Security Bulletin

Microsoft Security Bulletin MS03-047 - Moderate

Vulnerability in Exchange Server 5.5 Outlook Web Access Could Allow Cross-Site Scripting Attack (828489)

Published: October 15, 2003 | Updated: April 12, 2004

Version: 2.1

Issued: October 15, 2003
Updated: April 12, 2004
Version Number: 2.1

See all Exchange Server bulletins released October, 2003

Summary

Who Should Read This Document:   System administrators who have servers running Microsoft® Exchange Server 5.5 Outlook® Web Access

Impact of Vulnerability:   Remote Code Execution

Maximum Severity Rating:   Moderate

Recommendation:   System administrators should install this security patch on their servers running Outlook Web Access 5.5

Patch Replacement: This patch replaces Microsoft Security Bulletin MS01-057.

Caveats:   Customers who have customized any of the ASP pages in the File Information section in this document should backup those files before applying this patch as they will be overwritten when the patch is applied. Any customizations would then need to be reapplied to the new ASP pages.

• Version Requirements for Dependent Components for this patch:

  To install successfully, this patch requires that the OWA server have Internet Explorer 5.01 or greater installed.

• Version Recommendations for Dependent Components for OWA:

  At the time of this writing, the following versions are recommended for dependent components on the OWA server:

  • IIS:
    • IIS Version 4.0 on Windows NT 4.0 SP6
    • IIS Version 5.0 on Windows 2000 SP2 or greater
  • IE:
    • IE Version 5.5 SP2
    • IE Version 6.0

Tested Software and Patch Download Locations:

Affected Software:

• Microsoft Exchange Server 5.5, Service Pack 4 - Download the patch

Non Affected Software:

• Microsoft Exchange 2000 Server
• Microsoft Exchange Server 2003

The software listed above has been tested to determine if the above versions are affected. Other versions are no longer supported, and may or may not be affected.

General Information

Technical Details

Technical Description:

Subsequent to the original release of this bulletin, it was discovered that certain languages were not covered by the original patch. This bulletin has been updated to provide information about a new patch, which is intended for customers having installed a language from the Language Packs for Outlook Web Access.

In addition, for this patch to function properly the Outlook Web Access (OWA) server on which the patch is installed must have Internet Explorer 5.01 or greater installed. If the patch is installed on a system with a version of IE less than 5.01, unexpected consequences may result. The "Caveats" section has been updated to include version requirements for this patch. It also contains version recommendations for dependent components that are applicable at the time of this writing. The deployment section has also been expanded to discuss in detail how to download and install this security patch.

A cross-site scripting (XSS) vulnerability results due to the way that Outlook Web Access (OWA) performs HTML encoding in the Compose New Message form.

An attacker could seek to exploit this vulnerability by having a user run script on the attacker's behalf. The script would execute in the security context of the user. If the script executes in the security context of the user, the attacker's code could then execute by using the security settings of the OWA Web site (or of a Web site that is hosted on the same server as the OWA Web site) and could enable the attacker to access any data belonging to the site where the user has access.

To exploit this vulnerability through OWA, an attacker would have to send an e-mail message that has a specially-formed link to the user. The user would then have to click the link. To exploit this vulnerability in another way, an attacker would have to know the name of the user's Exchange server and then entice the user to open a specially-formed link from another source while the user is logged on to OWA.

Note: Customers who have customized any of the ASP pages in the File Information section in this document should backup those files before applying this patch as they will be overwritten when the patch is applied. Any customizations would then need to be reapplied to the new ASP pages. Please refer to the Microsoft Support Policy for the Customization of Outlook Web Access available at https:

Mitigating factors:

• To be affected, the user would have to be logged onto OWA, be enticed to log on to OWA, or use another Web application on the same server as OWA. Generally, a server that runs Exchange Server 5.5 Outlook Web Access does not run other Web applications for reasons of performance, scalability, and security.
• To exploit this vulnerability through OWA, an attacker would have to send an e-mail message that has a specially-formed link to a user. The user would then have to click the link.
• In the Web-based attack vector, an attacker would have to know the name of a user's Exchange server and then entice the user to open a specially-formed link from some other source while the user is logged on to OWA.

