Microsoft Security Bulletin MS06-046 Vulnerability in HTML Help Could Allow Remote Code Execution (922616)

Microsoft Security Bulletin MS06-046
Vulnerability in HTML Help Could Allow Remote Code Execution (922616)
Published: August 8, 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 a prior security update. See the frequently asked questions (FAQ) section of this bulletin for the complete list.

Caveats: None.

Tested Software and Security Update Download Locations:

Affected Software:
•

Microsoft Windows 2000 Service Pack 4 — Download the update
•

Microsoft Windows XP Service Pack 1 and Microsoft Windows XP Service Pack 2 — Download the update
•

Microsoft Windows XP Professional x64 Edition — Download the update
•

Microsoft Windows Server 2003 and Microsoft Windows Server 2003 Service Pack 1 — Download the update
•

Microsoft Windows Server 2003 for Itanium-based Systems and Microsoft Windows Server 2003 with SP1 for Itanium-based Systems — Download the update
•

Microsoft Windows Server 2003 x64 Edition — Download the update
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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.
General Information

Executive Summary

Executive Summary:

This update resolves a newly discovered, publicly reported vulnerability as well as additional issues discovered through internal investigations. The vulnerability is documented in the "Vulnerability Details" section of this bulletin.

On vulnerable versions of Windows, if a user is logged on with administrative user rights, an attacker who successfully exploited this vulnerability could take complete control of the client workstation. 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 Windows 2000 Windows XP Service Pack 1 Windows XP Service Pack 2 Windows Server 2003 Windows Server 2003 Service Pack 1

Buffer Overrun in HTML Help Vulnerability - CVE-2006-3357

Remote Code Execution

Critical

Critical

Critical

Moderate

Moderate

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 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.

Note The severity ratings for non-x86 operating system versions map to the x86 operating systems versions as follows:
•

The Microsoft Windows XP Professional x64 Edition severity rating is the same as the Windows XP Service Pack 2 severity rating.
•

The Microsoft Windows Server 2003 for Itanium-based Systems severity rating is the same as the Windows Server 2003 severity rating.
•

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.
•

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 a prior security update. The security bulletin ID and affected operating systems are listed in the following table.
Bulletin ID Windows 2000 Windows XP Service Pack 1 Windows XP Service Pack 2 Windows Server 2003 Windows Server 2003 Service Pack 1

MS05-001

Replaced

Replaced

Replaced

Replaced

Replaced

What are the known issues that customers may experience when they install this security update?
Microsoft Knowledge Base Article 922616 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 922616.

Extended security update support for Windows 98, Windows 98 Second Edition, or Windows Millennium Edition ended on July 11, 2006. I am still using one of these operating systems, what should I do?
Windows 98, Windows 98 Second Edition, or Windows Millennium Edition has reached the end of their support 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.

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:
•

Security level for the Internet zone is set to High. This setting disables scripts, ActiveX controls, Microsoft Java Virtual Machine (MSJVM), and file downloads.
•

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.
•

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.
•

Multimedia content is disabled. This setting prevents music, animations, and video clips from running.

Can I enable trusted HTML Help content outside the Local Machine zone?
Yes. You can enable HTML Help content outside the Local Machine zone. You can allow specific sites or security zones to render HTML Help content. To do this, create either or both of the following registry keys.

Warning When you do this, be very selective and allow only sites or security zones that you trust.

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.

To allow specific sites to render HTML Help content:

Click Start, click Run, type Regedit in the Open box, and then click OK.

Locate and then click the following registry subkey:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\HTMLHelp\1.x
Note If this registry subkey does not exist, create it.

On the Edit menu, point to New, and then click Key.

Type HHRestrictions, and then press ENTER.

Right-click the HHRestrictions subkey, point to New, and then click String Value.

Type UrlAllowList, and then press ENTER.

Right-click the UrlAllowList value and then click Modify.

Add URL prefixes as a semi-colon separated list into the Value Data field, and then press ENTER.
For example, “http://www.wingtiptoys.com/help/helpdocuments;http://myintranetapplication/help/helpfiles” (without the quotation marks).
Note The Value Data field of this registry value is by default blank.

To allow all sites in a specific zone to render HTML Help content:

Click Start, click Run, type Regedit in the Open box, and then click OK.

Locate and then click the following registry subkey:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\HTMLHelp\1.x
Note If this registry subkey does not exist, create it.

On the Edit menu, point to New, and then click Key.

Type HHRestrictions, and then press ENTER.

Right-click the HHRestrictions subkey, point to New, and then click DWORD Value.

Type MaxAllowedZone, and then press ENTER.

