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Vulnerability in HTML Help Allows Code Execution (MS06-046)
------------------------------------------------------------------------
SUMMARY
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.
DETAILS
Affected Software:
* Microsoft Windows 2000 Service Pack 4 -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=34ebe5d3-40c9-41dc-aaff-64608d3ac7b1>
Download the update
* Microsoft Windows XP Service Pack 1 and Microsoft Windows XP Service
Pack 2 -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=a6e2cb0a-146f-4300-95cb-7078ce9f9844>
Download the update
* Microsoft Windows XP Professional x64 Edition -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=997a633a-8836-4c0f-98f9-1fd378de4b0c>
Download the update
* Microsoft Windows Server 2003 and Microsoft Windows Server 2003 Service
Pack 1 -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=5132c3bc-f3af-464e-a615-60f72677bd4b>
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=527cc785-e69e-4ade-aaf7-61f96ac3ca7a>
Download the update
* Microsoft Windows Server 2003 x64 Edition -
<http://www.microsoft.com/downloads/details.aspx?FamilyId=fd1253b0-f4db-4808-a381-98ff9870ebb3>
Download the update
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.
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:
1. On the Internet Explorer Tools menu, click Manage Add-ons.
2. Locate and click on HHCTRL Object .
3. 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:
1. On the Internet Explorer Tools menu, click Internet Options.
2. In the Internet Options dialog box, click the Security tab, and then
click the Internet icon.
3. Under Security level for this zone, move the slider to High. This sets
the security level for all Web sites you visit to High.
Note If no slider is visible, click Default Level, and then move the
slider to High.
Note Setting the level to High may cause some Web sites to work
incorrectly. If you have difficulty using a Web site after you change this
setting, and you are sure the site is safe to use, you can add that site
to your list of trusted sites. This will allow the site to work correctly
even with the high security setting.
Alternatively, you can change you settings to prompt before running
ActiveX controls only by following these steps:
1. In Internet Explorer, click Internet Options on the Tools menu.
2. Click the Security tab.
3. Click Internet, and then click Custom Level.
4. Under Settings, in the ActiveX controls and plug-ins section, under Run
ActiveX controls and plug-ins, click Prompt.
5. In the Scripting section, under Active Scripting, click Prompt, and
then click OK.
6. Click Local intranet, and then click Custom Level.
7. Under Settings, in the ActiveX controls and plug-ins section, under Run
ActiveX controls and plug-ins, click Prompt.
8. In the Scripting section, under Active Scripting, click Prompt.
9. 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:
1. In Internet Explorer, click Tools, click Internet Options, and then
click the Security tab.
2. In the Select a Web content zone to specify its current security
settings box, click Trusted Sites, and then click Sites.
3. If you want to add sites that do not require an encrypted channel,
click to clear the Require server verification (https:) for all sites in
this zone check box.
4. In the Add this Web site to the zone box, type the URL of a site that
you trust, and then click Add.
5. Repeat these steps for each site that you want to add to the zone.
6. Click OK two times to accept the changes and return to Internet
Explorer.
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
<http://support.microsoft.com/kb/240797> 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 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.
ADDITIONAL INFORMATION
The information has been provided by Microsoft Product Security.
The original article can be found at:
<http://www.microsoft.com/technet/security/Bulletin/MS06-046.mspx>
http://www.microsoft.com/technet/security/Bulletin/MS06-046.mspx
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