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  Microsoft Security Bulletin MS10-049 - Critical Vulnerabilities in SChannel could allow Remote Code Execution (980436)

From:MICROSOFT <secure_(at)_microsoft.com>
Date:10.03.2009
Subject:Microsoft Security Bulletin MS09-007 - Important Vulnerability in SChannel Could Allow Spoofing (960225)

Microsoft Security Bulletin MS09-007 - Important
Vulnerability in SChannel Could Allow Spoofing (960225)
Published: March 10, 2009

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 spoofing if an attacker gains access to the certificate used by the end user for authentication. Customers are only affected when the public key component of the certificate used for authentication has been obtained by the attacker through other means.

This security update is rated Important for all supported editions of Microsoft Windows 2000, Windows XP, Windows Server 2003, Windows Vista, and Windows Server 2008. For more information, see the subsection, Affected and Non-Affected Software, in this section.

The security update addresses the vulnerability by modifying the way that the server parses key exchange data during the TLS handshake. 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 294781.

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.

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

Microsoft Windows 2000 Service Pack 4


Spoofing


Important


MS07-031

Windows XP Service Pack 2


Spoofing


Important


MS07-031

Windows XP Service Pack 3


Spoofing


Important


None

Windows XP Professional x64 Edition and Windows XP Professional x64 Edition Service Pack 2


Spoofing


Important


MS07-031

Windows Server 2003 Service Pack 1 and Windows Server 2003 Service Pack 2


Spoofing


Important


MS07-031

Windows Server 2003 x64 Edition and Windows Server 2003 x64 Edition Service Pack 2


Spoofing


Important


MS07-031

Windows Server 2003 with SP1 for Itanium-based Systems and Windows Server 2003 with SP2 for Itanium-based Systems


Spoofing


Important


MS07-031

Windows Vista and Windows Vista Service Pack 1


Spoofing


Important


None

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


Spoofing


Important


None

Windows Server 2008 for 32-bit Systems*


Spoofing


Important


None

Windows Server 2008 for x64-based Systems*


Spoofing


Important


None

Windows Server 2008 for Itanium-based Systems


Spoofing


Important


None

*Windows Server 2008 server core installation affected. For supported editions of Windows Server 2008, this update applies, with the same severity rating, whether or not Windows Server 2008 was installed using the Server Core installation option. For more information on this installation option, see Server Core. Note that the Server Core installation option does not apply to certain editions of Windows Server 2008; see Compare Server Core Installation Options.
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Frequently Asked Questions (FAQ) Related to This Security Update

Where are the file information details?
The file information details can be found in Microsoft Knowledge Base Article 960225.

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

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

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

Severity Ratings and Vulnerability Identifiers

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 March bulletin summary. For more information, see Microsoft Exploitability Index.
Vulnerability Severity Rating and Maximum Security Impact by Affected Software
Affected Software SChannel Spoofing Vulnerability - CVE-2009-0085 Aggregate Severity Rating

Microsoft Windows 2000 Service Pack 4


Important
Spoofing


Important

Windows XP Service Pack 2 and Windows XP Service Pack 3


Important
Spoofing


Important

Windows XP Professional x64 Edition and Windows XP Professional x64 Edition Service Pack 2


Important
Spoofing


Important

Windows Server 2003 Service Pack 1 and Windows Server 2003 Service Pack 2


Important
Spoofing


Important

Windows Server 2003 x64 Edition and Windows Server 2003 x64 Edition Service Pack 2


Important
Spoofing


Important

Windows Server 2003 with SP1 for Itanium-based Systems and Windows Server 2003 with SP2 for Itanium-based Systems


Important
Spoofing


Important

Windows Vista and Windows Vista Service Pack 1


Important
Spoofing


Important

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


Important
Spoofing


Important

Windows Server 2008 for 32-bit Systems*


Important
Spoofing


Important

Windows Server 2008 for x64-based Systems*


Important
Spoofing


Important

Windows Server 2008 for Itanium-based Systems


Important
Spoofing


Important

*Windows Server 2008 server core installation affected. For supported editions of Windows Server 2008, this update applies, with the same severity rating, whether or not Windows Server 2008 was installed using the Server Core installation option. For more information on this installation option, see Server Core. Note that the Server Core installation option does not apply to certain editions of Windows Server 2008; see Compare Server Core Installation Options.
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SChannel Spoofing Vulnerability - CVE-2009-0085

A spoofing vulnerability exists in the Microsoft Windows SChannel authentication component when using certificate based authentication. An attacker who successfully exploited this vulnerability would be able to authenticate to a server using only an authorized user’s digital certificate and without the associated private key.

To view this vulnerability as a standard entry in the Common Vulnerabilities and Exposures list, see CVE-2009-0085.

Mitigating Factors for SChannel Spoofing Vulnerability - CVE-2009-0085

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:


Customers are only affected when the certificate used for authentication has already been disclosed to the attacker through other means. In the case of an IIS web server, certificates are not transferred in clear text during the authentication process.


