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HistoryJun 13, 2006 - 12:00 a.m.

Microsoft Security Bulletin MS06-021

2006-06-1300:00:00

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Microsoft Security Bulletin MS06-021
Cumulative Security Update for Internet Explorer (916281)
Published: June 13, 2006

Version: 1.0
Summary

Who should read this document: Customers who use Microsoft Windows

Impact of Vulnerability: Remote Code Execution

Maximum Severity Rating: Critical

Recommendation: Customers should apply the update immediately.

Security Update Replacement: This bulletin replaces several prior security updates. See the frequently asked questions (FAQ) section of this bulletin for the complete list.

Caveats: Microsoft Knowledge Base Article 916281 documents the currently known issues that customers may experience when they install this security update. The article also documents recommended solutions for these issues. For more information, see Microsoft Knowledge Base Article 916281.
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Microsoft is releasing an additional security update included with Microsoft Security Bulletin MS06-023: Vulnerability in Microsoft JScript Could Allow Remote Code Execution (917344). We recommend that you install both security updates at the same time as an update in Microsoft Security Bulletin MS06-021: Cumulative Security Update for Internet Explorer (916281) could expose the JScript vulnerability or cause application compatibility issues.
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This security update also replaces the cumulative update for Internet Explorer that was released on February 28, 2006. For more information about this update, see Microsoft Knowledge Base Article 912945.
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This security update also replaces the compatibility patch released on April 11, 2006. That compatibility patch temporarily returned Internet Explorer to the previous functionality for handling ActiveX controls, to help enterprise customers who needed more time to prepare for the ActiveX update changes discussed in Microsoft Knowledge Base Article 912945. This security update replaces that compatibility patch, and makes the changes in Microsoft Knowledge Base Article 912945 permanent. For more information about these changes, see Microsoft Knowledge Base Article 912945 and the product documentation.

Tested Software and Security Update Download Locations:

Affected Software:
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Microsoft Windows 2000 Service Pack 4
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Microsoft Windows XP Service Pack 1 and Microsoft Windows XP Service Pack 2
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Microsoft Windows XP Professional x64 Edition
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Microsoft Windows Server 2003 and Microsoft Windows Server 2003 Service Pack 1
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Microsoft Windows Server 2003 for Itanium-based Systems and Microsoft Windows Server 2003 with SP1 for Itanium-based Systems
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Microsoft Windows Server 2003 x64 Edition
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Microsoft Windows 98, Microsoft Windows 98 Second Edition (SE), and Microsoft Windows Millennium Edition (Me) — Review the FAQ section of this bulletin for details about these operating systems.

Tested Microsoft Windows Components:

Affected Components:
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Internet Explorer 5.01 Service Pack 4 on Microsoft Windows 2000 Service Pack 4 — Download the update
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Internet Explorer 6 Service Pack 1 on Microsoft Windows 2000 Service Pack 4 or on Microsoft Windows XP Service Pack 1 — Download the update
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Internet Explorer 6 for Microsoft Windows XP Service Pack 2 — Download the update
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Internet Explorer 6 for Microsoft Windows Server 2003 and Microsoft Windows Server 2003 Service Pack 1 — Download the update
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Internet Explorer 6 for Microsoft Windows Server 2003 for Itanium-based Systems and Microsoft Windows Server 2003 with SP1 for Itanium-based Systems — Download the update
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Internet Explorer 6 for Microsoft Windows Server 2003 x64 Edition — Download the update
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Internet Explorer 6 for Microsoft Windows XP Professional x64 Edition — Download the update
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Internet Explorer 6 Service Pack 1 on Microsoft Windows 98, on Microsoft Windows 98 SE, or on Microsoft Windows Millennium Edition — Review the FAQ section of this bulletin for details about this version.

The software in this list has been tested to determine whether the versions are affected. Other versions either no longer include security update support or may not be affected. To determine the support life cycle for your product and version, visit the Microsoft Support Lifecycle Web site.

Note The security updates for Microsoft Windows Server 2003, Windows Server 2003 Service Pack 1, and Windows Server 2003 x64 Edition also apply to Windows Server 2003 R2.
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General Information

Executive Summary

Executive Summary:

This update resolves several newly discovered, publicly and privately reported vulnerabilities. Each vulnerability is documented in its own “Vulnerability Details” section of this bulletin.

