Microsoft Security Bulletin MS10-022 - Important

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:

• 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 convince 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 attacker’s 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.

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:

• 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.

  Impact of workaround. The Windows Help System will be unavailable, and users may not be able to invoke the help function in applications. The attempt to open the Help function in applications may lead to an error message.

  How to undo the workaround.

  Run the following command from an administrative command line:

  echo Y | cacls "%windir%\winhlp32.exe" /E /P everyone
  

  Note You must be logged in as administrator or have administrative credentials to undo 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.

  To raise the browsing security level in Internet Explorer, follow these steps:

  1. On the Internet Explorer Tools menu, click Internet Options.
  2. In the Internet Options dialog box, click the Security tab, and then click the Internet icon.
  3. Under Security level for this zone, move the slider to High. This sets the security level for all Web sites you visit to High.

  Note If no slider is visible, click Default Level, and then move the slider to High.

  Note Setting the level to High may cause some Web sites to work incorrectly. If you have difficulty using a Web site after you change this setting, and you are sure the site is safe to use, you can add that site to your list of trusted sites. This will allow the site to work correctly even with the security setting set to High.

  Impact of workaround. There are side effects to blocking ActiveX Controls and Active Scripting. Many Web sites that are on the Internet or on an intranet use ActiveX or Active Scripting to provide additional functionality. For example, an online e-commerce site or banking site may use ActiveX Controls to provide menus, ordering forms, or even account statements. Blocking ActiveX Controls or Active Scripting is a global setting that affects all Internet and intranet sites. If you do not want to block ActiveX Controls or Active Scripting for such sites, use the steps outlined in "Add sites that you trust to the Internet Explorer Trusted sites zone".

  Add sites that you trust to the Internet Explorer Trusted sites zone

  After you set Internet Explorer to block ActiveX controls and Active Scripting in the Internet zone and in the Local intranet zone, you can add sites that you trust to the Internet Explorer Trusted sites zone. This will allow you to continue to use trusted Web sites exactly as you do today, while helping to protect yourself from this attack on untrusted sites. We recommend that you add only sites that you trust to the Trusted sites zone.

  To do this, follow these steps:

  1. In Internet Explorer, click Tools, click Internet Options, and then click the Security tab.
  2. In the Select a Web content zone to specify its current security settings box, click Trusted Sites, and then click Sites.
  3. If you want to add sites that do not require an encrypted channel, click to clear the Require server verification (https:) for all sites in this zone check box.
  4. In the Add this Web site to the zone box, type the URL of a site that you trust, and then click Add.
  5. Repeat these steps for each site that you want to add to the zone.
  6. Click OK two times to accept the changes and return to Internet Explorer.

  Note Add any sites that you trust not to take malicious action on your system. Two in particular that you may want to add are *.windowsupdate.microsoft.com and *.update.microsoft.com. These are the sites that will host the update, and it requires an ActiveX Control to install the update.

• Configure Internet Explorer to prompt before running Active Scripting or to disable Active Scripting in the Internet and Local intranet security zone

  You can help protect against exploitation of this vulnerability by changing your settings to prompt before running Active Scripting or to disable Active Scripting in the Internet and Local intranet security zone. To do this, follow these steps:

  1. In Internet Explorer, click Tools, click Internet Options, and then click the Security tab.
  2. Click Internet, and then click Custom Level.
  3. Under Settings, in the Scripting section, under Active Scripting, click Prompt or Disable, and then click OK.
  4. Click Local intranet, and then click Custom Level.
  5. Under Settings, in the Scripting section, under Active Scripting, click Prompt or Disable, and then click OK.
  6. Click OK two times to accept the changes and return to Internet Explorer.

  Note Disabling Active Scripting in the Internet and Local intranet security zones may cause some Web sites to work incorrectly. If you have difficulty using a Web site after you change this setting, and you are sure the site is safe to use, you can add that site to your list of trusted sites. This will allow the site to work correctly.

  Impact of workaround. There are side effects to prompting before running Active Scripting. Many Web sites that are on the Internet or on an intranet use Active Scripting to provide additional functionality. For example, an online e-commerce site or banking site may use Active Scripting to provide menus, ordering forms, or even account statements. Prompting before running Active Scripting is a global setting that affects all Internet and intranet sites. You will be prompted frequently when you enable this workaround. For each prompt, if you feel you trust the site that you are visiting, click Yes to run Active Scripting. If you do not want to be prompted for all these sites, use the steps outlined in "Add sites that you trust to the Internet Explorer Trusted sites zone".

  Add sites that you trust to the Internet Explorer Trusted sites zone

  After you set Internet Explorer to block ActiveX controls and Active Scripting in the Internet zone and in the Local intranet zone, you can add sites that you trust to the Internet Explorer Trusted sites zone. This will allow you to continue to use trusted Web sites exactly as you do today, while helping to protect yourself from this attack on untrusted sites. We recommend that you add only sites that you trust to the Trusted sites zone.

  To do this, follow these steps:

  1. In Internet Explorer, click Tools, click Internet Options, and then click the Security tab.
  2. In the Select a Web content zone to specify its current security settings box, click Trusted Sites, and then click Sites.
  3. If you want to add sites that do not require an encrypted channel, click to clear the Require server verification (https:) for all sites in this zone check box.
  4. In the Add this Web site to the zone box, type the URL of a site that you trust, and then click Add.
  5. Repeat these steps for each site that you want to add to the zone.
  6. Click OK two times to accept the changes and return to Internet Explorer.

