Microsoft Security Bulletin MS08-056 - Moderate Vulnerability in Microsoft Office Could Allow Information Disclosure (957699)

Microsoft Security Bulletin MS08-056 - Moderate
Vulnerability in Microsoft Office Could Allow Information Disclosure (957699)
Published: October 14, 2008

Version: 1.0
General Information
Executive Summary

This security update resolves a privately reported vulnerability in Microsoft Office. The vulnerability could allow information disclosure if a user clicks a specially crafted CDO URL. An attacker who successfully exploited this vulnerability could inject a client side script in the user's browser that could spoof content, disclose information, or take any action that the user could take on the affected Web site.

This security update is rated Moderate for supported editions of Microsoft Office XP.

The security update addresses the vulnerability by unregistering the CDO protocol. For more information about the vulnerability, see the Frequently Asked Questions (FAQ) subsection for the specific vulnerability entry under the next section, Vulnerability Information.

Recommendation. Microsoft recommends that customers consider applying the security update.

Known Issues. None
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Affected and Non-Affected Software

The following software have been tested to determine which versions or editions are affected. Other versions or editions are either past their support life cycle or are not affected. To determine the support life cycle for your software version or edition, visit Microsoft Support Lifecycle.

Affected Software
Office Suite and Other Software Maximum Security Impact Aggregate Severity Rating Bulletins Replaced by this Update

Microsoft Office XP Service Pack 3
(KB956464)

Information Disclosure

Moderate

None

Non-Affected Software
Office and Other Software

Microsoft Office 2000 Service Pack 3

Microsoft Office 2003 Service Pack 2

Microsoft Office 2003 Service Pack 3

2007 Microsoft Office System

2007 Microsoft Office System Service Pack 1

Microsoft Office Excel/PowerPoint/Word Viewer 2003

Excel/PowerPoint/Word Viewer 2003 Service Pack 3

Microsoft Office Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats

Microsoft Office Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats Service Pack 1

Microsoft Works 8.0

Microsoft Works 8.5

Microsoft Works 9.0

Microsoft Works Suite 2005

Microsoft Works Suite 2006

Microsoft Office 2004 for Mac

Microsoft Office 2008 for Mac
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Frequently Asked Questions (FAQ) Related to This Security Update

I do not have all of the affected software installed, but I do have other Microsoft Office applications installed. Why am I being offered the security update?
The vulnerabilities described in this security update exist within Microsoft Office but could not be exploited using one of the applications listed in the Non-Affected Software table. The Microsoft Office applications listed in the Non-Affected Software table use some of the same files as the applications listed in the Affected Software table to which the security update applies. We recommend installing the update to prevent the security update from being offered again.

I am using an older release of the software discussed in this security bulletin. What should I do?
The affected software listed in this bulletin have been tested to determine which releases are affected. Other releases are past their support life cycle. To determine the support life cycle for your software release, visit Microsoft Support Lifecycle.

It should be a priority for customers who have older releases of the software to migrate to supported releases to prevent potential exposure to vulnerabilities. For more information about the Windows Product Lifecycle, visit Microsoft Support Lifecycle. For more information about the extended security update support period for these software versions or editions, visit Microsoft Product Support Services.

Customers who require custom support for older releases must contact their Microsoft account team representative, their Technical Account Manager, or the appropriate Microsoft partner representative for custom support options. Customers without an Alliance, Premier, or Authorized Contract can contact their local Microsoft sales office. For contact information, visit Microsoft Worldwide Information, select the country, and then click Go to see a list of telephone numbers. When you call, ask to speak with the local Premier Support sales manager. For more information, see the Windows Operating System Product Support Lifecycle FAQ.
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Vulnerability Information

Severity Ratings and Vulnerability Identifiers
Vulnerability Severity Rating and Maximum Security Impact by Affected Software
Affected Software Vulnerability in Content-Disposition Header Vulnerability - CVE-2008-4020 Aggregate Severity Rating

Microsoft Office XP Service Pack 3

Moderate
Information Disclosure

Moderate
Information Disclosure
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Vulnerability in Content-Disposition Header Vulnerability - CVE-2008-4020

A vulnerability exists in the way that Office processes documents using the CDO Protocol (cdo:) and the Content-Disposition: Attachment header. These documents may be incorrectly rendered in the web browser, leading to cross-site scripting.

To view this vulnerability as a standard entry in the Common Vulnerabilities and Exposures list, see CVE-2008-4020.