If a user is logged on with administrative user rights, an attacker who successfully exploited the most severe of these vulnerabilities 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.

We recommend that customers apply the update immediately.

Severity Ratings and Vulnerability Identifiers:
Vulnerability Identifiers Impact of Vulnerability Internet Explorer 5.0 Service Pack 4 Internet Explorer 6 Service Pack 1 (all supported operating system versions earlier than Windows Server 2003) Internet Explorer 6 for Windows Server 2003 Internet Explorer 6 for Windows Server 2003 Service Pack 1 Internet Explorer 6 for Windows XP Service Pack 2

Exception Handling Memory Corruption Vulnerability - CVE-2006-2218

Remote Code Execution

Critical

HTML Decoding Memory Corruption Vulnerability - CVE-2006-2382

Remote Code Execution

Critical

ActiveX Control Memory Corruption Vulnerability - CVE-2006-2383

Remote Code Execution

Critical

Moderate

Critical

COM Object Instantiation Memory Corruption Vulnerability - CVE-2006-1303

Remote Code Execution

Critical

Moderate

Critical

CSS Cross-Domain Information Disclosure Vulnerability - CVE-2005-4089

Information Disclosure

Important

Moderate

Important

Address Bar Spoofing Vulnerability - CVE-2006-2384

Spoofing and Information Disclosure

Important

Moderate

Important

MHT Memory Corruption Vulnerability - CVE-2006-2385

Remote Code Execution

Moderate

Address Bar Spoofing Vulnerability - CVE-2006-1626

Spoofing

Moderate

Low

Moderate

Aggregate Severity of All Vulnerabilities

Critical

This assessment is based on the types of systems that are affected by the vulnerability, their typical deployment patterns, and the effect that exploiting the vulnerability would have on them.

Note By default, Internet Explorer on Windows Server 2003 runs in a restricted mode that is known as Enhanced Security Configuration. This mode mitigates some of the vulnerabilities. See the FAQ section for this security update for more information about Internet Explorer Enhanced Security Configuration.

Note The severity ratings for non-x86 operating system versions map to the x86 operating systems versions as follows:
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The Microsoft Windows XP Professional x64 Edition severity rating is the same as the Windows XP Service Pack 2 severity rating.
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The Microsoft Windows Server 2003 for Itanium-based Systems severity rating is the same as the Windows Server 2003 severity rating.
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The Microsoft Windows Server 2003 with SP1 for Itanium-based Systems severity rating is the same as the Windows Server 2003 Service Pack 1 severity rating.
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The Microsoft Windows Server 2003 x64 Edition severity rating is the same as the Windows Server 2003 Service Pack 1 severity rating.
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Frequently Asked Questions (FAQ) Related to This Security Update

What updates does this release replace?
This security update replaces several prior security updates. The most recent security bulletin ID and affected operating systems are listed in the following table.
Bulletin ID Internet Explorer 5.01 Service Pack 4 Internet Explorer 6 Service Pack 1 (all versions earlier than Windows Server 2003) Internet Explorer 6 for Windows Server 2003 Internet Explorer 6 for Windows Server 2003 Service Pack 1 Internet Explorer 6 for Windows XP Service Pack 2

MS06-013

Replaced

Note This security update also replaces the compatibility patch released on April 11, 2006. That compatibility patch temporarily returned Internet Explorer to the previous functionality for handling ActiveX controls, to help enterprise customers who needed more time to prepare for the ActiveX update changes discussed in Microsoft Knowledge Base Article 912945. This security update replaces that compatibility patch, and makes the changes in Microsoft Knowledge Base Article 912945 permanent. For more information about these changes, see Microsoft Knowledge Base Article 912945 and the product documentation.

What are the known issues that customers may experience when they install this security update?
Microsoft Knowledge Base Article 916281 documents the currently known issues that customers may experience when they install this security update. The article also documents recommended solutions for these issues. For more information, see Microsoft Knowledge Base Article 916281.

Does this update contain any security-related changes to functionality?
Yes. Besides the changes that are listed in the “Vulnerability Details” section of this bulletin, also included are security-related changes that were introduced in previous Internet Explorer bulletins.

