===================================================================== CERT-Renater Note d'Information No. 2010/VULN126 _____________________________________________________________________ DATE : 14/04/2010 HARDWARE PLATFORM(S) : / OPERATING SYSTEM(S) : Windows 2000, Windows XP, Windows Server 2003 running VBScript Scripting Engine. ====================================================================== KB981169 http://www.microsoft.com/technet/security/bulletin/ms10-022.mspx ______________________________________________________________________ Microsoft Security Bulletin (981169) Vulnerability in VBScript Scripting Engine Could Allow Remote Code Execution Published: April 13, 2010 Version: 1.0 General Information Executive Summary This security update resolves a publicly disclosed vulnerability in VBScript on Microsoft Windows that could allow remote code execution. This security update is rated Important for Microsoft Windows 2000, Windows XP, and Windows Server 2003. On Windows Server 2008, Windows Vista, Windows 7, and Windows Server 2008 R2, the vulnerable code is not exploitable, however, as the code is present, this update is provided as a defense-in-depth measure and has no severity rating. The vulnerability could allow remote code execution if a malicious Web site displayed a specially crafted dialog box on a Web page and a user pressed the F1 key, causing the Windows Help System to be started with a Windows Help File provided by the attacker. If a user is logged on with administrative user rights, an attacker who successfully exploited this vulnerability could take complete control of an affected system. The security update addresses the vulnerability by modifying the way that the VBScript engine processes help files in protected mode. This security update addresses the vulnerability first described in Microsoft Security Advisory 981169. 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. Affected Software Microsoft Windows 2000 Service Pack 4 Windows XP Service Pack 2 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 Mitigating Factors This vulnerability cannot be exploited on Windows Vista, Windows Server 2008, Windows 7, or Windows Server 2008 R2. This vulnerability requires user interaction. The vulnerability could not be exploited without user interaction even if the user visited a malicious Web site. Instead, an attacker would need to persuade a user to press the F1 key on the keyboard while the Web site displays a scripted dialog box. In a Web-based attack scenario, an attacker could host a Web site that contains a Web page that is used to exploit this vulnerability. In addition, compromised Web sites and Web sites that accept or host user-provided content or advertisements could contain specially crafted content that could exploit this vulnerability. In all cases, however, an attacker would have no way to force users to visit these Web sites. Instead, an attacker would have to convince users to visit the Web site, typically by getting them to click a link in an e-mail message or Instant Messenger message that takes users to the attackers Web site. By default, all supported versions of Microsoft Outlook, Microsoft Outlook Express, and Windows Mail open HTML e-mail messages in the Restricted sites zone, removing the risk of an attacker being able to use this vulnerability to execute malicious code. The Restricted sites zone helps mitigate attacks that could try to exploit this vulnerability by preventing Active Scripting and ActiveX controls from being used when reading HTML e-mail messages. However, if a user clicks a link in an e-mail message, the user could still be vulnerable to exploitation of this vulnerability through the Web-based attack scenario. Additionally, Outlook 2007 uses a different component to render HTML e-mail, removing the risk of this exploit. By default, Internet Explorer on Windows Server 2003 runs in a restricted mode that is known as Enhanced Security Configuration. This mode sets the security level for the Internet zone to High. This is a mitigating factor for Web sites that you have not added to the Internet Explorer Trusted sites zone. An attacker who successfully exploited this vulnerability could gain the same user rights as the local user. Users whose accounts are configured to have fewer user rights on the system could be less affected than users who operate with administrative user rights. Workarounds Do not press the F1 key when prompted by a Web site Successful exploitation of this vulnerability requires that users assist the exploit by pressing the F1 key on their keyboard. Our analysis shows that if users do not press the F1 key on their keyboard, the vulnerability cannot be exploited. Consequently, malicious Web sites may attempt to convince users to press the F1 key. Such a Web site could invoke an endless loop of dialog boxes that tell the user to press the F1 key to end the loop, or offer information such as pricing information or help to be revealed through the F1 key. Users are advised to avoid pressing F1 presented by Web pages or other Internet content. If a dialog box appears repeatedly in an attempt to convince the user to press F1, users may log off the system or use Task Manager to terminate the Internet Explorer process. Restrict access to the Windows Help System Successful exploitation of this vulnerability requires that the Windows Help System is functioning. You can help protect against exploitation of this vulnerability if you modify the ACL on winhlp32.exe to be more restrictive on Windows 2000, Windows XP, and Windows Server 2003 by running the following command from an administrative command line: echo Y | cacls "%windir%\winhlp32.exe" /E /P everyone:N Note You must be logged in as administrator or have administrative credentials to complete this workaround. Set Internet and Local intranet security zone settings to "High" to block ActiveX Controls and Active Scripting in these zones You can help protect against exploitation of this vulnerability by changing your settings for the Internet security zone to block ActiveX controls and Active Scripting. You can do this by setting your browser security to High. Vulnerability Information VBScript Help Keypress Vulnerability - CVE-2010-0483 A remote code execution vulnerability exists in the way that VBScript interacts with Windows Help files when using Internet Explorer. If a malicious Web site displayed a specially crafted dialog box and a user pressed the F1 key, the Windows Help System would be started with a Windows Help File provided by the attacker. If a user is logged on with administrative user rights, an attacker who successfully exploited this vulnerability could take complete control of an affected system. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights. On systems running Windows Server 2003, Internet Explorer Enhanced Security Configuration is enabled by default, which helps to mitigate against this issue. ====================================================================== ========================================================= Les serveurs de référence du CERT-Renater http://www.urec.fr/securite http://www.cru.fr/securite http://www.renater.fr ========================================================= + CERT-RENATER | tel : 01-53-94-20-44 + + 151 bd de l'Hopital | fax : 01-53-94-20-41 + + 75013 Paris | email: certsvp@renater.fr + =========================================================