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Microsoft Security Bulletin MS11-061 - Important

Vulnerability in Remote Desktop Web Access Could Allow Elevation of Privilege (2546250)

Published: August 09, 2011

Version: 1.0

General Information

Executive Summary

This security update resolves a privately reported vulnerability in Remote Desktop Web Access. The vulnerability is a cross-site scripting (XSS) vulnerability that could allow elevation of privilege, enabling an attacker to execute arbitrary commands on the site in the context of the target user. The XSS Filter in Internet Explorer 8 and Internet Explorer 9 prevents this attack for its users when browsing to a Remote Desktop Web Access server in the Internet Zone. The XSS Filter in Internet Explorer 8 and Internet Explorer 9 is not enabled by default in the Intranet Zone.

This security update is rated Important for all supported editions of Windows Server 2008 R2. For more information, see the subsection, Affected and Non-Affected Software, in this section.

The security update addresses the vulnerability by correcting the manner in which the logon page for Remote Desktop Web Access validates input parameters. 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. The majority of customers have automatic updating enabled and will not need to take any action because this security update will be downloaded and installed automatically. Customers who have not enabled automatic updating need to check for updates and install this update manually. For information about specific configuration options in automatic updating, see Microsoft Knowledge Base Article 294871.

For administrators and enterprise installations, or end users who want to install this security update manually, Microsoft recommends that customers apply the update at the earliest opportunity using update management software, or by checking for updates using the Microsoft Update service.

See also the section, Detection and Deployment Tools and Guidance, later in this bulletin.

Known Issues. Microsoft Knowledge Base Article 2546250 documents the currently known issues that customers may experience when installing this security update. The article also documents recommended solutions for these issues.

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

Operating SystemMaximum Security ImpactAggregate Severity RatingBulletins Replaced by this Update
Windows Server 2008 R2 for x64-based Systems and Windows Server 2008 R2 for x64-based Systems Service Pack 1**Elevation of PrivilegeImportantNone

**Server Core installation not affected. The vulnerabilities addressed by this update do not affect supported editions of Windows Server 2008 or Windows Server 2008 R2 as indicated, when installed using the Server Core installation option. For more information on this installation option, see the TechNet articles, Managing a Server Core Installation and Servicing a Server Core Installation. Note that the Server Core installation option does not apply to certain editions of Windows Server 2008 and Windows Server 2008 R2; see Compare Server Core Installation Options.

Non-Affected Software

Operating System
Windows XP Service Pack 3
Windows XP Professional x64 Edition Service Pack 2
Windows Server 2003 Service Pack 2
Windows Server 2003 x64 Edition Service Pack 2
Windows Server 2003 with SP2 for Itanium-based Systems
Windows Vista Service Pack 2
Windows Vista x64 Edition Service Pack 2
Windows Server 2008 for 32-bit Systems Service Pack 2
Windows Server 2008 for x64-based Systems Service Pack 2
Windows Server 2008 for Itanium-based Systems Service Pack 2
Windows 7 for 32-bit Systems and Windows 7 for 32-bit Systems Service Pack 1
Windows 7 for x64-based Systems and Windows 7 for x64-based Systems Service Pack 1
Windows Server 2008 R2 for Itanium-based Systems and Windows Server 2008 R2 for Itanium-based Systems Service Pack 1

I have customized my web enrollment ASP pages. Do I need to be concerned with the known issues listed in Microsoft Knowledge Base Article 2546250? 
Yes, Microsoft recommends that customers who have edited their Web enrollment ASP pages should visit Microsoft Knowledge Base Article 2546250 for important information about known issues that may apply to their systems.

Where are the file information details? 
Refer to the reference tables in the Security Update Deployment section for the location of the file information details.

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. For more information about the product lifecycle, visit the Microsoft Support Lifecycle Web site.

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. To determine the support lifecycle for your software release, see Select a Product for Lifecycle Information. For more information about service packs for these software releases, see Lifecycle Supported Service Packs.

Customers who require custom support for older software 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 the Microsoft Worldwide Information Web site, select the country in the Contact Information list, 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 Microsoft Support Lifecycle Policy FAQ.

Vulnerability Information

The following severity ratings assume the potential maximum impact of the vulnerability. For information regarding the likelihood, within 30 days of this security bulletin's release, of the exploitability of the vulnerability in relation to its severity rating and security impact, please see the Exploitability Index in the August bulletin summary. For more information, see Microsoft Exploitability Index.

