__________________________________________________________
The U.S. Department of Energy
Computer Incident Advisory Capability
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INFORMATION BULLETIN
Microsoft HTML Help ActiveX Control Vulnerabilities
[Microsoft Security Bulletin MS02-055]
October 3, 2002 18:00 GMT Number N-002
______________________________________________________________________________
PROBLEM: An unchecked buffer vulnerability exists in the ActiveX control
that provides the functionality for the HTML Help facility.
Also found were two flaws allowing restrictions to be bypassed
that handle the compiled HTML Help Files containing shortcuts
enabling these files to take any desired system function.
PLATFORM: Microsoft Windows 98
Microsoft Windows 98-Second Edition
Microsoft Windows Millennium Edition
Microsoft Windows NT 4.0
Microsoft Windows NT 4.0, Terminal Server Edition
Microsoft Windows 2000
Microsoft Windows XP
DAMAGE: At worst, an attacker could gain the same privileges as a user
and run code of his/her choice at that privilege level.
SOLUTION: Apply available patch.
______________________________________________________________________________
VULNERABILITY The risk is LOW. A user would need to visit a web page hosted
ASSESSMENT: by the attacker that contains the malicious file, or the
attacker would need to send the user an HTML e-mail that
delivers a .chm file containing a shortcut which makes use of
the flaws.
______________________________________________________________________________
LINKS:
CIAC BULLETIN: http://www.ciac.org/ciac/bulletins/n-002.shtml
ORIGINAL BULLETIN:
http://www.microsoft.com/technet/treeview/default.asp?url=
/technet/security/bulletin/MS02-055.asp
PATCHES: - Windows 98 and Windows 98 SE:
http://www.microsoft.com/windows98/downloads/contents/
WUCritical/q323255/default.asp
- Windows Me:
Only available via http://windowsupdate.microsoft.com/
- Windows NT 4.0:
http://www.microsoft.com/Downloads/Release.asp?ReleaseID=43308
- Windows NT 4.0, Terminal Server Edition:
http://www.microsoft.com/Downloads/Release.asp?ReleaseID=43308
- Windows 2000:
http://www.microsoft.com/Downloads/Release.asp?ReleaseID=40213
- Windows XP Home Edition and Professional Edition:
http://www.microsoft.com/Downloads/Release.asp?ReleaseID=41834
______________________________________________________________________________
[***** Start Microsoft Security Bulletin MS02-055 *****]
Microsoft Security Bulletin MS02-055
Unchecked Buffer in Windows Help Facility Could Enable Code Execution (Q323255)
Originally posted: October 02, 2002
Summary
Who should read this bulletin: Customers using Microsoft® Windows® 98, Windows Me,
Windows NT® 4.0, Windows 2000, or Windows XP.
Impact of vulnerability: Attacker could gain control over user’s system.
Maximum Severity Rating: Critical
Recommendation: Customers should install the patch immediately.
Affected Software:
Microsoft Windows 98
Microsoft Windows 98 Second Edition
Microsoft Windows Millennium Edition
Microsoft Windows NT 4.0
Microsoft Windows NT 4.0, Terminal Server Edition
Microsoft Windows 2000
Microsoft Windows XP
Technical details
Technical description:
The HTML Help facility in Windows includes an ActiveX control that provides
much of its functionality. One of the functions exposed via the control
contains an unchecked buffer, which could be exploited by a web page hosted
on an attacker’s site or sent to a user as an HTML mail. An attacker who
successfully exploited the vulnerability would be able to run code in the
security context of the user, thereby gaining the same privileges as the
user on the system.
