to make Application
Notice free

/* 52 */ error_reporting(E_ALL | E_STRICT);

/* 53 */

/* 54 */ $config = vB5_Config::instance();

/* 55 */ if (!$config->report_all_php_errors) {

/* 56 */  // Note that E_STRICT became part of E_ALL in PHP 5.4

/* 57 */  error_reporting(E_ALL & ~(E_NOTICE | E_STRICT));

/* 58 */ }

/* 59 */

/* 60 */ $routing = $app->getRouter();

/* 61 */ $method = $routing->getAction();

/* 62 */ $template = $routing->getTemplate();

/* 63 */ $class = $routing->getControllerClass();

/* 64 */

/* 65 */ if (!class_exists($class))

/* 66 */ {

/* 67 */  // @todo - this needs a proper error message

/* 68 */  die("Couldn't find controller file for $class");

/* 69 */ }

/* 70 */

/* 71 */ vB5_Frontend_ExplainQueries::initialize();

/* 72 */ $c = new $class($template);

/* 73 */

/* 74 */ call_user_func_array(array(&$c, $method),
$routing->getArguments());

/* 75 */

/* 76 */ vB5_Frontend_ExplainQueries::finish();

===

Let’s take a closer look on vB5_Frontend_Application::init() – Listing of
/includes/vb5/frontend/application.php:

===

/* 15 */   public static function init($configFile)

/* 16 */    {

/* 17 */       parent::init($configFile);

/* 18 */

/* 19 */       self::$instance = new vB5_Frontend_Application();

/* 20 */       self::$instance->router = new vB5_Frontend_Routing();

/* 21 */       self::$instance->router->setRoutes();

/* ... */

===

We can see that setRoutes() is called:

Listing of /includes/vb5/frontend/routing.php:

===

/* 47 */      public function setRoutes()

/* 48 */      {

/* 49 */         $this->processQueryString();

/* 50 */

/* 51 */         //TODO: this is a very basic and straight forward way of
parsing the URI, we need to improve it

/* 52 */         //$path = isset($_SERVER['PATH_INFO']) ?
$_SERVER['PATH_INFO'] : '';

/* 53 */

/* 54 */         if (isset($_GET['routestring']))

/* 55 */         {

/* 56 */            $path = $_GET['routestring'];

/* ... */

/* 73 */         }

/* 74 */

/* 75 */         if (strlen($path) AND $path{0} == '/')

/* 76 */         {

/* 77 */            $path = substr($path, 1);

/* 78 */         }

/* 79 */

/* 80 */         //If there is an invalid image, js, or css request we wind
up here. We can't process any of them

/* 81 */         if (strlen($path) > 2 )

/* 82 */         {

/* 83 */            $ext = strtolower(substr($path, -4)) ;

/* 84 */            if (($ext == /* 47 */      public function setRoutes()


/* 48 */      {

/* 49 */         $this->processQueryString();

/* 50 */

/* 51 */         //TODO: this is a very basic and straight forward way of
parsing the URI, we need to improve it

/* 52 */         //$path = isset($_SERVER['PATH_INFO']) ?
$_SERVER['PATH_INFO'] : '';

/* 53 */

/* 54 */         if (isset($_GET['routestring']))

/* 55 */         {

/* 56 */            $path = $_GET['routestring'];

/* ... */

/* 73 */         }

/* 74 */

/* 75 */         if (strlen($path) AND $path{0} == '/')

/* 76 */         {

/* 77 */            $path = substr($path, 1);

/* 78 */         }

/* 79 */

/* 80 */         //If there is an invalid image, js, or css request we wind
up here. We can't process any of them

/* 81 */         if (strlen($path) > 2 )

/* 82 */         {

/* 83 */            $ext = strtolower(substr($path, -4)) ;

/* 84 */            if (($ext == '.gif') OR ($ext == '.png') OR ($ext ==
'.jpg') OR ($ext == '.css')

/* 85 */               OR (strtolower(substr($path, -3)) == '.js') )

/* 86 */            {

/* 87 */               header("HTTP/1.0 404 Not Found");

/* 88 */               die('');

/* 89 */            }

/* 90 */         }

/* 91 */

/* 92 */         try

/* 93 */         {

/* 94 */            $message = ''; // Start with no error.