Right-click the MaxAllowedZone value and then click Modify.

Change the Value Data field to a number between 0 and 4, and then press ENTER.

Note The Value Data field of this registry value is by default set to 0 (zero). See the following table that outlines how different values are interpreted.
MaxAllowedZone Local Machine zone Local intranet zone Trusted sites zone Internet zone Restricted sites zone

0

Allowed

Blocked

Blocked

Blocked

Blocked

1

Allowed

Allowed

Blocked

Blocked

Blocked

2

Allowed

Allowed

Allowed

Blocked

Blocked

3

Allowed

Allowed

Allowed

Allowed

Blocked

4

Allowed

Allowed

Allowed

Allowed

Allowed

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

Yes

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

Yes

Yes

Microsoft Windows XP Professional x64 Edition

No

Yes

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

Yes

Yes

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

No

Yes

Microsoft Windows Server 2003 x64 Edition family

No

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

Yes

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

Yes

Yes

Microsoft Windows XP Professional x64 Edition

No

Yes

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

Yes

Yes

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

No

Yes

Microsoft Windows Server 2003 x64 Edition family

No

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

Buffer Overrun in HTML Help Vulnerability - CVE-2006-3357

A vulnerability exists in the HTML Help ActiveX control that could allow remote code execution on an affected system. An attacker could exploit the vulnerability by constructing a malicious Web page that could potentially allow remote code execution if a user visited that page. An attacker who successfully exploited this vulnerability could take complete control of an affected system.

Mitigating Factors for Buffer Overrun in HTML Help Vulnerability - CVE-2006-3357:
•

In a Web-based attack scenario, an attacker would have to host a Web site that contains a Web page that is used to exploit this vulnerability (An attacker could also attempt to compromise a Web site to have it serve up a Web page with malicious content to attempt to exploit this vulnerability.). An attacker would have no way to force users to visit a Web site. Instead, an attacker would have to persuade them to visit the Web site, typically by getting them to click a link that takes them to the attacker's site or to a site that has been compromised by the attacker.
•

An attacker who successfully exploited this vulnerability could gain the same privileges as the user. Users whose accounts are configured to have fewer privileges on the system could be less impacted than users who operate with administrative privileges.
•

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. The Restricted sites zone helps reduce attacks that could attempt to exploit this vulnerability.

The risk of attack from the HTML e-mail vector can be significantly reduced if you meet all the following conditions:
•

Install the update that is included with Microsoft Security Bulletin MS03-040 or a later Cumulative Security Update for Internet Explorer.
•

Use Microsoft Outlook 2000 with the Microsoft Outlook E-mail Security Update installed.
•

Use Microsoft Outlook Express 6 or later or Microsoft Outlook 2000 Service Pack 2 or later in their default configuration.
•

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 Buffer Overrun in HTML Help Vulnerability- CVE-2006-3357:

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.
•

Disable the HTML Help ActiveX control from running within Internet Explorer 6 for Windows XP Service Pack 2.

You can help protect against this vulnerability by changing your settings within Internet Explorer to disable the ActiveX control hhtctrl.ocx from running.

To disable the HTML Help ActiveX control in Microsoft Internet Explorer:

On the Internet Explorer Tools menu, click Manage Add-ons.

Locate and click on “HHCTRL Object”.

To disable the add-on, click Disable and then click OK.

Impact of Workaround: Disabling the HTML Help ActiveX control prevents Internet Explorer from instantiating the control. This configuration causes program compatibility issues. Some examples of such issues are:
•

In Help and Support Center, the Index feature no longer works.
•

In HTML Help, features such as Related Topics and Shortcuts no longer work.

Features that are provided by the HTML Help control in Enterprise intranet programs no longer work.
•

Set Internet and Local intranet security zone settings to “High” to prompt before running ActiveX controls and active scripting in the Internet zone and in the Local intranet zone.

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:

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 high security setting.

Alternatively, you can change you settings to prompt before running ActiveX controls only by following 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.

In the Scripting section, under Active Scripting, click Prompt, 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.

In the Scripting section, under Active Scripting, click Prompt.

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 "Restrict Web sites to only your trusted Web sites" workaround.
•

Restrict Web sites to only your trusted Web sites.

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 Internet Explorer's 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.

Add any sites that you trust not to take malicious action on your computer. One in particular that you may want to add is "*.windowsupdate.microsoft.com" (without the quotation marks). This is the site that will host the update, and it requires using an ActiveX control to install the update.
•

Temporarily disable the HTML Help ActiveX control from running in Internet Explorer

You can help protect against this vulnerability by temporarily disabling the HTML Help ActiveX control from running in Internet Explorer by setting the kill bit for the control.

