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Microsoft Security Bulletin MS11-005 - Important

Vulnerability in Active Directory Could Allow Denial of Service (2478953)

Published: February 08, 2011

Version: 1.0

General Information

Executive Summary

This security update resolves a publicly disclosed vulnerability in Active Directory. The vulnerability could allow denial of service if an attacker sent a specially crafted packet to an affected Active Directory server. The attacker must have valid local administrator privileges on the domain-joined computer in order to exploit this vulnerability.

This security update is rated Important for Active Directory on all supported editions of Windows Server 2003. For more information, see the subsection, Affected and Non-Affected Software, in this section.

The security update addresses the vulnerability by correcting the way that the Active Directory server handles service principal name (SPN) update requests. 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. None

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 SystemComponentMaximum Security ImpactAggregate Severity RatingBulletins Replaced by this Update
Windows Server 2003 Service Pack 2 Active Directory Denial of ServiceImportant MS10-068,
MS10-101
Windows Server 2003 x64 Edition Service Pack 2 Active Directory Denial of ServiceImportant MS10-068,
MS10-101
Windows Server 2003 with SP2 for Itanium-based Systems Active Directory Denial of ServiceImportant MS10-068,
MS10-101

Non-Affected Software

Operating SystemComponent
Windows XP Service Pack 3Active Directory Application Mode (ADAM)
Windows XP Professional x64 Edition Service Pack 2Active Directory Application Mode (ADAM)
Windows Server 2003 Service Pack 2Active Directory Application Mode (ADAM)
Windows Server 2003 x64 Edition Service Pack 2Active Directory Application Mode (ADAM)
Windows Vista Service Pack 1 and Windows Vista Service Pack 2Active Directory Lightweight Directory Service (AD LDS)
Windows Vista x64 Edition Service Pack 1 and Windows Vista x64 Edition Service Pack 2Active Directory Lightweight Directory Service (AD LDS)
Windows Server 2008 for 32-bit Systems and Windows Server 2008 for 32-bit Systems Service Pack 2Active Directory,
Active Directory Lightweight Directory Service (AD LDS)
Windows Server 2008 for x64-based Systems and Windows Server 2008 for x64-based Systems Service Pack 2Active Directory,
Active Directory Lightweight Directory Service (AD LDS)
Windows Server 2008 for Itanium-based Systems and Windows Server 2008 for Itanium-based Systems Service Pack 2(ADAM, AD LDS, and Active Directory are not components of this release of Microsoft Windows)
Windows 7 for 32-bit SystemsActive Directory Lightweight Directory Service (AD LDS)
Windows 7 for x64-based SystemsActive Directory Lightweight Directory Service (AD LDS)
Windows Server 2008 R2 for x64-based SystemsActive Directory,
Active Directory Lightweight Directory Service (AD LDS)
Windows Server 2008 R2 for Itanium-based Systems(ADAM, AD LDS, and Active Directory are not components of this release of Microsoft Windows)

I am running one of the platforms that are listed in the Affected Software table. Why am I not being offered the update? 
The update will only be offered to systems on which the affected component is both installed and enabled. Microsoft Windows Server systems not configured in the role of a domain controller are not affected and will not receive this update.

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 February bulletin summary. For more information, see Microsoft Exploitability Index.

Vulnerability Severity Rating and Maximum Security Impact by Affected Software
Affected SoftwareActive Directory SPN Validation Vulnerability - CVE-2011-0040Aggregate Severity Rating
Active Directory on Windows Server 2003 Service Pack 2 Important 
Denial of Service
Important
Active Directory on Windows Server 2003 x64 Edition Service Pack 2 Important 
Denial of Service
Important
Active Directory on Windows Server 2003 with SP2 for Itanium-based Systems Important 
Denial of Service
Important

A denial of service vulnerability exists in implementations of Microsoft Windows Active Directory due to improper validation of service principal names (SPN), which could result in SPN collisions. When this occurs, services that use the SPN will downgrade to NT LAN Manager (NTLM) if configured to negotiate. Services that are not configured to negotiate will become unavailable, resulting in a denial of service condition. An attacker who successfully exploited this vulnerability could cause the affected system to stop responding.

To view this vulnerability as a standard entry in the Common Vulnerabilities and Exposures list, see CVE-2011-0040.

Mitigating Factors for Active Directory SPN Validation Vulnerability - CVE-2011-0040

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:

  • To exploit this denial of service vulnerability, the attacker must be an administrator on a domain-joined computer.

Workarounds for Active Directory SPN Validation Vulnerability - CVE-2011-0040

Microsoft has not identified any workarounds for this vulnerability.

