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From:MICROSOFT <secure_(at)_microsoft.com>
Date:13.10.2010
Subject:Microsoft Security Bulletin MS10-085 - Important Vulnerability in SChannel Could Allow Denial of Service (2207566)

Microsoft Security Bulletin MS10-085 - Important
Vulnerability in SChannel Could Allow Denial of Service (2207566)
Published: October 12, 2010

Version: 1.0
General Information
Executive Summary

This security update resolves a privately reported vulnerability in the Secure Channel (SChannel) security package in Windows. The vulnerability could allow denial of service if an affected Internet Information Services (IIS) server hosting a Secure Sockets Layer (SSL)-enabled Web site received a specially crafted packet message. By default, IIS is not configured to host SSL Web sites.

This security update is rated Important for all supported editions of Windows Vista, Windows Server 2008, Windows 7, and 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 changing the way that IIS processes client certificate 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
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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
Operating System Maximum Security Impact Aggregate Severity Rating Bulletins Replaced by this Update

Windows Vista Service Pack 1 and Windows Vista Service Pack 2


Denial of Service


Important


MS10-049

Windows Vista x64 Edition Service Pack 1 and Windows Vista x64 Edition Service Pack 2


Denial of Service


Important


MS10-049

Windows Server 2008 for 32-bit Systems and Windows Server 2008 for 32-bit Systems Service Pack 2*


Denial of Service


Important


MS10-049

Windows Server 2008 for x64-based Systems and Windows Server 2008 for x64-based Systems Service Pack 2*


Denial of Service


Important


MS10-049

Windows Server 2008 for Itanium-based Systems and Windows Server 2008 for Itanium-based Systems Service Pack 2


Denial of Service


Important


MS10-049

Windows 7 for 32-bit Systems


Denial of Service


Important


MS10-049

Windows 7 for x64-based Systems


Denial of Service


Important


MS10-049

Windows Server 2008 R2 for x64-based Systems*


Denial of Service


Important


MS10-049

Windows Server 2008 R2 for Itanium-based Systems


Denial of Service


Important


MS10-049

*Server Core installation affected. This update applies, with the same severity rating, to supported editions of Windows Server 2008 or Windows Server 2008 R2 as indicated, whether or not 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
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Frequently Asked Questions (FAQ) Related to This Security 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.

Why am I not being offered this security update through Automatic Update?
This security update is offered only to systems that have IIS installed on an operating system listed in the Affected Software table. Systems that are listed in the Affected Software section of this bulletin, but on which IIS is not installed, will not be offered this update through Automatic Update, as this vulnerability can only be exploited when IIS is installed.

If SSL is not enabled on an affected system that has IIS installed, the update will be offered and Microsoft recommends that users install the update. However, the vulnerability is only exploitable when SSL is enabled.
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Vulnerability Information

Severity Ratings and Vulnerability Identifiers

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 October bulletin summary. For more information, see Microsoft Exploitability Index.
Vulnerability Severity Rating and Maximum Security Impact by Affected Software
Affected Software TLSv1 Denial of Service Vulnerability - CVE-2010-3229 Aggregate Severity Rating

Windows Vista Service Pack 1 and Windows Vista Service Pack 2


Important
Denial of Service


Important

Windows Vista x64 Edition Service Pack 1 and Windows Vista x64 Edition Service Pack 2


Important
Denial of Service


Important

Windows Server 2008 for 32-bit Systems and Windows Server 2008 for 32-bit Systems Service Pack 2*


Important
Denial of Service


Important

Windows Server 2008 for x64-based Systems and Windows Server 2008 for x64-based Systems Service Pack 2*


Important
Denial of Service


Important

Windows Server 2008 for Itanium-based Systems and Windows Server 2008 for Itanium-based Systems Service Pack 2


Important
Denial of Service


Important

Windows 7 for 32-bit Systems


Important
Denial of Service


Important

Windows 7 for x64-based Systems


Important
Denial of Service


Important

Windows Server 2008 R2 for x64-based Systems*


Important
Denial of Service


Important

Windows Server 2008 R2 for Itanium-based Systems


Important
Denial of Service


Important

*Server Core installation affected. This update applies, with the same severity rating, to supported editions of Windows Server 2008 or Windows Server 2008 R2 as indicated, whether or not 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.
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TLSv1 Denial of Service Vulnerability - CVE-2010-3229

A denial of service vulnerability exists in the way that SChannel processes client certificates in implementations of Internet Information Services (IIS) 7.0 on Windows Server 2008 and Windows Vista, and in IIS 7.5 on Windows Server 2008 R2 and Windows 7. A remote, anonymous attacker could send a specially crafted network packet to the affected system that would cause the LSASS service to stop responding and the system to restart. Systems are only affected if SSL is enabled, which is not a default configuration.