A second vulnerability exists because of flaws associated with the handling of
compiled HTML Help (.chm) files that contain shortcuts. Because shortcuts allow
HTML Help files to take any desired action on the system, only trusted HTML Help
files should be allowed to use them. Two flaws allow this restriction to be
bypassed. First, the HTML Help facility incorrectly determines the Security
Zone in the case where a web page or HTML mail delivers a .chm file to the
Temporary Internet Files folder and subsequently opens it. Instead of handling
the .chm file in the correct zone – the one associated with the web page or
HTML mail that delivered it – the HTML Help facility incorrectly handles it
in the Local Computer Zone, thereby considering it trusted and allowing it
to use shortcuts. This error is compounded by the fact that the HTML Help
facility doesn’t consider what folder the content resides in. Were it to do so,
it could recover from the first flaw, as content within the Temporary Internet
Folder is clearly not trusted, regardless of the Security Zone it renders in.
The attack scenario for this vulnerability would be complex, and involves using
an HTML mail to deliver a .chm file that contains a shortcut, then making use
of the flaws to open it and allow the shortcut to execute. The shortcut would
be able to perform any action the user had privileges to perform on the system.
Before deploying the patch, customers should familiarize themselves with the
caveats discussed in the FAQ and in the Caveats section below.
Mitigating factors:
Buffer Overrun in HTML Help ActiveX Control:
The HTML mail-based attack vector could not be exploited on systems where
Outlook 98 or Outlook 2000 were used in conjunction with the Outlook Email
Security Update, or Outlook Express 6 or Outlook 2002 were used in their
default configurations.
The vulnerability would convey only the user’s privileges on the system. Users
whose accounts are configured to have few privileges on the system would be at less
risk than ones who operate with administrative privileges.
Code Execution via Compiled HTML Help File:
The vulnerability could not be exploited via a web site.
The vulnerability could only be exploited if the attacker were able to determine
the exact location of the Temporary Internet Files folder. By design, this
should not be possible, and Microsoft is unaware of any means for doing so
which has not already been patched.
The vulnerability would convey only the user’s privileges on the system. Users
whose accounts are configured to have few privileges on the system would be at
less risk than ones who operate with administrative privileges.
Severity Rating:
Buffer Overrun in HTML Help ActiveX Control:
Internet Servers Intranet Servers Client Systems
All affected products Moderate Moderate Critical
Code Execution via Compiled HTML Help File:
Internet Servers Intranet Servers Client Systems
All affected products Low Low Moderate
The above assessment is based on the types of systems affected by the
vulnerability, their typical deployment patterns, and the effect that
exploiting the vulnerability would have on them.
Vulnerability identifier:
Buffer Overrun in HTML Help ActiveX Control: CAN-2002-0693
Code Execution via Compiled HTML Help File: CAN-2002-0694
Tested Versions:
Microsoft tested the HTML Help facilities in Windows 98, Windows 98 SE,
Windows ME, Windows NT 4.0, Windows 2000 and Windows XP to assess whether
they are affected by these vulnerabilities. Previous versions are no longer
supported, and may or may not be affected by these vulnerabilities.
Patch availability
Download locations for this patch
The patches for all Windows systems are available via Windows Update or can
be manually applied via the following patches:
Windows 98 and Windows 98 SE:
http://www.microsoft.com/windows98/downloads/contents/WUCritical/q323255/
default.asp
Windows Me:
Only available via Windows Update.
Windows NT 4.0:
http://www.microsoft.com/Downloads/Release.asp?ReleaseID=43308
Windows NT 4.0, Terminal Server Edition:
http://www.microsoft.com/Downloads/Release.asp?ReleaseID=43308
Windows 2000:
http://www.microsoft.com/Downloads/Release.asp?ReleaseID=40213
Windows XP Home Edition and Professional Edition:
http://www.microsoft.com/Downloads/Release.asp?ReleaseID=41834
Additional information about this patch
Installation platforms:
The Window 98 patch can be installed on systems running Windows 98 Gold.
The Window 98SE patch can be installed on systems running Windows 98SE Gold.
The Windows Me patch can be installed on systems running Windows Me Gold.
The Windows NT 4.0 patch can be installed on systems running Service Pack 6a.