After applying this update Internet Explorer will no longer render the ART image file format. This change has been made to help prevent the Internet Explorer process from closing unexpectedly when users view invalidly formed images. The ART format is no longer supported by Internet Explorer. This change does not impact users of AOL Explorer. Microsoft Security Bulletin MS06-022: Vulnerability in ART Image Rendering Could Allow Remote Code Execution (918439) also includes a security update that addresses a vulnerability in the way that ART files are handled. We recommend that users apply both updates.

The update removes the Exception Handling Memory Corruption Vulnerability - CVE-2006-2218 by changing the way that Internet Explorer does exception handling. Specifically, exception handlers are removed from Internet Explorer with this update. As a result, exceptions from objects that do not handle their own exception, which were previously caught within the Internet Explorer process may now result in application faults. These application faults could cause Internet Explorer to fail. These exception handlers were previously removed from Internet Explorer 7 and Windows Vista. Microsoft Security Bulletin MS06-023: Vulnerability in Microsoft JScript Could Allow Remote Code Execution (917344) addresses the cause of the application fault in JScript discovered while addressing the Exception Handling Memory Corruption Vulnerability. For more information about this change, see the “FAQ for Exception Handling Memory Corruption Vulnerability - CVE-2006-2218” section in this security bulletin.

Does this update contain any other changes to functionality?
Yes. Besides the changes that are listed in the “Vulnerability Details” section of this bulletin, there are also changes not related to security that were introduced in previous Internet Explorer bulletins.

This security update also replaces the compatibility patch released on April 11, 2006. That compatibility patch temporarily returned Internet Explorer to the previous functionality for handling ActiveX controls, to help enterprise customers who needed more time to prepare for the ActiveX update changes discussed in Microsoft Knowledge Base Article 912945 . This security update replaces that compatibility patch, and makes the changes in Microsoft Knowledge Base Article 912945 permanent. For more information about these changes, see Microsoft Knowledge Base Article 912945 and the product documentation.

The changes were first introduced in updates for Windows XP Service Pack 2, Windows Server 2003 Service Pack 1, Windows XP Professional x64 Edition, Windows Server 2003 x64 Edition family, and Windows Server 2003 with Service Pack 1 for Itanium-based Systems on February 28, 2006. For more information about this update, see Microsoft Knowledge Base Article 912945.

The changes were also included in Microsoft Security Bulletin MS06-013: Cumulative Security Update for Internet Explorer (912812) for the same versions of Windows.

This update modifies proxy autoconfiguration functionality to ensure that scripted hostname comparison operations yield expected results.

What is the Internet Explorer Enhanced Security Configuration?
Internet Explorer Enhanced Security Configuration is a group of preconfigured Internet Explorer settings that reduce the likelihood of a user or of an administrator downloading and running specially crafted Web content on a server. Internet Explorer Enhanced Security Configuration reduces this risk by modifying many security-related settings. This includes the settings on the Security tab and the Advanced tab in the Internet Options dialog box. Some of the important modifications include the following:
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Security level for the Internet zone is set to High. This setting disables scripts, ActiveX controls, Microsoft Java Virtual Machine (MSJVM), and file downloads.
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Automatic detection of intranet sites is disabled. This setting assigns all intranet Web sites and all Universal Naming Convention (UNC) paths that are not explicitly listed in the Local intranet zone to the Internet zone.
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Install On Demand and non-Microsoft browser extensions are disabled. This setting prevents Web pages from automatically installing components and prevents non-Microsoft extensions from running.
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Multimedia content is disabled. This setting prevents music, animations, and video clips from running.

How does the extended support for Windows 98, Windows 98 Second Edition, and Windows Millennium Edition affect the release of security updates for these operating systems?
Microsoft will only release security updates for critical security issues. Non-critical security issues are not offered during this support period. For more information about the Microsoft Support Lifecycle policies for these operating systems, visit the following Web site.

For more information about severity ratings, visit the following Web site.