Severity Rating:

The above assessment is based on the types of systems affected by the vulnerability, their typical deployment patterns, and the effect that exploiting the vulnerability would have on them.

Vulnerability identifier: CAN-2003-0712

Workarounds

Microsoft has tested the following workarounds. These workarounds will not correct the underlying vulnerability however they help block known attack vectors. Workarounds may cause a reduction in functionality in some cases - in such situations this is identified below.

• Disable Outlook Web Access for each Exchange site

  Outlook Web Access can be disabled by following these steps. These steps need to be performed on each Exchange site.

  1. Start Exchange Administrator
  2. Expand the Configuration container for the site.
  3. Select the Protocols container for the site.
  4. Open the properties of the HTTP (Web) Site Settings object
  5. Clear the "Enable Protocol" checkbox.
  6. Wait for the change to replicate, and then verify that this change has replicated to each server in the site. To do this, bind to each server in the site with Exchange Administrator and view the setting.

  Impact of Workaround: Users will have no access to their mailboxes via Outlook Web Access.

• Uninstall Outlook Web Access.

  Uninstall Outlook Web Access. For steps on how to do this please refer to the Knowledge Base Article "How to Completely Remove and Re-Install OWA" available at </https:>https:

  Impact of Workaround: Users will have no access to their mailboxes via Outlook Web Access.

For additional information about how to help make your Exchange environment more secure, visit the Security Resources for Exchange 5.5 Web site.

Frequently Asked Questions

Microsoft has issued a new patch for additional Outlook Web Access languages. Why?
Subsequent to the original release of this bulletin, it was discovered that certain languages were not covered by the original patch. This bulletin has been updated to provide information about a new patch, which is intended for customers having installed a language from the Language Packs for Outlook Web Access.

I have already installed the original patch. Do I need to install the new patch?
The original patch is still effective in removing the security vulnerability if your Outlook Web Access pages are displayed in German, English, French, or Japanese. The new patch adds support for additional languages available through the Outlook Web Access language pack and does not alter the original patch for the above mentioned languages. If you have added a language from the Language Packs for Outlook Web Access then you do need to apply this new patch.

What is the scope of this vulnerability?
This is a cross-site scripting vulnerability. This vulnerability could enable an attacker to cause arbitrary code to run during another user's Web session. The code could take any action on the user's computer that the Web site is authorized to take; this could include monitoring the Web session and forwarding information to a third party, running other code on the user's system and reading or writing cookies. The code could be written to be persistent, so that if the user returned to the Web site again, the code would run again. The vulnerability cannot be "injected" into a Web session; it can only be exploited if the user clicks a hyperlink that the attacker provides. To exploit this vulnerability in another way, other then sending the specially formed link in email to a user, an attacker would have to know the name of a user's Exchange server and then entice the user to open a specially-formed link from some other source while the user is logged on to OWA.

What is Outlook Web Access?
Microsoft Outlook Web Access (OWA) is a service of Exchange Server. By using OWA, users can use a Web browser to access their Exchange mailbox. By using OWA, a server that is running Exchange Server can also function as a Web site that lets authorized users read or send mail, manage their calendar, or perform other mail functions over the Internet.

What is cross-site scripting?
Cross-site scripting (XSS) is a security vulnerability that could enable an attacker to "inject" code into a user's session with a Web site. Unlike most security vulnerabilities, XSS does not apply to any single vendor's products - instead, it can affect any software that generates HTML and that does not follow defensive programming practices.

How does XSS work?
Web pages contain text and HTML markup, which are generated by the server and are interpreted by the client. Servers that generate static pages have full control over the way that the client interprets the pages that the server sends. However, servers that generate dynamic pages do not have control over the way that the client interprets their output. If untrusted content can be introduced into a dynamic page, neither the server nor the client has sufficient information to recognize that this has occurred and to take protective actions. More information about how cross-site scripting works and what can be done to mitigate such attacks can be found at Information about Cross-Site Scripting Security Vulnerability.