Vulnerability Severity Rating and Maximum Security Impact by Affected Software
Affected SoftwareRemote Desktop Web Access Vulnerability - CVE-2011-1263Aggregate Severity Rating
Windows Server 2008 R2 for x64-based Systems and Windows Server 2008 R2 for x64-based Systems Service Pack 1**Important 
Elevation of Privilege
Important

**Server Core installation not affected. The vulnerabilities addressed by this update do not affect supported editions of Windows Server 2008 or Windows Server 2008 R2 as indicated, when installed using the Server Core installation option. For more information on this installation option, see the TechNet articles, Managing a Server Core Installation and Servicing a Server Core Installation. Note that the Server Core installation option does not apply to certain editions of Windows Server 2008 and Windows Server 2008 R2; see Compare Server Core Installation Options.

A reflected XSS vulnerability exists in Remote Desktop Web Access that could allow an attacker to inject a client-side script into the user's instance of Internet Explorer. This script could spoof content, disclose information, or take any action that the user could take on the Remote Desktop Web Access site.

To view this vulnerability as a standard entry in the Common Vulnerabilities and Exposures list, see CVE-2011-1263.

Mitigating Factors for Remote Desktop Web Access Vulnerability - CVE-2011-1263

Mitigation refers to a setting, common configuration, or general best-practice, existing in a default state, that could reduce the severity of exploitation of a vulnerability. The following mitigating factors may be helpful in your situation:

  • The XSS Filter in Internet Explorer 8 and Internet Explorer 9 prevents this attack for its users when browsing to a Remote Desktop Web Access server in the Internet Zone. The XSS Filter in Internet Explorer 8 and Internet Explorer 9 is not enabled by default in the Intranet Zone.
  • 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 persuade 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.
  • Remote Desktop Web Access is not installed by default. You must install the Remote Desktop Web Access role service on the server that you want users to connect to over the Web to access RemoteApp programs. When you install Remote Desktop Web Access, Microsoft Internet Information Services (IIS) is also installed as a required component.

Workarounds for Remote Desktop Web Access Vulnerability - CVE-2011-1263

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:

  • Enable Internet Explorer 8 and Internet Explorer 9 XSS filter for Intranet Zone
    1. On the Internet Explorer Tools menu, click Internet Options.
    2. In the Internet Options dialog box, click the Security tab, and then click the Local Intranet icon.
    3. Under Security level for this zone, click Custom Level…
    4. Scroll down to Enable XSS Filter (near end of list).
    5. Change the default Disable to Enable.
    6. Click OK, then click Yes on the Are you sure you want to change the settings for this zone? dialog.
    7. Click OK on the Internet Options dialog.

    Impact of workaround. Internal sites not previously flagged as being XSS risks would be flagged.

    How to undo the workaround.

    1. On the Internet Explorer Tools menu, click Internet Options.
    2. In the Internet Options dialog box, click the Security tab, and then click the Local Intranet icon.
    3. Under Security level for this zone, click Custom Level…
    4. Scroll down to Enable XSS Filter (near end of list).
    5. Change the default Enable to Disable.
    6. Click OK, then click Yes on the Are you sure you want to change the settings for this zone? dialog.
    7. Click OK on the Internet Options dialog.

FAQ for Remote Desktop Web Access Vulnerability - CVE-2011-1263

What is the scope of the vulnerability? 
This is a reflected XSS vulnerability that could allow an elevation of privilege.

What causes the vulnerability? 
The vulnerability is caused when the logon page for Remote Desktop Web Access improperly validates a URL parameter.

What is Remote Desktop Web Access? 
Remote Desktop Web Access (RD Web Access) is a role service in the Remote Desktop Services role that lets you make RemoteApp programs, virtual desktops, and session-based desktops available to users by using a Web browser. Additionally, RD Web Access enables users to connect from a Web browser to the remote desktop of any server or client computer where they have the appropriate access. For more information, see the TechNet article, Remote Desktop Web Access.

What is cross-site scripting (XSS)? 
Cross-site scripting (XSS) is a class of security vulnerability that can enable an attacker to inject script into the response to a Web page request. This script is then run by the requesting application, oftentimes a Web browser. The script could then spoof content, disclose information, or take any action that the user could take on the affected Web site, on behalf of the targeted user.

What might an attacker use the vulnerability to do? 
An attacker who successfully exploited this vulnerability could inject a client-side script into the user's instance of Internet Explorer. The script could spoof content, disclose information, or take any action that the user could take on the Remote Desktop Web Access site.

How could an attacker exploit the vulnerability? 
In an e-mail attack scenario, an attacker could exploit the vulnerability by sending a specially crafted link to the user and convincing the user to click the link.