Are Windows 98, Windows 98 Second Edition, or Windows Millennium Edition critically affected by one or more of the vulnerabilities that are addressed in this security bulletin?
Yes. Windows 98, Windows 98 Second Edition, and Windows Millennium Edition are critically affected by the vulnerabilities that are addressed in this security bulletin. Critical security updates for these platforms are available, are provided as part of this security bulletin, and can be downloaded only from the Windows Update Web site. For more information about severity ratings, visit the following Web site.

Extended security update support for Microsoft Windows NT Workstation 4.0 Service Pack 6a and Windows 2000 Service Pack 2 ended on June 30, 2004. Extended security update support for Microsoft Windows NT Server 4.0 Service Pack 6a ended on December 31, 2004. Extended security update support for Microsoft Windows 2000 Service Pack 3 ended on June 30, 2005. I am still using one of these operating systems, what should I do?
Windows NT Workstation 4.0 Service Pack 6a, Windows NT Server 4.0 Service Pack 6a, Windows 2000 Service Pack 2, and Windows 2000 Service Pack 3 have reached the end of their life cycles. It should be a priority for customers who have these operating system versions to migrate to supported versions to prevent potential exposure to vulnerabilities. For more information about the Windows Product Lifecycle, visit the following Microsoft Support Lifecycle Web site. For more information about the extended security update support period for these operating system versions, visit the Microsoft Product Support Services Web site.

Customers who require custom support for these products must contact their Microsoft account team representative, their Technical Account Manager, or the appropriate Microsoft partner representative for custom support options. Customers without an Alliance, Premier, or Authorized Contract can contact their local Microsoft sales office. For contact information, visit the Microsoft Worldwide Information Web site, select the country, and then click Go to see a list of telephone numbers. When you call, ask to speak with the local Premier Support sales manager. For more information, see the Windows Operating System Product Support Lifecycle FAQ.

I am still using Windows NT Server 4.0 Service Pack 6a or Windows NT Server 4.0 Terminal Server Edition Service Pack 6 but extended security update support ended on December 31st, 2004. However, this bulletin has a security update for this operating system version. Why is that?
Windows NT Server 4.0 Service Pack 6a and Windows NT Server 4.0 Terminal Server Edition Service Pack 6 reached the end of their life cycles on December 31, 2004. On this rare occasion, we believe that this vulnerability presents a serious risk to a broad number of customers. We have previously communicated that we reserve the right to produce updates in these situations. We determined that the best course of action to help protect customers was to release this security update. Therefore, we have decided to release a security update for this operating system version as part of this security bulletin. However, because Windows NT Server 4.0 is no longer in support, this security update will only be available on the Microsoft Download Center and will not be available through Windows Update.

We do not anticipate doing this for future vulnerabilities that may affect this operating system version, but as mentioned previously, we reserve the right to produce updates and to make these updates available when necessary. It should be a priority for customers who have this operating system version to migrate to supported operating system versions to prevent potential exposure to vulnerabilities. For more information about the Windows Service Pack Product Life Cycle, visit the Microsoft Support Lifecycle Web site. For more information about the Windows Product Life Cycle, visit the Microsoft Support Lifecycle Web site.

For more information, visit the Windows Operating System FAQ.

Can I use the Microsoft Baseline Security Analyzer (MBSA) to determine whether this update is required?
The following table provides the MBSA detection summary for this security update.
Software MBSA 1.2.1 MBSA 2.0

Microsoft Windows 2000 Service Pack 4

Yes

Microsoft Windows XP Service Pack 1 and Microsoft Windows XP Service Pack 2

Yes

Microsoft Windows XP Professional x64 Edition

Yes

Microsoft Windows Server 2003 and Microsoft Windows Server 2003 Service Pack 1

Yes

Microsoft Windows Server 2003 for Itanium-based Systems and Microsoft Windows Server 2003 with Service Pack 1 for Itanium-based Systems

Yes

Microsoft Windows Server 2003 x64 Edition family

Yes

For more information about MBSA, visit the MBSA Web site. For more information about the software that Microsoft Update and MBSA 2.0 currently do not detect, see Microsoft Knowledge Base Article 895660

Can I use Systems Management Server (SMS) to determine whether this update is required?
The following table provides the SMS detection summary for this security update.
Software SMS 2.0 SMS 2003

Microsoft Windows 2000 Service Pack 4

Yes

Microsoft Windows XP Service Pack 1 and Microsoft Windows XP Service Pack 2

Yes

Microsoft Windows XP Professional x64 Edition

Yes

Microsoft Windows Server 2003 and Microsoft Windows Server 2003 Service Pack 1

Yes

Microsoft Windows Server 2003 for Itanium-based Systems and Microsoft Windows Server 2003 with Service Pack 1 for Itanium-based Systems

Yes

Microsoft Windows Server 2003 x64 Edition family

Yes

SMS uses MBSA for detection. Therefore, SMS has the same limitation that is listed earlier in this bulletin related to software that MBSA does not detect.