The Windows NT 4.0 Terminal Server Edition patch can be installed on systems
running Windows NT 4.0 Terminal Server Edition Service Pack 6.
The Windows 2000 patch can be installed on systems running Windows 2000 Service
Pack 1, Service Pack 2 or Service Pack 3.
The patch for Windows XP can be installed on systems running Windows XP Gold or
Service Pack 1.
Inclusion in future service packs:
The fix for this issue will be included in Windows 2000 Service Pack 4 and
Windows XP Service Pack 2.
Reboot needed: Yes
Patch can be uninstalled: No
Superseded patches:
This patch supersedes the one delivered in Microsoft Security Bulletin MS00-037.
Verifying patch installation:
Windows 98, Windows 98SE and Window Me:
To verify that the patch has been installed on the machine, use the
Qfecheck.exe tool and confirm that the display includes the following information:
UPD323255 Windows xx Q323255 Update
where xx is “98” for Windows 98 or 98SE, or “Me” for Windows Me.
To verify the individual files, consult the file manifest in Knowledge Base
article Q323255.
Windows NT 4.0:
To verify that the patch has been installed on the machine, confirm that all
files listed in the file manifest in Knowledge Base article Q323255 are present
on the system.
Windows NT 4.0 Terminal Server Edition:
To verify that the patch has been installed on the machine, confirm that all
files listed in the file manifest in Knowledge Base article Q323255 are present
on the system.
Windows 2000:
To verify that the patch has been installed on the machine, confirm that the
following registry key has been created on the machine:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Updates\Windows 2000\SP4\Q323255.
To verify the individual files, use the date/time and version information
provided in the following registry key:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Updates\Windows 2000\SP4\Q323255\Filelist.
Windows XP:
To verify that the patch has been installed, confirm that the following registry
key has been created on the machine:
HKLM\Software\Microsoft\Updates\Windows XP\SP2\Q323255.
To verify the individual files, use the date/time and version information provided
in the following registry key:
HKLM\Software\Microsoft\Updates\Windows XP\SP2\Q323255\Filelist.
Caveats:
The patch requires that Internet Explorer 5.01, 5.5 or 6 be installed on the
system.
As discussed in the FAQ, the patch does not set the Kill Bit on the affected
control.
Localization:
Localized versions of this patch are available at the locations discussed in
“Patch Availability”. In particular, please note that the patch for Windows NT
4.0 and Windows NT 4.0 Terminal Server Edition can be installed on any language
version, where there is a separately localized patch for other platforms.
Obtaining other security patches:
Patches for other security issues are available from the following locations:
Security patches are available from the Microsoft Download Center, and can be most
easily found by doing a keyword search for "security_patch".
Patches for consumer platforms are available from the WindowsUpdate web site
Other information:
Acknowledgments
Microsoft thanks David Litchfield of Next Generation Security Software Ltd.
and Thor Larholm, Security Researcher, PivX Solutions, LLC (http://www.pivx.com)
for reporting the Buffer Overrun in HTML Help ActiveX Control to us and working
with us to protect customers.
Support:
Microsoft Knowledge Base article Q323255 discusses this issue and will be available
approximately 24 hours after the release of this bulletin. Knowledge Base articles
can be found on the Microsoft Online Support web site.
Technical support is available from Microsoft Product Support Services. There is
no charge for support calls associated with security patches.
Security Resources: The Microsoft TechNet Security Web Site provides additional
information about security in Microsoft products.
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 (October 02, 2002): Bulletin Created.
[***** End Microsoft Security Bulletin MS02-055 *****]
_______________________________________________________________________________
CIAC wishes to acknowledge the contributions of Microsoft Corporation for the
information contained in this bulletin.
_______________________________________________________________________________
CIAC, the Computer Incident Advisory Capability, is the computer
security incident response team for the U.S. Department of Energy
(DOE) and the emergency backup response team for the National
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