Microsoft Windows contains a vulnerability that could allow an unauthenticated, remote attacker to conduct spoofing attacks by authenticating against a protected server as the targeted user. Updated software is available.
Description
Microsoft Windows contains a vulnerability that could allow an unauthenticated, remote attacker to conduct spoofing attacks.
The vulnerability is due to an error in the Secure Channel (SChannel) security package in Windows. The SChannel authentication component fails to properly handle key exchange data during a Transport Layer Security (TLS) handshake. An attacker who has access to a targeted user's public component of the actual certificate could exploit this vulnerability to authenticate against a protected server as the targeted user.
Microsoft has confirmed the vulnerability and released updated software.
Warning Indicators
The following Microsoft systems are vulnerable:
Windows 2000 SP4 and prior
Windows XP SP3 and prior
Windows XP Professional x64 Edition SP2 and prior
Windows Server 2003 SP2 and prior
Windows Server 2003 x64 Edition SP2 and prior
Windows Vista SP1 and prior
Windows Vista x64 Edition SP1 and prior
Windows Server 2008 for 32-bit Systems
Windows Server 2008 for x64-based Systems
Windows Server 2008 for Itanium-based Systems
IntelliShield Analysis
To exploit this vulnerability, an attacker must have access to the public component of the actual certificate being used by the targeted user, such as the user's public key. Depending on the keypair type, this key may be available as part of key exchange services. If the public component is not publicly available, the attacker may require the use of another attack vector to obtain the user's public key. After the attacker acquires the public component of the certificate, the attacker must then craft a TLS packet in such a way as to bypass the validation process of the SChannel authentication component. Successful exploitation could allow the attacker to impersonate the targeted user and authenticate against a protected server using only the public
component of the user's authentication.
Systems primarily at risk are those that use certificate-based authentication and require the user's corresponding private key during the authentication process. In cases where certificates are used for client authentication, such as web authentication or SSL connections to an Internet Information Services (IIS) web server, the public key is not widely deployed. However, the public key is widely deployed in cases where certificates are used for client authentication and other purposes simultaneously, such as e-mail signing and authentication against multiple websites. It should also be noted that customers who map certificate-authenticated users of their application against an Active directory domain are not affected by this vulnerability. Only locally configured accounts, rather than domain users, are vulnerable to exploitation.
The Cisco Applied Intelligence team has created an Applied Mitigation Bulletin to address vulnerabilities that Microsoft disclosed in the March 2009 security bulletin release. This Cisco bulletin, which assists administrators in identifying or mitigating these vulnerabilities using Cisco devices, is available at the following link: Cisco Applied Mitigation Bulletin: Microsoft Security Bulletin Release for March 2009
Microsoft has corrected this vulnerability by improving the way the server handles key exchange data during the TLS handshake.
Vendor Announcements
Microsoft has released a security bulletin at the following link: MS09-007
Impact
An unauthenticated, remote attacker could exploit this vulnerability to authenticate against a protected server using only the public component of the targeted user's authentication credentials. This action allows the attacker to impersonate the exploited user.
Technical Information
The vulnerability exists because the SChannel authentication component does not perform proper validation on certain TLS handshake messages to ensure the client has access to the authorized user's private key that is linked to the certificate used for authentication.
An unauthenticated, remote attacker who has access to the targeted user's public component of the actual certificate, such as the public key, could exploit this vulnerability to conduct spoofing attacks. The attacker could craft a TLS packet to bypass the SChannel authentication component's validation process. An exploit could allow the attacker to authenticate against a protected server using only the digital certificate and without the associated private key.
Safeguards
Administrators are advised to apply the appropriate updates.
Administrators may consider implementing Active Directory certificate mapping.
Administrators may consider creating new certificates or keypairs for exposed services.
Users are advised to limit the dissemination of public keys for certificates used for authentication.
Patches/Software
Microsoft customers can obtain updates directly by using the links in the MS09-007 security bulletin. These updates are also distributed by Windows automatic update features and available on the Windows Update website. Microsoft Windows Server Update Services (WSUS), Systems Management Server, and System Center Configuration Manager can assist administrators in deploying software updates.
Datacenter Edition Base | Datacenter Edition, 64-bit Base | Enterprise Edition Base | Enterprise Edition, 64-bit Base | Itanium-Based Systems Edition Base | Standard Edition Base | Standard Edition, 64-bit Base | Web Server Base | Web Server, 64-bit Base
Microsoft, Inc.
Windows Vista
Business Base, SP1 | Business x64 Edition Base, SP1 | Enterprise Base, SP1 | Enterprise x64 Edition Base, SP1 | Home Basic Base, SP1 | Home Basic x64 Edition Base, SP1 | Home Premium Base, SP1 | Home Premium x64 Edition Base, SP1 | Ultimate Base, SP1 | Ultimate x64 Edition Base, SP1
Microsoft, Inc.
Windows XP
Home Edition Base, SP1, SP2, SP3 | Professional Edition Base, SP1, SP2, SP3 | Professional x64 (AMD/EM64T) Base, SP2
Associated Products:
N/A
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