For SMS 2.0, the SMS SUS Feature Pack, which includes the Security Update Inventory Tool, can be used by SMS to detect security updates. SMS SUIT uses the MBSA 1.2.1 engine for detection. For more information about the Security Update Inventory Tool, visit the following Microsoft Web site. For more information about the limitations of the Security Update Inventory Tool, see Microsoft Knowledge Base Article 306460. The SMS SUS Feature Pack also includes the Microsoft Office Inventory Tool to detect required updates for Microsoft Office applications.

For SMS 2003, the SMS 2003 Inventory Tool for Microsoft Updates can be used by SMS to detect security updates that are offered by Microsoft Update and that are supported by Windows Server Update Services. For more information about the SMS 2003 Inventory Tool for Microsoft Updates, visit the following Microsoft Web site. SMS 2003 can also use the Microsoft Office Inventory Tool to detect required updates for Microsoft Office applications.

For more information about SMS, visit the SMS Web site.
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Vulnerability Details

Exception Handling Memory Corruption Vulnerability - CVE-2006-2218:

A remote code execution vulnerability exists in the way Internet Explorer handles exceptional conditions. As a result, system memory may be corrupted in such a way that an attacker could execute arbitrary code if a user visited a specially crafted Web site. An attacker who successfully exploited this vulnerability could take complete control of an affected system.

Mitigating Factors for Exception Handling Memory Corruption Vulnerability - CVE-2006-2218:
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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.
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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.
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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, they user could still be vulnerable to this issue through the Web-based attack scenario.

By default, Outlook Express 6, Outlook 2002, and Outlook 2003 open HTML e-mail messages in the Restricted sites zone. Additionally Outlook 2000 opens HTML e-mail messages in the Restricted sites zone if the Outlook E-mail Security Update has been installed. Outlook Express 5.5 Service Pack 2 opens HTML e-mail messages in the Restricted sites zone if Microsoft Security Bulletin MS04-018 has been installed.

Note While it cannot be ruled out that this vulnerability could be used in an exploit without Active Scripting, it significantly increases the chances of a successful exploit. As a result, this vulnerability has been given a severity rating of Critical.
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By default, Internet Explorer on Windows Server 2003 runs in a restricted mode that is known as Enhanced Security Configuration. This mode mitigates this vulnerability in the e-mail vector because reading e-mail messages in plain text is the default configuration for Outlook Express. See the FAQ section for this security update for more information about Internet Explorer Enhanced Security Configuration.
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Workarounds for Exception Handling Memory Corruption Vulnerability - CVE-2006-2218:

Microsoft has tested the following workarounds. While these workarounds will not correct the underlying vulnerability, they help block known attack vectors. When a workaround reduces functionality, it is identified in the following section.

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:

In Internet Explorer, click Internet Options on the Tools menu.

Click the Security tab.

Click Internet, and then click Custom Level.

Under Settings, in the Scripting section, under Active Scripting, click Prompt or Disable, and then click OK.

Click Local intranet, and then click Custom Level.

Under Settings, in the Scripting section, under Active Scripting, click Prompt or Disable, and then click OK.

Click OK two times to 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 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:

In Internet Explorer, click Tools, click Internet Options, and then click the Security tab.

In the Select a Web content zone to specify its current security settings box, click Trusted Sites, and then click Sites.

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.

In the Add this Web site to the zone box, type the URL of a site that you trust, and then click Add.

Repeat these steps for each site that you want to add to the zone.

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 computer. 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.
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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 Microsoft Internet Explorer, follow these steps:

On the Internet Explorer Tools menu, click Internet Options.

