Context IS Advisory - MS08-39 OWA XSS

===============================ADVISORY===============================

Systems Affected: Microsoft Outlook Web Access 2003 and 2007
(Exchange Server 2003 SP2, Exchange Server 2007,
Exchange Server 2007 SP1)
Severity: High
Category: Cross Site Scripting, Cross Site Request Forgery
Author: Context Information Security Ltd
Reported to vendor: 10th January 2008
Advisory Issued: 10th July 2008

===============================ADVISORY===============================

Description

Several Cross Site Scripting vulnerabilities were found in within Outlook Web Access (OWA)
2003/2007. An attacker can craft a malicious email which will trigger within a user's browser.
Different version of OWA and different clients (Light and Premium) have different attack vectors
which can result in an attacker gaining persistent control over a victim's use of Outlook Web
Access. An attacker would have full control and access to the victims e-mail account. This control
could be further abused by utilising techniques such as JavaScript root-kits or web worms.

Analysis

An attacker can craft a malicious email which contains the attack strings to compromise an OWA
client. The user would only need to view the email to be victim to the XSS attack. Furthermore,
persistent XSS can be gained by changing certain values within OWA to a particular XSS attack string.
This string (consisting of HTML/JavaScript) is subsequently injected into any page which uses this
value, including "new email", "reply email" (for OWA 2003) and most pages (for OWA 2007). Logging
out of the application and back in will not clear the attack. Furthermore, the attack can be
propagated by using the control over the OWA client to email the attack link to all users in the
victim's inbox/contacts.

At this point the attack would spread as a XSS worm (albeit one requiring the user to view the
incoming email). This could potentially affect all users of the OWA application.

Technologies Affected

Microsoft Exchange Server 2003
Microsoft Exchange Server 2007
Microsoft Exchange Server 2007 SP1

Vendor Response

On 9th July 2008, Microsoft issued a security bulletin MS08-039 and an associated patch for Exchange
Server 2003 and Exchange Server 2007 SP1

Patches are available from:

http://www.microsoft.com/technet/security/bulletin/ms08-039.mspx

Context would recommend that these patches be installed as soon as practical to all Exchange Servers
providing OWA functionality.

CVE

This issue has been assigned CVE numbers CVE-2008-2247 and CVE-2008-2248.

Disclosure Timeline

10 January 2008 - Initial Discovery and vendor notification.
14th January 2008 - Vendor response requesting further details.
14th March 2008 - Vendor response requesting PoC. PoC provided.
9th July 2008 - Vendor advisory release.
10th July 2008 - Context Information Security Ltd advisory release.

Credits

Michael Jordon of Context Information Security Ltd

About Context Information Security

Context Information Security Limited is a specialist information security consultancy based in
London and Frankfurt. Context promotes the holistic approach to information security and helps
clients to identify, assess and control their exposure to risk within the fields of IT, telephony and
physical security. Context employs experienced information security professionals who are
subject-matter experts in their various technical specialism's. Context works extensively within the
finance, legal, defence and government sectors, delivering high-end information security projects to
organisations for which security is a priority.

Web: www.contextis.co.uk
Email: [email protected]