Mitigating Factors for Vulnerability in Content-Disposition Header Vulnerability - CVE-2008-4020
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In a Web-based attack scenario, an attacker could host a Web site that contains a Web page that is used to exploit this vulnerability. In addition, compromised Web sites and Web sites that accept or host user-provided content or advertisements could contain specially crafted content that could exploit this vulnerability. In all cases, however, an attacker would have no way to force users to visit these Web sites. Instead, an attacker would have to convince users to visit the Web site, typically by getting them to click a link in an e-mail message or Instant Messenger message that takes users to the attacker's Web site.
•

By default, Internet Explorer on Windows Server 2003 and Windows Server 2008 run in a restricted mode that is known as Enhanced Security Configuration. This mode sets the security level for the Internet zone to High. This is a mitigating factor for Web sites that you have not added to the Internet Explorer Trusted sites zone. See the FAQ subsection of this vulnerability section for more information about Internet Explorer Enhanced Security Configuration.
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Workarounds for Vulnerability in Content-Disposition Header Vulnerability - CVE-2008-4020

Workaround refers to a setting or configuration change that does not correct the underlying vulnerability but would help block known attack vectors before you apply the update. Microsoft has tested the following workarounds and states in the discussion whether a workaround reduces functionality:
•

Disable CDO protocol handler
Disabling the affected protocol will help protect the affected system from attempts to exploit this vulnerability. To disable the affected service, unregister these three registry keys:

'HKLM\SOFTWARE\Classes\PROTOCOLS\Handler\cdo'
'HKLM\SOFTWARE\Classes\CDO'
'HKCR\PROTOCOLS\Handler\cdo'

Warning If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use the Registry Editor at your own risk. For information about how to edit the registry, view the "Changing Keys And Values" Help topic in Registry Editor (Regedit.exe) or view the "Add and Delete Information in the Registry" and "Edit Registry Data" Help topics in Regedt32.exe.

Note We recommend backing up the registry before you edit it.
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FAQ for Vulnerability in Content-Disposition Header Vulnerability - CVE-2008-4020

What is the scope of the vulnerability?
This is an information disclosure vulnerability. An attacker who successfully exploited this vulnerability could inject a client side script in the user's browser that could spoof content, disclose information, or take any action that the user could take on the affected Web site.

What causes the vulnerability?
As described in the Microsoft Knowledge Base article 260519, when the header "content-disposition: attachment" is provided, a protocol should raise a File Download dialog box rather than rendering the content. The CDO Protocol (cdo:) does not properly process this header and always renders the content.

What is cross-site scripting?
Cross-site scripting (XSS) is a class of security vulnerability that can enable an attacker to "inject" script code into a user's session with a Web site. The vulnerability can affect Web servers that dynamically generate HTML pages. If these servers embed browser input in the dynamic pages that they send back to the browser, these servers can be manipulated to include maliciously supplied content in the dynamic pages. This can allow malicious script to be executed. Web browsers may perpetuate this problem through their assumptions of "trusted" sites and their use of cookies to maintain persistent state with the Web sites that they frequent. An XSS attack does not modify Web site content. Instead, it inserts new, malicious script that can execute at the browser in the context that is associated with a trusted server.

How does cross-site scripting work?
Web pages contain text and HTML markup. Text and HTML markup are generated by the server and are interpreted by the client. If untrusted content is introduced into a dynamic page, neither the server nor the client has sufficient information to recognize that this injection has occurred and to take protective measures.

What might an attacker use the vulnerability to do?
The attacker could spoof content, disclose information, or take any action that the user could take on the affected Web site.

How could an attacker exploit the vulnerability?
An attacker could exploit this vulnerability by convincing the user to click on a hyperlink to a site that is trusted by the user, that utilizes the content-disposition: attachment flag, and that allows the attacker to post content such as HTML pages.

What systems are primarily at risk from the vulnerability?
Systems running Microsoft Office XP Service Pack 3 are primarily at risk

What does the update do?
The update removes the vulnerability by unregistering the CDO Protocol.

When this security bulletin was issued, had this vulnerability been publicly disclosed?
No. Microsoft received information about this vulnerability through responsible disclosure. Microsoft had not received any information to indicate that this vulnerability had been publicly disclosed when this security bulletin was originally issued. This security bulletin addresses the privately disclosed vulnerability as well as additional issues discovered through internal investigations.

When this security bulletin was issued, had Microsoft received any reports that this vulnerability was being exploited?
No. Microsoft had not received information to indicate that this vulnerability had been publicly used to attack customers and had not seen any examples of proof of concept code published when this security bulletin was originally issued.

Other Information
Acknowledgments

Microsoft thanks the following for working with us to help protect customers:
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NetAgent Co., Ltd. for reporting the Vulnerability in Content Disposition Header Vulnerability (CVE-2008-4020).

Support
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Customers in the U.S. and Canada can receive technical support from Microsoft Product Support Services at 1-866-PCSAFETY. There is no charge for support calls that are associated with security updates.
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International customers can receive support from their local Microsoft subsidiaries. There is no charge for support that is associated with security updates. For more information about how to contact Microsoft for support issues, visit the International Support Web site.

Disclaimer

The information provided in the Microsoft Knowledge Base is provided "as is" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.

Revisions
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V1.0 (October 14, 2008): Bulletin published.