Only locally configured user accounts are vulnerable. Customers who map certificate-authenticated users of their application against an Active Directory domain are not affected by this vulnerability.
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Workarounds for SChannel Spoofing Vulnerability - CVE-2009-0085

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:


Customers can implement Active Directory certificate mapping, which is not affected by this vulnerability. Active Directory certificate mapping enables a user with a trusted public key to access domain resources without typing a user name and a password. A client certificate can be directly mapped to an Active Directory user account.

For more information on the different ways of configuring certificate mapping, see Map certificates to user accounts.
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FAQ for SChannel Spoofing Vulnerability - CVE-2009-0085

What is the scope of the vulnerability?
A spoofing vulnerability exists in the Microsoft Windows SChannel authentication component when using certificate based authentication. An attacker who successfully exploited this vulnerability could impersonate another user and authenticate against a protected server using the public component of the user’s authentication credential.

What causes the vulnerability?
The SChannel authentication component does not apply sufficient validation of certain Transport Layer Security (TLS) handshake messages to ensure that the client does in fact have access to the private key linked to the certificate used for authentication.

What is the Secure Channel (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 about SChannel, visit the SChannel web site on MSDN.

What is an x.509 digital certificate?
Encryption techniques using public and private keys require a public-key infrastructure (PKI) to support the distribution and certification of public keys. Digital certificates package public keys, information about the algorithms used, owner or subject data, the digital signature of a Certificate Authority that has verified the subject data, and a date range during which the certificate can be considered valid.

Digital certificates can be validated by a client such as Internet Explorer to ensure that the server to which a user is connecting is in fact the legitimate server for that host name. However, certificates can also be used as a security credential for user authentication and authorization.

What is the Microsoft Secure Sockets Library?
The Microsoft Secure Sockets Layer library contains support for a number of secure communication protocols. These include Transport Layer Security 1.0 (TLS 1.0), Secure Sockets Layer 3.0 (SSL 3.0), the older and seldom-used Secure Sockets Layer 2.0 (SSL 2.0), and Private Communication Technology 1.0 (PCT 1.0) protocol.

These protocols provide an encrypted connection between a server and a client system. SSL can help protect information when users connect across public networks such as the Internet. SSL support requires an SSL certificate, which must be installed on a server. For more information about SSL, see XADM: How Secure Sockets Layer Works.

What is a TLS handshake?
The Transport Layer Security (TLS) Handshake Protocol is responsible for the authentication and key exchange necessary to establish or resume secure sessions. When establishing a secure session, the Handshake Protocol manages the following:


Cipher suite negotiation


Authentication of the server and optionally, the client


Session key information exchange

What is a Security Support Provider (SSP)?
A Security Support Provider implements a common interface between transport-level applications, such as Microsoft Remote Procedure Call (RPC), and security providers, such as Windows Distributed Security. It does this by making one or more security packages available to applications. Each security package provides mappings between an application's security support provider interface function calls and an actual security protocol’s functions. Security packages support security protocols such as Kerberos authentication and the Microsoft LAN Manager.

What might an attacker use the vulnerability to do?
An attacker could use this vulnerability to authenticate against a protected server and impersonate an authorized user, despite not having access to the authorized user’s private key, which is normally required for successful authentication when the server is configured to require client authentication.

How could an attacker exploit the vulnerability?
An attacker would need to gain access to the public component of the actual certificate used by the end user for authentication. He could then craft a Transport Layer Security (TLS) packet to bypass the validation the SChannel component applies to ensure that the private key is in fact present during authentication.

In the most common deployments, certificates used for client authentication have only a single intended purpose configured in a Windows client. These certificates are only transferred for one specific purpose, such as web authentication. In the case of an SSL connection to an Internet Information Services (IIS) web server, the public key is never transferred in cleartext. However, in instances where a single certificate is used for client authentication and other purposes simultaneously, such as in the case of the signing of e-mail, or the certificate is used to authenticate against multiple web sites, the public key may be more widely distributed.

What systems are primarily at risk from the vulnerability?
This vulnerability affects services such as web servers that use certificate based authentication and require the user to prove their possession of the certificate's corresponding private key during the authentication process.

What does the update do?
The update removes the vulnerability by modifying the way that the server parses key exchange data during the TLS handshake.

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

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

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


Secretaria da Fazenda do Estado do Rio Grande do Sul for reporting the SChannel Spoofing Vulnerability (CVE-2009-0085)


Cia de Processamento de Dados do Estado do Rio Grande do Sul for reporting the SChannel Spoofing Vulnerability (CVE-2009-0085)
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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 Microsoft Product Support Services at 1-866-PCSAFETY. There is no charge for support calls that are associated with security updates.


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.
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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 (March 10, 2009): Bulletin published.

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