To view this vulnerability as a standard entry in the Common Vulnerabilities and Exposures list, see CVE-2010-3229.

Mitigating Factors for TLSv1 Denial of Service Vulnerability - CVE-2010-3229

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:


By default, IIS is not configured to accept SSL connections.


The system will automatically restart after a successful attack, allowing the system to recover.
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Workarounds for TLSv1 Denial of Service Vulnerability - CVE-2010-3229

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:


Stop SSL Web sites in IIS

Stop the SSL-enabled Web sites hosted on your IIS server as follows:

1.


Open the Internet Information Services (IIS) Manager.

2.


In the Connections panel on the left, select a Web site that uses SLL.

3.


Click Stop in the right panel.

4.


Repeat steps 2 and 3 for every SSL-enabled Web site.

Impact of workaround. Clients will only be able to access non-SSL Web sites.

How to undo the workaround.

1.


Open the Internet Information Services (IIS) Manager.

2.


In the Connections panel on the left, select a Web site that uses SLL.

3.


Click Start in the right panel.

4.


Repeat steps 2 and 3 for every SSL-enabled Web site.
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FAQ for TLSv1 Denial of Service Vulnerability - CVE-2010-3229

What is the scope of the vulnerability?
This is a denial of service vulnerability. An attacker who exploited the vulnerability could cause the LSASS service to stop and the computer to restart, creating a Denial of Service condition until the system has successfully restarted. An attacker could then exploit the vulnerability again.

What causes the vulnerability?
The vulnerability is caused when SChannel fails to check a logical condition before processing a protocol request during an SSL/TLS handshake.

What is the SChannel security package?
The Secure Channel (SChannel) security package is a Security Support Provider (SSP) that implements the Secure Sockets Layer (SSL) and Transport Layer Security (TLS) Internet standard authentication protocols. These components are used to implement secure communications in support of several common Internet and network applications, such as Web browsing. SChannel is part of the security package that helps provide an authentication service to provide secure communications between client and server.

For more information, see the MSDN article, Secure Channel.

What are TLS and SSL?
The Transport Layer Security (TLS) Handshake Protocol is responsible for the authentication and key exchange necessary to establish or resume secure sessions. The Secure Sockets Layer (SSL) is a predecessor of the Transport Layer Security protocol. Both TLS and SSL perform the same functions and support secure network communications using a combination of public and secret key technology.

For more information, see the TechNet article, How TLS/SSL works.

What is a TLS or SSL handshake?
When establishing a secure session using TLS or SSL, the Handshake Protocol manages the following:


Cipher suite negotiation


Authentication of the server and optionally, the client


Session key information exchange

For more information, see the TechNet article, How TLS/SSL works.

Can I use the "accept client certificates" setting in IIS as a workaround?
No. If your system is running the affected software with SSL enabled, setting the accept client certificates setting in IIS to ignore will not be an effective way to prevent exploitation of this vulnerability.

What might an attacker use the vulnerability to do?
An attacker who successfully exploited this vulnerability could cause a server to stop responding and require a restart.

How could an attacker exploit the vulnerability?
A remote, anonymous attacker could send a specially crafted packet message to an affected IIS server hosting an SSL-enabled Web site, which could cause LSASS to stop responding, resulting in a denial of service.

What systems are primarily at risk from the vulnerability?
This vulnerability affects Web servers on which SSL is enabled.

What does the update do?
The update addresses the vulnerability by changing the way IIS processes client certificate requests.

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.

Other Information
Acknowledgments

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


The Mu Test Suite Team at Mu Dynamics for reporting the TLSv1 Denial of Service Vulnerability (CVE-2010-3229)
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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.
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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 (October 12, 2010): Bulletin published.

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