Microsoft Security Bulletin MS07-033 - Critical

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 persuade 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.

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 impacted than users who operate with administrative user rights.

By default, all supported releases of Microsoft Outlook and Microsoft Outlook Express open HTML e-mail messages in the Restricted sites zone. The Restricted sites zone helps reduce attacks that could try to exploit this vulnerability by preventing ActiveX controls from being used when reading HTML e-mail. However, if a user clicks on a link within an e-mail they could still be vulnerable to this issue through the Web-based attack scenario.

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. See the FAQ section of this security bulletin for more information about Internet Explorer Enhanced Security Configuration.

Internet Explorer 7 is not affected by this vulnerability.

Configure Internet Explorer to prompt before running ActiveX Controls or disable ActiveX Controls in the Internet and Local intranet security zone

You can help protect against this vulnerability by changing your Internet Explorer settings to prompt before running ActiveX controls. To do this, follow these steps:

Impact of Workaround: There are side effects to prompting before running ActiveX controls. Many Web sites that are on the Internet or on an intranet use ActiveX 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. Prompting before running ActiveX controls 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 ActiveX controls. 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 require a prompt before it runs 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 you 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:

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” (without the quotation marks). These are the sites that will host the update, and it requires an ActiveX Control to install the update.

Set Internet and Local intranet security zone settings to “High” to prompt before running ActiveX Controls and Active Scripting in these zones

You can help protect against this vulnerability by changing your settings for the Internet security zone to prompt before running 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:

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 prompting before running 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. Prompting before running ActiveX controls or 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 ActiveX controls or 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”.

Prevent COM objects from running in Internet Explorer

You can disable attempts to instantiate a COM object in Internet Explorer by setting the kill bit for the control in the registry.

Warning If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

For detailed steps that you can use to prevent a control from running in Internet Explorer, see Microsoft Knowledge Base Article 240797. Follow these steps in this article to create a Compatibility Flags value in the registry to prevent a COM object from being instantiated in Internet Explorer.

Note The Class Identifiers and corresponding files where the COM objects are contained are documented provided in the table below

Replace {XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX} below with the Class Identifiers above.

To set the kill bit for a CLSID with a value of {XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX}, paste the following text in a text editor such as Notepad. Then, save the file by using the .reg file name extension.

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\ActiveX Compatibility\{ XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX }]
"Compatibility Flags"=dword:00000400

You can apply this .reg file to individual systems by double-clicking it. You can also apply it across domains by using Group Policy. For more information about Group Policy, visit the following Microsoft Web sites:

Note You must restart Internet Explorer for your changes to take effect.

Impact of Workaround: There is no impact as long as the COM object is not intended to be used in Internet Explorer.

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 or Instant Messenger message that takes users to the attacker's Web site.

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 impacted than users who operate with administrative user rights.

By default, all supported releases of Microsoft Outlook and Microsoft Outlook Express open HTML e-mail messages in the Restricted sites zone. The Restricted sites zone helps reduce the number of successful attacks that exploit this vulnerability by preventing Active Scripting and ActiveX controls from being used when reading HTML e-mail. However, if a user clicks on a link within an e-mail they could still be vulnerable to this issue through the Web-based attack scenario.

Note It cannot be ruled out that this vulnerability could be used in an exploit without Active Scripting. However, using Active Scripting significantly increases the chances of a successful exploit. As a result, this vulnerability has been given a severity rating of Critical on Windows Server 2003.

Internet Explorer 5.01 Service Pack 4 on Windows 2000 Service Pack 4 and Internet Explorer 7 are not affected by this vulnerability.

Read e-mail messages in plain text format to help protect yourself from the HTML e-mail attack vector

You can help protect yourself against this vulnerability by changing your e-mail settings to read e-mail messages in plain text using Outlook 2002 and later, Outlook Express 6 and later, or Windows Mail. For information in Outlook, search “plain text” in Help and review “Read messages in plain text.” In Outlook Express, search “plain text” in Help and review “Reducing your risk of getting e-mail viruses.” In Windows Mail, search “plain text” in Help and review “Security and privacy in Windows Mail.”

Impact of workaround: E-mail messages that are viewed in plain text format will not contain pictures, specialized fonts, animations, or other rich content. Additionally:

User interaction, while expected, is required to exploit this vulnerability.

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.

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 impacted than users who operate with administrative user rights.

Internet Explorer 7 in Windows Vista and Internet Explorer 7 in Windows Vista x64 Edition are not affected by this vulnerability.

Prevent Language Pack Installation

You can prevent language pack installation in Internet Explorer by setting a registry key.

Warning If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

[HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\International]
"W2KLpk"=dword:00000000

You can apply this .reg file to individual systems by double-clicking it. You can also apply it across domains by using Group Policy. For more information about Group Policy, visit the following Microsoft Web sites:

Note You must restart Internet Explorer for your changes to take effect.

Impact of Workaround: No language pack(s) will be installed on demand.

How to undo the workaround:

You can enable language pack installation in Internet Explorer by setting a registry key.

[HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\International]
"W2KLpk"=dword:00000001

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.

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 impacted than users who operate with administrative user rights.

The Restricted sites zone helps reduce attacks that could try to exploit this vulnerability by preventing Active Scripting 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 this issue through the Web-based attack scenario.

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. See the FAQ section of this security update for more information about Internet Explorer Enhanced Security Configuration.

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 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:

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.

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

After you set Internet Explorer to require a prompt before it runs 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 you 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:

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” (without the quotation marks). These are the sites that will host the update, and it requires an ActiveX Control to install the update.

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”.

Set Internet and Local intranet security zone settings to “High” to prompt before running ActiveX Controls and Active Scripting in these zones

You can help protect against this vulnerability by changing your settings for the Internet security zone to prompt before running 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:

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.

User interaction, while expected, is required to exploit this vulnerability.

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.

Internet Explorer 5.01 Service Pack 4 on Windows 2000 Service Pack 4, Internet Explorer 6 Service Pack 1 when installed on Windows 2000 Service Pack 4, and Internet Explorer 6 are not affected by this vulnerability.

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 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:

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 require a prompt before it runs ActiveX controls or 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 you 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:

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.

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 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 or Instant Messenger message that takes users to the attacker's Web site.

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 impacted than users who operate with administrative user rights.

Prevent COM objects from running in Internet Explorer

You can disable attempts to instantiate a COM object in Internet Explorer by setting the kill bit for the control in the registry.

Warning If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

For detailed steps that you can use to prevent a control from running in Internet Explorer, see Microsoft Knowledge Base Article 240797. Follow these steps in this article to create a Compatibility Flags value in the registry to prevent a COM object from being instantiated in Internet Explorer.

Note The Class Identifiers and corresponding files where the COM objects are contained are documented under “What does the update do?” in the “FAQ for Speech Control Memory Corruption Vulnerability - CVE-2007-2222” section. Replace {XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX} below with the Class Identifiers found in this section.

To set the kill bit for a CLSID with a value of {XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX}, paste the following text in a text editor such as Notepad. Then, save the file by using the .reg file name extension.

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\ActiveX Compatibility\{ XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX }]
"Compatibility Flags"=dword:00000400

You can apply this .reg file to individual systems by double-clicking it. You can also apply it across domains by using Group Policy. For more information about Group Policy, visit the following Microsoft Web sites:

Note You must restart Internet Explorer for your changes to take effect.

Impact of Workaround: There is no impact as long as the object is not intended to be used in Internet Explorer.