FAQ for Active Directory SPN Validation Vulnerability - CVE-2011-0040

What is the scope of the vulnerability? 
This is an authentication downgrade as well as a denial of service vulnerability. An attacker who exploited this vulnerability could cause the affected system to downgrade from Kerberos to NT LAN Manager (NTLM), and in the worst case, cause the service to stop responding. Note that this vulnerability would not allow an attacker to execute code or to elevate their user rights.

What causes the vulnerability? 
Active Directory improperly processes specially crafted requests to update the service principal name (SPN) and can result in name collisions in the domain.

What is Active Directory? 
The main purpose of Active Directory is to provide central authentication and authorization services for Windows-based computers.

What is SPN? 
A service principal name (SPN) is the name by which a client uniquely identifies an instance of a service. For more information regarding the use of service principal names, please see MSDN article, Service Principal Names.

What is NTLM? 
Windows Challenge/Response (NT LAN Manager or NTLM) is the authentication protocol used on networks that include systems running the Windows operating system and on stand-alone systems. NTLM credentials are based on data obtained during the interactive logon process and consist of a domain name, a user name, and a one-way hash of the user's password. NTLM uses an encrypted challenge/response protocol to authenticate a user without sending the user's password over the network. Instead, the system requesting authentication must perform a calculation that proves it has access to the secured NTLM credentials.

Interactive NTLM authentication over a network typically involves two systems: a client system, where the user is requesting authentication, and a domain controller, where information related to the user's password is kept. Non-interactive authentication, which may be required to permit an already logged-on user to access a resource such as a server application, typically involves three systems: a client, a server, and a domain controller that does the authentication calculations on behalf of the server.

What is Kerberos? 
Kerberos is a protocol used to mutually authenticate users and services on an open and unsecured network. It allows services to correctly identify the user of a Kerberos ticket without having to authenticate the user at the service. It does this by using shared secret keys.

The Kerberos protocol uses shared secret keys to encrypt and sign users' credentials. A client is authenticated by a Kerberos Key Distribution Center (KDC). After that authentication, the user can request a service ticket to access a specific service on the network. This ticket includes the encrypted authenticated identity of the user.

What might an attacker use the vulnerability to do? 
An attacker who successfully exploited this vulnerability could cause name collisions in the domain, causing the authentication of the services that use the SPN to be downgraded to NTLM. In specific configurations where the service is not configured to negotiate, the service will become unavailable.

How could an attacker exploit the vulnerability? 
An attacker could try to exploit this vulnerability by sending specially crafted packets to the Active Directory server. The attacker must have valid local administrator privileges on the domain-joined computer in order to exploit this vulnerability.

What systems are primarily at risk from the vulnerability? 
This vulnerability affects environments running Active Directory on Windows Server 2003.

What does the update do? 
The update addresses the vulnerability by correcting the way that the Active Directory server handles service principal name (SPN) update requests.

When this security bulletin was issued, had this vulnerability been publicly disclosed? 
Yes. This vulnerability has been publicly disclosed. It has been assigned Common Vulnerability and Exposure number CVE-2011-0040.

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 2003 Service Pack 2Yes
Windows Server 2003 x64 Edition Service Pack 2Yes
Windows Server 2003 with SP2 for Itanium-based SystemsYes

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 2.0SMS 2003 with SUITSMS 2003 with ITMUConfiguration Manager 2007
Windows Server 2003 Service Pack 2YesYesYesYes
Windows Server 2003 x64 Edition Service Pack 2NoNoYesYes
Windows Server 2003 with SP2 for Itanium-based SystemsNoNoYesYes

For SMS 2.0 and SMS 2003, the Security Update Inventory Tool (SUIT) can be used by SMS to detect security updates. See also Downloads for Systems Management Server 2.0.

