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Microsoft Security Bulletin (MS99-015)
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Patch Available for "Malformed Help File" Vulnerability
Originally Posted: May 17, 1999
Summary
=======
Microsoft has released a patch that eliminates a vulnerability in the
Microsoft (r) Windows NT (r) help utility. The vulnerability could allow
arbitrary code to be run on a Windows NT machine.
A fully supported patch is available to eliminate the vulnerability, and
Microsoft recommends that affected customers download and install it, if
appropriate.
Issue
=====
The Windows Help utility parses and displays help information for
applications. The help information is contained in files of several types
that are generated by the Help Compiler (part of the AppWizard utility), and
is stored by default in the WINNT\help folder. By default, users can write
to this folder. An unchecked buffer exists in the Help utility, and a help
file that has been carefully modified could be used to execute arbitrary
code on the local machine via a classic buffer overrun technique. Because
the Help Compiler's output files do not generate the specific malformation
at issue here, this vulnerability could not be accidentally exploited.
The machines primarily at risk from this vulnerability are workstations,
terminal servers, and other machines that allow users to log on
interactively and add or modify help files. Servers generally do not allow
normal users to interactively log on. It is important to note that this
vulnerability would affect only the local machine; there is no capability to
directly attack a remote machine via this vulnerability.
The patch prevents arbitrary code from being executed on the machine, but
does not prevent malformed help files from causing the Help utility to fail.
However, failure of the Help utility does not threaten system stability or
security, and the Help utility can be restarted without incident.
While there are no reports of customers being adversely affected by this
vulnerability, Microsoft is proactively releasing this patch to allow
customers to take appropriate action to protect themselves against it.
Affected Software Versions
==========================
- Microsoft Windows NT 4.0
What Microsoft is Doing
=======================
Microsoft has released patches that fix the problem identified. The patches
are available for download from the sites listed below in What Customers
Should Do.
Microsoft also has sent this security bulletin to customers
subscribing to the Microsoft Product Security Notification Service.
See http://www.microsoft.com/security/services/bulletin.asp for
more information about this free customer service.
Microsoft has published the following Knowledge Base (KB) article on this
issue:
- Microsoft Knowledge Base (KB) article Q231605,
Malformed Help File Causes Help Utility to Stop Responding,
http://support.microsoft.com/support/kb/articles/q231/6/05.asp
(Note: It might take 24 hours from the original posting of this
bulletin for the KB article to be visible in the Web-based
Knowledge Base.)
What Customers Should Do
========================
Microsoft highly recommends that customers evaluate the degree of risk that
this vulnerability poses to their systems and determine whether to download
and install the patch. The patch can be found at:
- X86 version:
ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/usa/nt40
/hotfixes-po stSP5/winhlp32-fix/winhlp-i.exe
- Alpha version:
ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/usa/nt40
/hotfixes-po stSP5/winhlp32-fix/winhlp-a.exe
NOTE: The above URLs have been word-wrapped for readability
More Information
================
Please see the following references for more information related to this
issue.
- Microsoft Security Bulletin MS99-015,
Patch Available for 'Malformed Help File' Vulnerability
(The Web-posted version of this bulletin),
http://www.microsoft.com/security/bulletins/ms99-015.asp.
- Microsoft Knowledge Base (KB) article Q231605,
Malformed Help File Causes Help Utility to Stop Responding,
http://support.microsoft.com/support/kb/articles/q231/6/05.asp
Obtaining Support on this Issue
===============================
If you require technical assistance with this issue, please contact
Microsoft Technical Support. For information on contacting Microsoft
Technical Support, please see
http://support.microsoft.com/support/contact/default.asp.
Acknowledgments
===============
Microsoft acknowledges David Litchfield (mnemonixat_private) of Arca
Systems for discovering this vulnerability and reporting it to us.
Revisions
=========
- May 17, 1999: Bulletin Created.
For additional security-related information about Microsoft products,
please visit http://www.microsoft.com/security
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