MS02-055: Unchecked Buffer in Windows Help Facility Could Enable Code


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Title: Unchecked Buffer in Windows Help Facility Could

Enable Code Execution (Q323255)

Date: 02 October 2002

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

Impact: Attacker could gain control over user's system

Max Risk: Critical

Bulletin: MS02-055

Microsoft encourages customers to review the Security Bulletin at: http://www.microsoft.com/technet/security/...in/MS02-055.asp

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Issue:

======

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 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.

Risk Rating:

============

- Internet systems: Moderate

- Intranet systems: Moderate

- Client systems: Critical

Patch Availability:

===================

- A patch is available to fix this vulnerability. Please read the

Security Bulletin at

http://www.microsoft.com/technet/security/...in/ms02-055.asp

for information on obtaining this patch.

Acknowledgment:

===============

- David Litchfield of Next Generation Security Software Ltd.

(http://www.nextgenss.com/)and Thor Larholm, Security Researcher,

PivX Solutions, LLC (http://www.pivx.com) for reporting the

Buffer Overrun in HTML Help ActiveX Control.

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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.

Source: Microsoft Email

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This Update, has just appeared on windows update.

www.windowsupdate.com

i presume you should install SP1 First, before installing this update :)

LINKS FIXED FOR ALL YOUR 4 POSTS, YOU ADDED PERIODS TO EACH OF THE END OF THE LINKS, CAUSING ERROR :(

Me Fixed it :)

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