  Note Add any sites that you trust not to take malicious action on your system. Two in particular that you may want to add are *.windowsupdate.microsoft.com and *.update.microsoft.com. These are the sites that will host the update, and it requires an ActiveX Control to install the update.

What is the scope of the vulnerability? 
This is a remote code execution vulnerability. An attacker who successfully exploited this vulnerability could gain the same user rights as the logged-on user. 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.

What causes the vulnerability? 
The vulnerability exists in the way that VBScript interacts with Windows Help files when using Internet Explorer. While Windows Help Files are inherently unsafe files, the implementation of VBScript on affected systems allows an attacker to specify a Help file location when displaying a dialog box on a Web page. If a visitor pressed the F1 key while such a dialog box is being displayed, this specially crafted Help file could be loaded by the Windows Help System, allowing execution of arbitrary code in the security context of the currently logged-on user.

What is VBScript? 
VBScript (Visual Basic Script) is an interpreted, object-based scripting language that is often used to make Web sites more flexible or interactive. VBScript scripts can run only in the presence of an interpreter or host, such as Active Server Pages (ASP), Internet Explorer, or Windows Script Host. For more information, see the MSDN article VBScript Fundamentals.

What are unsafe file types? 
Microsoft uses the concept of "unsafe file types" to help better protect users from executable content that an attacker could embed in such files. For more information, see the whitepaper Understanding Executable Content in Microsoft Products, and Microsoft Knowledge Base Article 291369.

What is the F1 key? 
F1 is one of the 12 function keys (F1 – F12) on a regular keyboard, typically located in the top row of keys. Function keys allow users to reach certain functions in an application by pressing only a single key on the keyboard. In most applications, F1 would bring up the Help function and many users are familiar with instructions such as "Press F1 for help".

What is defense-in-depth? 
In information security, defense-in-depth refers to an approach in which multiple layers of defense are in place to help prevent attackers from compromising the security of a network or system.

What might an attacker use the vulnerability to do? 
An attacker who successfully exploited this vulnerability could run arbitrary code as the logged-on user. If a user is logged on with administrative user rights, an attacker could take complete control of the affected system.

How could an attacker exploit the vulnerability? 
Successful exploitation of this vulnerability requires that an attacker convince a user to visit a specially crafted Web page that displays a dialog box, and then convince the user to press the F1 key on the keyboard while this dialog box is being displayed.

What systems are primarily at risk from the vulnerability? 
Client, workstation, or terminal server systems where Internet Explorer is used to browse Web pages are primarily at risk.

I am running Internet Explorer on Windows Server 2003 or Windows Server 2008. Does this mitigate this vulnerability? 
By default, Internet Explorer on Windows Server 2003 and Windows Server 2008 runs in a restricted mode that is known as Enhanced Security Configuration, which mitigates this vulnerability. Enhanced Security Configuration is a group of preconfigured settings in Internet Explorer that can reduce the likelihood of a user or administrator downloading and running specially crafted Web content on a server. This is a mitigating factor for Web sites that you have not added to the Internet Explorer Trusted sites zone. See also Managing Internet Explorer Enhanced Security Configuration.

How does configuring the Internet zone security setting to High protect me from this vulnerability? 
Setting the Internet zone security setting to High protects against this vulnerability by disabling Active Scripting, which is required in order to exploit this vulnerability.

Why is this vulnerability not exploitable on Windows Vista, Windows Server 2008, Windows 7, or Windows Server 2008 R2? 
Windows Vista, Windows Server 2008, Windows7, and Windows Server 2008 R2 include architectural improvements in the way that Internet Explorer interacts with the Windows operating system and VBScript. This prevents exploitation of this vulnerability, even though the vulnerable code is present on those systems where users have installed the Windows Help System.

What does the update do? 
This security update addresses the vulnerability by modifying the way that the VBScript engine processes help files in protected mode on affected versions of the Windows operating systems. On Windows Vista, Windows Server 2008, Windows 7, and Windows Server 2008 R2, there is no known attack vector to exploit this vulnerability, but the update can be installed as a defense-in-depth measure.

When this security bulletin was issued, had this vulnerability been publicly disclosed? 
Yes. This vulnerability has been publicly disclosed. It has been assigned Common Vulnerability and Exposure number CVE-2010-0483. This vulnerability was described in Microsoft Security Advisory 981169.

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.

Reference Table

The following table contains the security update information for this software. You can find additional information in the subsection, Deployment Information, in this section.

Reference Table

The following table contains the security update information for this software. You can find additional information in the subsection, Deployment Information, in this section.

Note For supported versions of Windows XP Professional x64 Edition, this security update is the same as supported versions of the Windows Server 2003 x64 Edition security update.

Reference Table

The following table contains the security update information for this software. You can find additional information in the subsection, Deployment Information, in this section.

Reference Table

The following table contains the security update information for this software. You can find additional information in the subsection, Deployment Information, in this section.

Reference Table

The following table contains the security update information for this software. You can find additional information in the subsection, Deployment Information, in this section.

Reference Table

The following table contains the security update information for this software. You can find additional information in the subsection, Deployment Information, in this section.

Reference Table

The following table contains the security update information for this software. You can find additional information in the subsection, Deployment Information, in this section.