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 2003 (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 Packs The update for this issue will be included in a future service pack or update rollup
Deployment
Installing without user interventionFor Active Directory on all supported 32-bit editions of Windows Server 2003:
WindowsServer2003-KB2478953-x86-enu.exe /quiet
For Active Directory on all supported x64-based editions of Windows Server 2003:
WindowsServer2003.WindowsXP-KB2478953-x64-enu.exe /quiet
For Active Directory on all supported Itanium-based editions of Windows Server 2003:
WindowsServer2003-KB2478953-ia64-enu.exe /quiet
Installing without restartingFor Active Directory on all supported 32-bit editions of Windows Server 2003:
WindowsServer2003-KB2478953-x86-enu.exe /norestart
For Active Directory on all supported x64-based editions of Windows Server 2003:
WindowsServer2003.WindowsXP-KB2478953-x64-enu.exe /norestart
For Active Directory on all supported Itanium-based editions of Windows Server 2003:
WindowsServer2003-KB2478953-ia64-enu.exe /norestart
Update log fileKB2478953.log
Further informationSee the subsection, Detection and Deployment Tools and Guidance
Restart Requirement
Restart required?Yes, you must restart your system after you apply this security update.
HotPatchingThis security update does not support HotPatching. For more information about HotPatching, see Microsoft Knowledge Base Article 897341.
Removal Information Use Add or Remove Programs tool in Control Panel or the Spuninst.exe utility located in the %Windir%\$NTUninstallKB2478953$\Spuninst folder
File Information See Microsoft Knowledge Base Article 2478953
Registry Key Verification HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Updates\Windows Server 2003\SP3\KB2478953\Filelist

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.

If you have previously installed a hotfix to update one of these files, the installer copies the RTMQFE, SP1QFE, or SP2QFE files to your system. Otherwise, the installer copies the RTMGDR, SP1GDR, or SP2GDR files to your system. Security updates may not contain all variations of these files. For more information about this behavior, see Microsoft Knowledge Base Article 824994.

For more information about the installer, see Microsoft Knowledge Base Article 832475.

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
/help Displays the command-line options.
Setup Modes
/passive Unattended Setup mode. No user interaction is required, but installation status is displayed. If a restart is required at the end of Setup, a dialog box will be presented to the user with a timer warning that the computer will restart in 30 seconds.
/quiet Quiet mode. This is the same as unattended mode, but no status or error messages are displayed.
Restart Options
/norestart Does not restart when installation has completed.
/forcerestart Restarts the computer after installation and force other applications to close at shutdown without saving open files first.
/warnrestart[:x] Presents a dialog box with a timer warning the user that the computer will restart in x seconds. (The default setting is 30 seconds.) Intended for use with the /quiet switch or the /passive switch.
/promptrestart Displays a dialog box prompting the local user to allow a restart.
Special Options
/overwriteoem Overwrites OEM files without prompting.
/nobackup Does not back up files needed for uninstall.
/forceappsclose Forces other programs to close when the computer shuts down.
/log:path Allows the redirection of installation log files.
/integrate:path Integrates the update into the Windows source files. These files are located at the path that is specified in the switch.
/extract[:path] Extracts files without starting the Setup program.
/ER Enables extended error reporting.
/verbose Enables verbose logging. During installation, creates %Windir%\CabBuild.log. This log details the files that are copied. Using this switch may cause the installation to proceed more slowly.

Note You can combine these switches into one command. For backward compatibility, the security update also supports many of the setup switches that the earlier version of the Setup program uses. For more information about the supported installation switches, see Microsoft Knowledge Base Article 262841.

Removing the Update

This security update supports the following setup switches.

Supported Spuninst.exe Switches
SwitchDescription
/help Displays the command-line options.
Setup Modes
/passive Unattended Setup mode. No user interaction is required, but installation status is displayed. If a restart is required at the end of Setup, a dialog box will be presented to the user with a timer warning that the computer will restart in 30 seconds.
/quiet Quiet mode. This is the same as unattended mode, but no status or error messages are displayed.
Restart Options
/norestart Does not restart when installation has completed.
/forcerestart Restarts the computer after installation and force other applications to close at shutdown without saving open files first.
/warnrestart[:x] Presents a dialog box with a timer warning the user that the computer will restart in x seconds. (The default setting is 30 seconds.) Intended for use with the /quiet switch or the /passive switch.
/promptrestart Displays a dialog box prompting the local user to allow a restart.
Special Options
/forceappsclose Forces other programs to close when the computer shuts down.
/log:path Allows the redirection of installation log files.

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 click Search.
    2. In the Search Results pane, click All files and folders under Search Companion.
    3. In the All or part of the file name box, type a file name from the appropriate file information table, and then click Search.
    4. In the list of files, right-click a file name from the appropriate file information table, and then click Properties.

      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.
    5. On the Version tab, determine the version of the file that is installed on your system by comparing it to the version that is documented in the appropriate file information table.

      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.
  • Registry Key Verification

    You may also be able to verify the files that this security update has installed by reviewing the registry keys listed in the Reference Table in this section.

    These registry keys may not contain a complete list of installed files. Also, these registry keys may not be created correctly when an administrator or an OEM integrates or slipstreams this security update into the Windows installation source files.

Other Information

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 (February 8, 2011): Bulletin published.

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