In the Internet Options dialog box, click the Security tab, and then click the Internet icon.

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 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”

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

To do this, follow these steps:

In Internet Explorer, click Tools, click Internet Options, and then click the Security tab.

In the Select a Web content zone to specify its current security settings box, click Trusted Sites, and then click Sites.

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.

In the Add this Web site to the zone box, type the URL of a site that you trust, and then click Add.

Repeat these steps for each site that you want to add to the zone.

Click OK two times to accept the changes and return to Internet Explorer.

FAQ for Exception Handling Memory Corruption Vulnerability - CVE-2006-2218:

What is the scope of the vulnerability?
This is a remote code execution vulnerability. An attacker who successfully exploited this vulnerability could remotely 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.

What causes the vulnerability?
Internet Explorer allows objects to register exception handlers that may not properly handle certain conditions. Unsafe exception handling can cause memory corruption resulting in remote code execution.

What might an attacker use the vulnerability to do?
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.

How could an attacker exploit the vulnerability?
An attacker could host a specially crafted Web site that is designed to exploit this vulnerability through Internet Explorer and then persuade a user to view the Web site. This can also include Web sites that accept or host user-provided content or advertisements, and compromised Web sites. These Web sites 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 in an Instant Messenger request that takes users to the attacker's Web site. It could also be possible to display specially crafted Web content by using banner advertisements or by using other methods to deliver Web content to affected systems.

Could this vulnerability be exploited through e-mail?
This vulnerability could not be exploited automatically through e-mail or while viewing e-mail messages in the preview pane while using Outlook or Outlook Express. Customers would have to click a link that would take them to a specially crafted Web site, or open an attachment that could exploit the vulnerability.

What systems are primarily at risk from the vulnerability?
This vulnerability requires a user to be logged on and visiting a Web site for any malicious action to occur. Therefore, any systems where Internet Explorer is used frequently, such as workstations or terminal servers, are at the most risk from this vulnerability.

What does the update do?
The update removes the vulnerability by changing the way that Internet Explorer does exception handling. Specifically, exception handlers are removed from Internet Explorer with this update. These exception handlers were previously removed from Internet Explorer 7 and Windows Vista.

What might the removal of these exception handlers result in?
With the removal of these exception handlers, exceptions from objects that do not handle their own exception, which were previously caught within the Internet Explorer process may now result in application faults. These application faults could cause Internet Explorer to fail. The object or software where the application fault occurs now needs to either address the cause of the application fault or handle its own exception.

What can I do to prevent these application faults?
Microsoft Security Bulletin MS06-023: Vulnerability in Microsoft JScript Could Allow Remote Code Execution (917344) addresses the cause of the application fault in JScript. Other objects, software, or Web application where application faults may occur as a result of the changes made in Microsoft security bulletin MS06-021 now needs to either address the cause of the application fault or handle its own exception.

What is exception handling and how can I implement it?
Robust code anticipates and handles exceptions. Exceptions occur when a program executes abnormally because of conditions outside the program's control. Certain operations, including object creation and file input/output, are subject to failures that go beyond errors. Out-of-memory conditions, for example, can occur even when your program is running correctly. For more information about exception handling see the product documentation:

Exception handling in Visual C++

Exception handling in Visual Basic

Exception handling in the .NET Framework

When this security bulletin was issued, had this vulnerability been publicly disclosed?
No. Microsoft received information about this vulnerability through responsible disclosure.

Note This security update also includes updates for an application fault reported in to us through Microsoft Error Reporting Service. We actively analyze all error reports and prioritize them based on the number of customers affected by the application fault covered in the error report. This application fault is the same as the application fault called out in the public report of the non-exploitable variant of the vulnerability addressed in this security bulletin as “Exception Handling Memory Corruption Vulnerability - CVE-2006-2218”.

This application fault has been discussed as CVE-2006-1992 and a subsequent public post also discussed the exception handling aspect. It is important to note that the application fault in and of itself only will cause Internet Explorer to fail, the vulnerability addressed in this security bulletin must be used for an exploit to occur.