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.

The CLSID for an ActiveX control is a GUID for that control. You can prevent an ActiveX control from running in Internet Explorer by setting the kill bit so that the control is never called by Internet Explorer. The kill bit is a specific value for the Compatibility Flags DWORD value for the ActiveX control in the registry.

The CLSID for the HTML Help ActiveX control is {52a2aaae-085d-4187-97ea-8c30db990436}

For detailed steps about stopping an ActiveX control from running in Internet Explorer, see Microsoft Knowledge Base Article 240797. Follow these steps and create a Compatibility Flags value in the registry to prevent the HTML Help ActiveX control from being instantiated in Internet Explorer

Note If you use this workaround you must reset this registry change by removing the same Compatibility Flags registry value. You should do this after you have applied this security update to regain normal functionality supplied by the HTML Help ActiveX control.

Impact of Workaround: Disabling the HTML Help ActiveX control prevents Internet Explorer from instantiating the control. This configuration causes program compatibility issues. Some examples of such issues are:
•

In Help and Support Center, the Index feature no longer works.
•

In HTML Help, features such as Related Topics and Shortcuts no longer work.

Features that are provided by the HTML Help control in Enterprise intranet programs no longer work.
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FAQ for Buffer Overrun in HTML Help Vulnerability - CVE-2006-3357:

What is the scope of the vulnerability?
This is a vulnerability that could allow remote code execution. If a user is logged on with administrative privileges, an attacker who successfully exploited this vulnerability could take complete control of an affected system. An attacker could then install programs; view, change, or delete data; or create new accounts with full privileges. Users whose accounts are configured to have fewer privileges on the system could be less impacted than users who operate with administrative privileges.

What causes the vulnerability?
A vulnerability in a string buffer, within the HTML Help ActiveX control.

What is HTML Help?
Microsoft HTML Help is the standard help system for the Windows platform. The HTML Help ActiveX control is a program that is used to insert help navigation and secondary window functionality into an HTML file. For more information about the HTML Help ActiveX control, see the product documentation.

What are Internet Explorer security zones?
Internet Explorer security zones are part of a system that divides online content into categories or zones that are based on the trustworthiness of the content. Specific Web domains can be assigned to a zone, depending on how much you trust the content of each domain. The zone then restricts the capabilities of the Web content, based on the zone's policy. By default, most Internet domains are treated as part of the Internet zone. By default, the policy of the Internet zone prevents scripts and other active code from accessing resources on the local system.

What might an attacker use the vulnerability to do?
An attacker who successfully exploited this vulnerability could run malicious code on a users system. This could allow an attacker to take complete control of the affected system.

How could an attacker exploit the vulnerability?
An attacker could exploit this vulnerability by creating a malicious Web page and persuading the user to visit the page. An attacker could also attempt to compromise a Web site to have it serve up a Web page with malicious content to try to exploit this vulnerability. When the user has visited the page, the attacker could access information from other Web sites, access local files on the system, or cause malicious script to run as the locally logged on user.

What systems are primarily at risk from the vulnerability?
This vulnerability requires that a user view Web sites for malicious action to occur. Therefore, any systems where Internet Explorer is used frequently, such as users’ workstations or terminal servers, are at the most risk from this vulnerability. Systems that are not typically used to visit Web sites, such as most server systems, are at a reduced risk.

Could the vulnerability be exploited over the Internet?
An attacker could try to exploit this vulnerability over the Internet. Firewall best practices and standard default firewall configurations can help protect against attacks that originate from the Internet. Microsoft has provided information about how you can help protect your PC. End users can visit the Protect Your PC Web site. IT professionals can visit the Security Guidance Center Web site.

What does the update do?
The update removes the vulnerability by correcting the issue within the affected string buffer.

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 CAN-2006-3357.

When this security bulletin was issued, had Microsoft received any reports that this vulnerability was being exploited?
No. When the security bulletin was released, Microsoft had not received information that this vulnerability was being exploited

Does applying this security update help protect customers from the code that has been published publicly that attempts to exploit this vulnerability?
Yes. This security update addresses the vulnerability. The vulnerability that has been addressed has been assigned the Common Vulnerability and Exposure number CAN-2006-3357.

Acknowledgments

Microsoft thanks to the following for working with us to help protect customers:
•

Cody Pierce of the TippingPoint Security Research Team for working with Microsoft on the Buffer Overrun in HTML Help Vulnerability - CVE-2006-3357.

Disclaimer:

The information provided in the Microsoft Knowledge Base is provided "as is" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.

Revisions:
•

V1.0 (August 8, 2006): Bulletin published.