/* 95 */            $route =
Api_InterfaceAbstract::instance()->callApi('route', 'getRoute',
array('pathInfo' => $path, 'queryString' => $_SERVER['QUERY_STRING']));


/* 96 */         }

/* 97 */         catch (Exception $e)

/* 98 */         {

/* ... */

/* 106 */         }

/* ... */

/* 127 */         if (!empty($route))

/* 128 */         {

/* ... */

/* 188 */         }

/* 189 */         else

/* 190 */         {

/* 191 */            // if no route was matched, try to parse route as
/controller/method

/* 192 */            $stripped_path = preg_replace('/[^a-z0-9\/-_.]+/i',
'', trim(strval($path), '/'));

/* ... */

/* 229 */         }

/* 230 */

/* 231 */         //this could be a legacy file that we need to proxy.  The
relay controller will handle

/* 232 */         //cases where this is not a valid file.  Only handle
files in the "root directory".  We'll

/* 233 */         //handle deeper paths via more standard routes.

/* 234 */         if (strpos($path, '/') === false)

/* 235 */         {

/* 236 */            $this->controller = 'relay';

/* 237 */            $this->action = 'legacy';

/* 238 */            $this->template = '';

/* 239 */            $this->arguments = array($path);

/* 240 */            $this->queryParameters = array();

/* 241 */            return;

/* 242 */         }

/* 243 */

/* 244 */         vB5_ApplicationAbstract::checkState();

/* 245 */

/* 246 */         throw new vB5_Exception_404("invalid_page_url");

/* 247 */      }   ) )

/* 86 */            {

/* 87 */               header("HTTP/1.0 404 Not Found");

/* 88 */               die('');

/* 89 */            }

/* 90 */         }

/* 92 */         try

/* 93 */         {

/* 94 */            $message = ''; // Start with no error.

/* 95 */            $route =
Api_InterfaceAbstract::instance()->callApi('route', 'getRoute',
array('pathInfo' => $path, 'queryString' => $_SERVER['QUERY_STRING']));


/* 96 */         }

/* 97 */         catch (Exception $e)

/* 98 */         {

/* ... */

/* 106 */         }

/* ... */

/* 127 */         if (!empty($route))

/* 128 */         {

/* ... */

/* 188 */         }

/* 189 */         else

/* 190 */         {

/* 191 */            // if no route was matched, try to parse route as
/controller/method

/* 192 */            $stripped_path = preg_replace('/[^a-z0-9\/-_.]+/i',
'', trim(strval($path), '/'));

/* ... */

/* 229 */         }

/* 230 */

/* 231 */         //this could be a legacy file that we need to proxy.  The
relay controller will handle

/* 232 */         //cases where this is not a valid file.  Only handle
files in the "root directory".  We'll

/* 233 */         //handle deeper paths via more standard routes.

/* 234 */         if (strpos($path, '/') === false)

/* 235 */         {

/* 236 */            $this->controller = 'relay';

/* 237 */            $this->action = 'legacy';

/* 238 */            $this->template = '';

/* 239 */            $this->arguments = array($path);

/* 240 */            $this->queryParameters = array();

/* 241 */            return;

/* 242 */         }

/* … */

===

So if our routestring does not end with ‘.gif’, ‘.png’, ‘.jpg’, ‘.css’ or
‘.js’ and does not contain ‘/’ char vBulletin will call legacy() method
from vB5_Frontend_Controller_Relay –
/includes/vb5/frontend/controller/relay.php:

===

/* 63 */   public function legacy($file)

/* 64 */   {

/* 65 */      $api = Api_InterfaceAbstract::instance();

/* 66 */      $api->relay($file);

/* 67 */   }

===

If we will check relay() from Api_Interface_Collapsed class –
/include/api/interface/collapsed.php:

===

/* 117 */   public function relay($file)

/* 118 */   {

/* 119 */      $filePath = vB5_Config::instance()->core_path . '/' . $file;

/* 120 */

/* 121 */      if ($file AND file_exists($filePath))

/* 122 */      {

/* 123 */         //hack because the admincp/modcp files won't return so
the remaining processing in

/* 124 */         //index.php won't take place.  If we better integrate the
admincp into the

/* 125 */         //frontend, we can (and should) remove this.

/* 126 */
vB_Shutdown::instance()->add(array('vB5_Frontend_ExplainQueries',
'finish'));

/* 127 */         require_once($filePath);

/* 128 */      }

/* ... */

===

As we could see an attacker is not able to use ‘/’ in the $file so he
cannot change current directory on Linux. But for Windows he can use ‘\’ as
path delimiter and is able to specify any desired file (he can use ‘\..\’
trick as well) and it will be included by php.


If we want to include file with extension like ‘.gif’, ‘.png’, ‘.jpg’,
‘.css’ or ‘.js’ we will need to bypass the mentioned check in setRoutes()
method. This can be easily done by adding dot (‘.’) or space (‘%20’) to the
filename.



--
Thanks
Maor Shwartz
Beyond Security
GPG Key ID: 6D273779F52A9FC2

Download attachment "SSD Advisory – vBulletin routestring Unauthenticated Remote Code Execution.pdf" of type "application/pdf" (200826 bytes)


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