[NT] Vulnerability in HTML Help ActiveX Control Could Allow Remote Code Execution (MS07-008)

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Vulnerability in HTML Help ActiveX Control Could Allow Remote Code
Execution (MS07-008)
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SUMMARY

A remote code execution vulnerability exists in the HTML Help ActiveX
control. An attacker could exploit the vulnerability by constructing a
specially crafted 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.

DETAILS

Affected Software:
* Microsoft Windows 2000 Service Pack 4 -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=211a9c07-88ff-4ae4-a82a-ce2045c6c4fe> Download the update
* Microsoft Windows XP Service Pack 2 -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=a3700273-d7da-4a60-ba80-c95c8036d670> Download the update
* Microsoft Windows XP Professional x64 Edition -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=69ef4daa-cf0f-4898-8675-911428e7fd74> Download the update
* Microsoft Windows Server 2003 and Microsoft Windows Server 2003 Service
Pack 1 -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=5a1f1607-b6ec-41e2-aac0-34387f1211a7> Download the update
* Microsoft Windows Server 2003 for Itanium-based Systems and Microsoft
Windows Server 2003 with SP1 for Itanium-based Systems -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=d638c8e8-5fbe-4a32-945c-440a4b684b0f> Download the update
* Microsoft Windows Server 2003 x64 Edition -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=65bf2245-6c89-43db-8d28-12988791c395> Download the update

Non-Affected Software:
* Windows Vista

Mitigating Factors for HTML Help ActiveX Control Vulnerability -
CVE-2007-0214:
* By default, all supported versions 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 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.

* 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 have not been added to Internet
Explorer Trusted sites zone.

Workarounds for HTML Help ActiveX Control Vulnerability - CVE-2007-0214:
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.

* Temporarily prevent the HTML Help ActiveX control from running in
Internet Explorer

To protect against this vulnerability, set the kill bit for the ActiveX
control to
temporarily disable the HTML Help ActiveX and keep it from running in
Internet Explorer.
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 the 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.

FAQ for HTML Help ActiveX Control Vulnerability - CVE-2007-0214:
What is the scope of the vulnerability?
This vulnerability 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?
HTML Help ActiveX control methods do not perform sufficient parameter
validation.

What is HTML Help and HTML Help ActiveX control?
Microsoft
<http://msdn.microsoft.com/library/en-us/htmlhelp/html/vsconhh1start.asp>
HTML Help is the standard help system for the Windows platform. HTML Help
ActiveX control is a program (Hhctrl.ocx) that is used to insert help
navigation and secondary window functionality into an HTML file. HTML Help
ActiveX control is designed to work with Internet Explorer and the
Shdocvw.dll component. The Shdocvw.dll exposes interfaces to its host to
allow it to be hosted separately as an ActiveX control. The Shdocvw.dll
component is more frequently referred to as the WebBrowser Control. For
more information about the HTML Help ActiveX control, see the
<http://msdn.microsoft.com/library/en-us/htmlhelp/html/vsconocxov.asp>
product documentation and HTML HELP API support.

What are Internet Explorer security zones?
Internet Explorer <http://support.microsoft.com/kb/174360> 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
arbitrary 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 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 view Web sites for any 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.

I am running Internet Explorer on Windows Server 2003. Does this mitigate
this vulnerability?
Yes. By default, Internet Explorer on Windows Server 2003 runs in a
restricted mode that is known as
<http://msdn.microsoft.com/library/default.asp?url=/workshop/security/szone/overview/esc_changes.asp> Enhanced Security Configuration. This mode sets the security level for the Internet zone to High. This is a mitigating factor for Web sites that have not been added to Internet Explorer Trusted sites zone. See the FAQ section of this security update for more information about Internet Explorer Enhanced Security Configuration.

What is the Internet Explorer Enhanced Security Configuration?
Internet Explorer
<http://msdn.microsoft.com/library/default.asp?url=/workshop/security/szone/overview/esc_changes.asp> 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.

What does the update do?
The update removes the vulnerability by initializing parameters for HTML
Help ActiveX control methods.

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

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.


ADDITIONAL INFORMATION

The information has been provided by Microsoft Security Bulletin MS07-008.
The original article can be found at:
<http://www.microsoft.com/technet/security/bulletin/ms07-008.mspx>
http://www.microsoft.com/technet/security/bulletin/ms07-008.mspx



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