IntelliShield has updated this alert to report an increase in intrusion prevention system activity that is related to the Microsoft Windows MHTML protocol handler script execution vulnerability.
Description
Microsoft Windows contains a vulnerability that could allow an unauthenticated, remote attacker to execute arbitrary script in a user's browser session.
The vulnerability is due to improper handling of requests by the Windows MHTML protocol handler. An unauthenticated, remote attacker could exploit the vulnerability by convincing a user to view a malicious website. If successful, the attacker could inject arbitrary script into the user's existing browser session, allowing the attacker to access sensitive browser-based information.
Proof-of-concept code that demonstrates an exploit of this vulnerability is publicly available.
Microsoft has confirmed the vulnerability in a security advisory and released software updates.
Warning Indicators
The following Microsoft systems are affected:
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 Server 2003 with SP2 and prior for Itanium-based Systems
Windows Vista SP2 and prior
Windows Vista x64 Edition SP2 and prior
Windows Server 2008 for 32-bit Systems SP2 and prior
Windows Server 2008 for x64-based Systems SP2 and prior
Windows Server 2008 for Itanium-based Systems SP2 and prior
Windows 7 for 32-bit Systems
Windows 7 for x64-based Systems
Windows Server 2008 R2 for x64-based Systems
Windows Server 2008 R2 for Itanium-based Systems
IntelliShield Analysis
To exploit the vulnerability, an attacker must persuade a user to view a malicious website. The attacker may provide links to a website in e-mail or instant messages delivered to the user. The attacker may use additional social engineering techniques, such as attempting to convince the user that messages originate from a trusted source.
Event data from Cisco Remote Management Services has detected intrusion prevention system signature activity related to this vulnerability. The data, which was captured on April 26, 2011, could indicate that exploits are occurring in the wild.
The Cisco Applied Intelligence team has created an Applied Mitigation Bulletin to address vulnerabilities that Microsoft disclosed in the April 2011 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 April 2011
Vendor Announcements
Microsoft has released a security bulletin at the following link: MS11-026
Microsoft has re-released a security advisory at the following link: 2501696
US-CERT has released a vulnerability note at the following link: VU#326549
Impact
An unauthenticated, remote attacker could exploit this vulnerability to execute arbitrary script in the user's browser session, possibly allowing the attacker to access sensitive information or take actions as the user.
Technical Information
The vulnerability is due to improper handling of Multipurpose Internet Mail Extensions (MIME) requests by the Windows MHTML protocol handler. The protocol handler may improperly run scripts in MIME content in an improper security context.
An unauthenticated, remote attacker could exploit this vulnerability by convincing a user to view a malicious website that contains scripts embedded in MIME-formatted content. When processed, the content could trigger the execution of arbitrary script in the user's browser in a privileged security context that may persist across the browsing session to other sites. The attacker could use the script to monitor user input, spoof content, or take actions as the user on third-party sites.
Safeguards
Administrators are advised to apply the available software updates.
Administrators may consider restricting access to the MHTML protocol handler by applying the fixit solution provided by Microsoft: MHTML Lockdown Fixit
Administrators may consider configuring Internet Explorer to prompt users before running Active Scripting or ActiveX controls by setting the Internet and Local Intranet security zone settings to High. Alternately, administrators could disable Active Scripting and ActiveX controls in these security zones.
Users are advised not to visit websites or follow links that have suspicious characteristics or cannot be verified as safe.
Administrators may consider using the Microsoft Baseline Security Analyzer (MBSA) scan tool to identify common security misconfigurations and missing security updates on system endpoints.
Administrators are advised to implement an intrusion prevention system (IPS) or intrusion detection system (IDS) to help detect and prevent attacks that attempt to exploit this vulnerability.
Administrators are advised to monitor critical systems.
Patches/Software
Microsoft customers can obtain updates directly by using the links in the 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.
Signatures
Cisco Systems Cisco Intrusion Prevention System (IPS) 6.0
Version 6, April 20, 2011, 11:49 AM: IntelliShield has updated this alert to report an increase in intrusion prevention system activity that is related to the Microsoft Windows MHTML protocol handler script execution vulnerability.
Version 5, April 15, 2011, 2:56 PM: IPS signature event data from Cisco Remote Management Services is available for IPS signatures from April 14, 2011.
Version 4, April 12, 2011, 5:58 PM: Microsoft has released a security bulletin and software updates to address the Windows MHTML protocol handler script execution vulnerability.
Version 3, March 14, 2011, 2:49 PM: Microsoft has re-released a security advisory to address the Windows MHTML protocol handler script execution vulnerability.
Version 2, January 31, 2011, 8:57 AM: Proof-of-concept code that demonstrates an exploit of Microsoft Windows MHTML protocol handler script execution vulnerability is publicly available.
Version 1, January 28, 2011, 4:35 PM: Microsoft Windows contains a vulnerability that could allow an unauthenticated, remote attacker to execute arbitrary script in a user's browser session. Updates are not available.
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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