What causes the vulnerability?
The vulnerability results because the Active Server Page (ASP) that Exchange Server 5.5 Outlook Web Access uses when it composes new messages replays the requested URL in HTML without the correct encoding.

What is wrong with Outlook Web Access?
When a user creates a new e-mail message, OWA does not correctly encode the URL for display in HTML. As a result, an attacker could embed a link to a script on a separate Web site and could cause the link to be returned to the Web browser in such a way that the browser thinks that it comes from the OWA Web site.

What could this vulnerability enable an attacker to do?
The vulnerability could enable an attacker who hosts a malicious Web site, or who can entice a user to click a specially-formed link, to carry out a cross-site scripting attack against the user's OWA Web site. By doing so, an attacker could run script in the user's browser and could use the security settings of the OWA Web site or any other Web site that is hosted on the same system and to could access cookies and other data that belong to the Web site.

How could an attacker exploit this vulnerability?
An attacker who hosts a malicious Web site could seek to exploit this vulnerability by sending a specially-crafted e-mail message that has an embedded script or link that, when accessed, would send out a Web server query that has a script as part of one of the arguments. The user would have to click the link in the e-mail message while it appears in OWA or while it appears on an external Web site.

Are all versions of OWA are vulnerable?
No. The vulnerability affects only Exchange Server 5.5 Outlook Web Access.

On which Exchange servers should I install the patch?
This patch is intended only for servers that are running Exchange Server 5.5 Outlook Web Access. You do not have to install this patch on servers that are not running Exchange Server 5.5 Outlook Web Access.

I have customized my OWA site, what do I do?
Customers having customized any of the ASP pages in the File Information section in this document should backup those files before applying this patch as they will be overwritten when the patch is applied. Any customizations would then need to be reapplied to the new ASP pages. Please refer to the Microsoft Support Policy for the Customization of Outlook Web Access available at </https:>https:

How does the patch eliminate the vulnerability?
The patch eliminates the vulnerability by ensuring that OWA script arguments are encoded so that they cannot be unintentionally executed.

Security Patch Information

For information about the specific security patch for your platform, click the appropriate link:

Exchange Server 5.5 Service Pack 4

Prerequisites:

This security patch requires Outlook Web Access on Exchange Server 5.5 Service Pack 4.

Installation Information:

For additional information about the command options that you can use to apply this update, click the article number below to view the article in the Microsoft Knowledge Base:

257946 XGEN: GUI Hotfix Utility Switches /x /m /s /z

Deployment Information

Two packages for each server language have been combined into one self-extracting cabinet with the following name:

• Exchange5.5-KB828489-v2-x86-<serverlang>.EXE

where <serverlang> is the language of your installed Exchange Server:

• DEU = German
• ENU = English
• FRA = French
• JPN = Japanese

When you run the package it will extract the two packages to a folder that youhave chosen with the following names:

• Exchange5.5-KB828489-v2a-x86-<serverlang>.EXE
• Exchange5.5-KB828489-v2b-x86-INTL.EXE

How to install:

If you installed the original security patch for MS03-047 (Exchange5.5-KB828489-x86-<serverlang>, then you must uninstall it before installing the updated security patch. Refer to the section "Removal Information" below for instructions on how to do this.

1. You must install the "v2a" patch (Exchange5.5-KB828489-v2a-x86-<serverlang>.EXE) on all servers where you want to apply this security patch. This package will update the following three things:
   • Updates the Exchange Server's CDO.DLL
   • Updates the OWA language that matches the language of the installed Exchange Server
   • Update any of the following OWA languages if they are installed:
     • Chinese (Simplified)
     • Chinese (Traditional)
     • English
     • French
     • German
     • Italian
     • Japanese
     • Korean
     • Polish
     • Russian
     • Spanish
2. Once the installation of "v2a" patch is complete you will only need to install "v2b" patch (Exchange5.5-KB828489-v2b-x86-INTL.EXE) if your server has one or more of the following OWA languages installed:
   • Brazilian
   • Czech
   • Danish
   • Dutch
   • Finnish
   • Greek
   • Hungarian
   • Norwegian
   • Portuguese
   • Swedish
   • Turkish