What systems are primarily at risk from the vulnerability? 
Servers running the Remote Desktop Web Access role are primarily at risk. Servers not running this specific role are not at risk.

What does the update do? 
The update addresses the vulnerability by correcting the manner in which the logon page for Remote Desktop Web Access validates input parameters.

When this security bulletin was issued, had this vulnerability been publicly disclosed? 
No. Microsoft received information about this vulnerability through coordinated vulnerability disclosure.

When this security bulletin was issued, had Microsoft received any reports that this vulnerability was being exploited? 
No. Microsoft had not received any information to indicate that this vulnerability had been publicly used to attack customers when this security bulletin was originally issued.

Update Information

Security Central

Manage the software and security updates you need to deploy to the servers, desktop, and mobile systems in your organization. For more information see the TechNet Update Management Center. The Microsoft TechNet Security Web site provides additional information about security in Microsoft products.

Security updates are available from Microsoft Update and Windows Update. Security updates are also available from the Microsoft Download Center. You can find them most easily by doing a keyword search for "security update."

Finally, security updates can be downloaded from the Microsoft Update Catalog. The Microsoft Update Catalog provides a searchable catalog of content made available through Windows Update and Microsoft Update, including security updates, drivers and service packs. By searching using the security bulletin number (such as, "MS07-036"), you can add all of the applicable updates to your basket (including different languages for an update), and download to the folder of your choosing. For more information about the Microsoft Update Catalog, see the Microsoft Update Catalog FAQ.

Detection and Deployment Guidance

Microsoft provides detection and deployment guidance for security updates. This guidance contains recommendations and information that can help IT professionals understand how to use various tools for detection and deployment of security updates. For more information, see Microsoft Knowledge Base Article 961747.

Microsoft Baseline Security Analyzer

Microsoft Baseline Security Analyzer (MBSA) allows administrators to scan local and remote systems for missing security updates as well as common security misconfigurations. For more information about MBSA, visit Microsoft Baseline Security Analyzer.

The following table provides the MBSA detection summary for this security update.

Software MBSA
Windows Server 2008 R2 for x64-based Systems and Windows Server 2008 R2 for x64-based Systems Service Pack 1Yes

Note For customers using legacy software not supported by the latest release of MBSA, Microsoft Update, and Windows Server Update Services, please visit Microsoft Baseline Security Analyzer and reference the Legacy Product Support section on how to create comprehensive security update detection with legacy tools.

Windows Server Update Services

Windows Server Update Services (WSUS) enables information technology administrators to deploy the latest Microsoft product updates to computers that are running the Windows operating system. For more information about how to deploy security updates using Windows Server Update Services, see the TechNet article, Windows Server Update Services.

Systems Management Server

The following table provides the SMS detection and deployment summary for this security update.

SoftwareSMS 2003 with ITMUConfiguration Manager 2007
Windows Server 2008 R2 for x64-based Systems and Windows Server 2008 R2 for x64-based Systems Service Pack 1YesYes

Note Microsoft discontinued support for SMS 2.0 on April 12, 2011. For SMS 2003, Microsoft also discontinued support for the Security Update Inventory Tool (SUIT) on April 12, 2011. Customers are encouraged to upgrade to System Center Configuration Manager 2007. For customers remaining on SMS 2003 Service Pack 3, the Inventory Tool for Microsoft Updates (ITMU) is also an option.

For SMS 2003, the SMS 2003 Inventory Tool for Microsoft Updates (ITMU) can be used by SMS to detect security updates that are offered by Microsoft Update and that are supported by Windows Server Update Services. For more information about the SMS 2003 ITMU, see SMS 2003 Inventory Tool for Microsoft Updates. For more information about SMS scanning tools, see SMS 2003 Software Update Scanning Tools. See also Downloads for Systems Management Server 2003.

System Center Configuration Manager 2007 uses WSUS 3.0 for detection of updates. For more information about Configuration Manager 2007 Software Update Management, visit System Center Configuration Manager 2007.

For more information about SMS, visit the SMS Web site.

For more detailed information, see Microsoft Knowledge Base Article 910723: Summary list of monthly detection and deployment guidance articles.

Update Compatibility Evaluator and Application Compatibility Toolkit

Updates often write to the same files and registry settings required for your applications to run. This can trigger incompatibilities and increase the time it takes to deploy security updates. You can streamline testing and validating Windows updates against installed applications with the Update Compatibility Evaluator components included with Application Compatibility Toolkit.

The Application Compatibility Toolkit (ACT) contains the necessary tools and documentation to evaluate and mitigate application compatibility issues before deploying Microsoft Windows Vista, a Windows Update, a Microsoft Security Update, or a new version of Windows Internet Explorer in your environment.