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 and had not seen any examples of proof of concept code published when this security bulletin was originally issued.
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HTML Decoding Memory Corruption Vulnerability - CVE-2006-2382:

A remote code execution vulnerability exists in the way Internet Explorer decodes specially crafted UTF-8 encoded HTML. An attacker could exploit the vulnerability by constructing a specially crafted Web page that could potentially allow remote code execution if a user visited the specially crafted Web site. An attacker who successfully exploited this vulnerability could take complete control of an affected system.

Mitigating Factors for HTML Decoding Memory Corruption Vulnerability - CVE-2006-2382:
•

By default, Internet Explorer on Windows Server 2003 runs in a restricted mode that is known as Enhanced Security Configuration. This mode mitigates this vulnerability in the e-mail vector because reading e-mail messages in plain text is the default configuration for Outlook Express. See the FAQ section of this security update for more information about Internet Explorer Enhanced Security Configuration.
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Workarounds for HTML Decoding Memory Corruption Vulnerability - CVE-2006-2382:

Microsoft has tested the following workarounds. Although these workarounds will not correct the underlying vulnerability, they help block known attack vectors. When a workaround reduces functionality, it is identified in the following section.
•

Read e-mail messages in plain text format if you are using Outlook 2002 or a later version, or Outlook Express 6 SP1 or a later version, to help protect yourself from the HTML e-mail attack vector.

Microsoft Outlook 2002 users who have applied Office XP Service Pack 1 or a later version and Microsoft Outlook Express 6 users who have applied Internet Explorer 6 Service Pack 1 or a later version can enable this setting and view e-mail messages that are not digitally signed or e-mail messages that are not encrypted in plain text only.

Digitally signed e-mail messages or encrypted e-mail messages are not affected by the setting and may be read in their original formats. For more information about how to enable this setting in Outlook 2002, see Microsoft Knowledge Base Article 307594.

For information about this setting in Outlook Express 6, see Microsoft Knowledge Base Article 291387.

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:
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The changes are applied to the preview pane and to open messages.
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Pictures become attachments so that they are not lost.
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Because the message is still in Rich Text or HTML format in the store, the object model (custom code solutions) may behave unexpectedly.
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FAQ for HTML Decoding Memory Corruption Vulnerability - CVE-2006-2382:

What causes the vulnerability?
When Internet Explorer handles specially crafted UTF-8 encoded HTML it may corrupt system memory in such a way that an attacker could execute arbitrary code.

How could an attacker exploit the vulnerability?
An attacker could host a specially crafted Web site or HTML e-mail message that is designed to exploit this vulnerability through Internet Explorer and then persuade a user to view the Web site or HTML e-mail message. This can also include Web sites that accept user-provided content or advertisements, Web sites that host user-provided content or advertisements, and compromised Web sites. These Web sites 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 in an Instant Messenger request that takes users to the attacker's Web site. It could also be possible to display specially crafted Web content by using banner advertisements or by using other methods to deliver Web content to affected systems.

What systems are primarily at risk from the vulnerability?
This vulnerability requires that a user is logged on and reading HTML e-mail messages or that a user is logged on and visits a Web site for any malicious action to occur. Therefore, any systems where HTML e-mail messages are read or where Internet Explorer is used frequently, such as workstations or terminal servers, are at the most risk from this vulnerability.

What does the update do?
The update removes the vulnerability by modifying the way that Internet Explorer decodes UTF-8 encoded HTML.

When this security bulletin was issued, had this vulnerability been publicly disclosed?
No. Microsoft received information about this vulnerability through responsible disclosure.

ActiveX Control Memory Corruption Vulnerability - CVE-2006-2383:

A remote code execution vulnerability exists in the DXImageTransform.Microsoft.Light ActiveX control if passed unexpected data. An attacker could exploit the vulnerability by constructing a specially crafted Web page that could potentially allow remote code execution if a user visited the specially crafted Web site. An attacker who successfully exploited this vulnerability could take complete control of an affected system.

Mitigating Factors for ActiveX Control Memory Corruption Vulnerability - CVE-2006-2383:
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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 messages. However, if a user clicks a link in an e-mail message, the use could still be vulnerable to this issue through the Web-based attack scenario.

Workarounds for ActiveX Control Memory Corruption Vulnerability - CVE-2006-2383:

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:

In Internet Explorer, click Internet Options on the Tools menu.