Note:

• Do not uninstall the "v2a" patch even if you only use languages within "v2b" as this could break some functionality.
• Only the language packs that are installed will be updated. This package does not install languages that are not already installed.
• If you installed the original security patch, the "v2a" patch will require you to first uninstall that patch. This is being done so that if you later have to uninstall the "v2a" patch it will put the server back to a known and supported state. If you need to uninstall both "v2a" and "v2b", then remove them in the reverse order that they were installed.
• Patch "v2b" checks if "v2a" is already installed. If "v2a" is not installed it will block install and pop up a message saying that you must install the "v2a" patch first.
• You may get a blank message body when opening a message in OWA after the patch is installed if you have your Windows directory on the OWA Server set to read only permissions. To solve this problem, please reference the following Knowledge Base Article: https://support.microsoft.com/default.aspx?scid=KB;EN-US;314532

Restart Requirement:

No. However, the security patch will restart Microsoft Internet Information Services (IIS), the Exchange Store, and the Exchange System Attendant Services. For this reason, install the patch when no users are logged on through OWA.

Removal Information:

To remove this update, use the Add or Remove Programs tool in Control Panel or issue the following command in a console window:

%EXCHSRVR%\828489\UNINSTALL\UNINST.EXE

In Add / Remove Programs the original package is named Microsoft Update 828489 for Exchange 5.5.

The updated packages are named Hotfix for Exchange 5.5 v2a (KB828489a) and Hotfix for Exchange 5.5 v2b (KB828489b) respectively.

File Information:

The English version of this fix has the file attributes (or later) that are listed in the following table. The dates and times for these files are listed in coordinated universal time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time tool in Control Panel.

Verifying patch installation:

To verify that the security patch is installed on your computer use the Microsoft Baseline Security Analyzer (MBSA) tool. For additional information about MBSA, click the following article number to view the article in the Microsoft Knowledge Base:

320454Microsoft Baseline Security Analyzer Version 1.1.1 Is Available

You may also be able to verify the files that this security patch installed by reviewing the following registry keys:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Updates\Exchange Server 5.5\SP5\828489a

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Updates\Exchange Server 5.5\SP5\828489b

Note: These registry keys may not be not created properly when an administrator or an OEM integrates or slipstreams the 828489 security patch into the Windows installation source files.

Other Information

Acknowledgments

Microsoft thanks the following for working with us to protect customers:

• Ory Segal of Sanctum Inc. for reporting the issue described in MS03-047.

Obtaining other security patches:

Patches for other security issues are available from the following locations:

• Security patches are available from the Microsoft Download Center, and can be most easily found by doing a keyword search for "security_patch".
• Patches for consumer platforms are available from the WindowsUpdate web site

Support:

• Technical support is available from Microsoft Product Support Services at 1-866-PCSAFETY. There is no charge for support calls associated with security patches.

Security Resources:

• The Microsoft TechNet Security Web Site provides additional information about security in Microsoft products.
• Microsoft Software Update Services: </https:>https:
• Microsoft Baseline Security Analyzer (MBSA) details: https://www.microsoft.com/mbsa. Please see https://support.microsoft.com/default.aspx?scid=kb;EN-US;306460 for list of security patches that have detection limitations with MBSA tool.
• Windows Update Catalog: https://support.microsoft.com/default.aspx?scid=kb;EN-US;323166
• Windows Update: https://windowsupdate.microsoft.com
• Office Update: </https:>https:

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:

• V1.0 October 15, 2003: First Published.
• V1.1 October 21, 2003:
  • Removed unnecessary information from "Deployment" in the "Exchange Server 5.5 Service Pack 4" section of "Security Patch Information."
  • Updated product specific information in the "Exchange Server 5.5 Service Pack 4" section of "Security Patch Information."
  • Updated link in the "Severity Rating" section of "Technical Details".
• V2.0 October 22, 2003: Updated to include details of an additional patch for languages available through the Outlook Web Access language pack.
• V2.1 April 12, 2004: Updated correct registry entries.

Built at 2014-04-18T13:49:36Z-07:00 </https:>