Affected Software

For information about the specific security update for your affected software, click the appropriate link:

Windows Server 2008 R2 (all editions)

Reference Table

The following table contains the security update information for this software. You can find additional information in the subsection, Deployment Information, in this section.

Inclusion in Future Service PacksThe update for this issue will be included in a future service pack or update rollup
Deployment
Installing without user interventionFor all supported x64-based editions of Windows Server 2008 R2:
Windows6.1-KB2546250-x64.msu /quiet
Installing without restartingFor all supported x64-based editions of Windows Server 2008 R2:
Windows6.1-KB2546250-x64.msu /quiet /norestart
Further informationSee the subsection, Detection and Deployment Tools and Guidance
Restart Requirement
Restart required?This update does not require a restart. The installer stops the required services, applies the update, and then restarts the services. However, if the required services cannot be stopped for any reason, or if required files are being used, this update will require a restart. If this behavior occurs, a message appears that advises you to restart.
HotPatchingNot applicable.
Removal InformationThis security update cannot be deleted.
File InformationSee Microsoft Knowledge Base Article 2546250
Registry Key VerificationNote A registry key does not exist to validate the presence of this update.

Deployment Information

Installing the Update

When you install this security update, the installer checks whether one or more of the files that are being updated on your system have previously been updated by a Microsoft hotfix.

For more information about the terminology that appears in this bulletin, such as hotfix, see Microsoft Knowledge Base Article 824684.

This security update supports the following setup switches.

Supported Security Update Installation Switches
SwitchDescription
/?, /h, /helpDisplays help on supported switches.
/quietSuppresses the display of status or error messages.
/norestartWhen combined with /quiet, the system will not be restarted after installation even if a restart is required to complete installation.
/warnrestart:<seconds>When combined with /quiet, the installer will warn the user before initiating restart.
/promptrestartWhen combined with /quiet, the installer will prompt before initiating restart.
/forcerestartWhen combined with /quiet, the installer will forcefully close applications and initiate restart.
/log:<file name>Enables logging to specified file.
/extract:<destination>Extracts the package contents to the destination folder.
/uninstall /kb:<KB Number>Uninstalls the security update.

Note For more information about the wusa.exe installer, see "Windows Update Stand-alone Installer" in the TechNet article, Miscellaneous Changes in Windows 7.

Verifying That the Update Has Been Applied

  • Microsoft Baseline Security Analyzer

    To verify that a security update has been applied to an affected system, you may be able to use the Microsoft Baseline Security Analyzer (MBSA) tool. See the section, Detection and Deployment Tools and Guidance, earlier in this bulletin for more information.

  • File Version Verification

    Because there are several editions of Microsoft Windows, the following steps may be different on your system. If they are, see your product documentation to complete these steps.

    1. Click Start and then enter an update file name in the Start Search box.
    2. When the file appears under Programs, right-click the file name and click Properties.
    3. On the General tab, compare the file size with the file information tables provided in the bulletin KB article.

      Note Depending on the edition of the operating system, or the programs that are installed on your system, some of the files that are listed in the file information table may not be installed.
    4. You can also click the Details tab and compare information, such as file version and date modified, with the file information tables provided in the bulletin KB article.

      Note Attributes other than the file version may change during installation. Comparing other file attributes to the information in the file information table is not a supported method of verifying that the update has been applied. Also, in certain cases, files may be renamed during installation. If the file or version information is not present, use one of the other available methods to verify update installation.
    5. Finally, you can also click the Previous Versions tab and compare file information for the previous version of the file with the file information for the new, or updated, version of the file.

Other Information

Acknowledgments

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

  • Sven Taute for reporting the Remote Desktop Web Access Vulnerability (CVE-2011-1263)

Microsoft Active Protections Program (MAPP)

To improve security protections for customers, Microsoft provides vulnerability information to major security software providers in advance of each monthly security update release. Security software providers can then use this vulnerability information to provide updated protections to customers via their security software or devices, such as antivirus, network-based intrusion detection systems, or host-based intrusion prevention systems. To determine whether active protections are available from security software providers, please visit the active protections Web sites provided by program partners, listed in Microsoft Active Protections Program (MAPP) Partners.

Support

  • Customers in the U.S. and Canada can receive technical support from Security Support or 1-866-PCSAFETY. There is no charge for support calls that are associated with security updates. For more information about available support options, see Microsoft Help and Support.
  • 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

  • V1.0 (August 9, 2011): Bulletin published.

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