Click the Security tab.

Click Internet, and then click Custom Level.

Under Settings, in the ActiveX controls and plug-ins section, under Run ActiveX controls and plug-ins, click Prompt or Disable, and then click OK.

Click Local intranet, and then click Custom Level.

Under Settings, in the ActiveX controls and plug-ins section, under Run ActiveX controls and plug-ins, click Prompt or Disable, and then click OK.

Click OK two times to return to Internet Explorer.

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.

To do this, follow these steps:

In Internet Explorer, click Tools, click Internet Options, and then click the Security tab.

In the Select a Web content zone to specify its current security settings box, click Trusted Sites, and then click Sites.

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.

In the Add this Web site to the zone box, type the URL of a site that you trust, and then click Add.

Repeat these steps for each site that you want to add to the zone.

Click OK two times to accept the changes and return to Internet Explorer.

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. You can do this by setting your browser security to High.

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

On the Internet Explorer Tools menu, click Internet Options.

In the Internet Options dialog box, click the Security tab, and then click the Internet icon.

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.

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

To do this, follow these steps:

In Internet Explorer, click Tools, click Internet Options, and then click the Security tab.

In the Select a Web content zone to specify its current security settings box, click Trusted Sites, and then click Sites.

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.

In the Add this Web site to the zone box, type the URL of a site that you trust, and then click Add.

Repeat these steps for each site that you want to add to the zone.

Click OK two times to accept the changes and return to Internet Explorer.

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.

To set the kill bit for the DXImageTransform.Microsoft.Light ActiveX control, 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\{F9EFBEC2-4302-11D2-952A-00C04FA34F05}]
"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:

Group Policy collection

What is Group Policy Object Editor?

Core Group Policy tools and settings

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

Impact of Workaround: The DXImageTransform.Microsoft.Light ActiveX control is a static filter used to create the effect of a light shining on the content of an object. This functionality would no longer be accessible for software using this ActiveX control.
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FAQ for ActiveX Control Memory Corruption Vulnerability - CVE-2006-2383:

What causes the vulnerability?
The DXImageTransform.Microsoft.Light ActiveX control could, if passed unexpected data, cause Internet Explorer to fail in a way that could allow code execution.

How could an attacker exploit the vulnerability?
An attacker could host a specially crafted Web site that is designed to exploit this vulnerability through Internet Explorer and then persuade a user to view the Web site. This can also include Web sites that accept user-provided content or advertisements, Web sites that host user-provided content or advertisements, and compromised Web sites. These Web sites 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 in an Instant Messenger request that takes users to the attacker's Web site. It could also be possible to display specially crafted Web content by using banner advertisements or by using other methods to deliver Web content to affected systems.

What systems are primarily at risk from the vulnerability?
This vulnerability requires that a user is logged on and visits a Web site for any malicious action to occur. Therefore, any systems where Internet Explorer is used frequently, such as workstations or terminal servers, are at the most risk from this vulnerability.

What does the update do?
The update removes the vulnerability by modifying the way that Internet Explorer performs parameter validation.

When this security bulletin was issued, had this vulnerability been publicly disclosed?
No. Microsoft received information about this vulnerability through responsible disclosure.

COM Object Instantiation Memory Corruption Vulnerability - CVE-2006-1303:

A remote code execution vulnerability exists in the way Internet Explorer instantiates COM objects that are not intended to be instantiated in Internet Explorer. An attacker could exploit the vulnerability by constructing a specially crafted Web page that could potentially allow remote code execution if a user visited the specially crafted Web site. An attacker who successfully exploited this vulnerability could take complete control of an affected system.

Mitigating Factors for COM Object Instantiation Memory Corruption Vulnerability - CVE-2006-1303:
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Customers who have installed the security update included with Microsoft Security Bulletin MS05-052 or a later security bulletin for Internet Explorer are not at risk from attacks originating from the Internet 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 messages. However, if a user clicks a link in an e-mail message, 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 mitigates this vulnerability. See the FAQ section for this security update for more information about Internet Explorer Enhanced Security Configuration.
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Workarounds for COM Object Instantiation Memory Corruption Vulnerability - CVE-2006-1303: