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Microsoft Security Bulletin (MS99-012)
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MSHTML Update Available for Internet Explorer
Originally Posted: April 21, 1999
Summary
=======
Microsoft has released an updated version of a component of Internet
Explorer 4.0 and 5. The updated version eliminates three security
vulnerabilities described below. It is fully supported and Microsoft
recommends that affected customers download and install it, if appropriate.
Issue
=====
MSHTML.DLL is the parsing engine for HTML in Internet Explorer. The
vulnerabilities that are eliminated by the update are not related to each
other except for the fact that all reside within the parsing engine.
- The first vulnerability is a privacy issue involving
the processing of the "IMG SRC" tag in HTML files. This tag
identifies and loads image sources - image files that are
to be displayed as part of a web page. The vulnerability
results because the tag can be used to point to files of any
type, rather than only image files, after which point the
document object model methods can be used to determine information
about them. A malicious web site operator could use this vulnerability
to determine the size and other information about files on the
computer of a visiting user. It would not allow files to be read or
changed, and the malicious web site operator would need to know the
name of each file.
- The second vulnerability is a new variant of a previously-identified
cross-frame security vulnerability. A particular malformed URL could
be used to execute scripts in the security context of a different
domain. This could allow a malicious web site operator to execute a
script on the web site, and gain privileges on visiting users' machines
that are normally granted only to their trusted sites.
- The third vulnerability affects only Internet Explorer 5.0, and is a
new variant of a previously-identified untrusted scripted paste
vulnerability. The vulnerability would allow a malicious web site
operator to create a particular type of web page control and paste
into it the contents of a visiting user's clipboard.
While there are no reports of customers being adversely affected by any of
these vulnerabilities, Microsoft is proactively releasing an updated version
of MSHTML.DLL to allow customers to take appropriate action to protect
themselves against it.
Affected Software Versions
==========================
- Internet Explorer 4.0 and 5 on Windows 95, Windows 98
and 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 Q226326,
Update Available for MSHTML Security Issues in Internet Explorer,
http://support.microsoft.com/support/kb/articles/q226/3/26.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
http://www.microsoft.com/windows/ie/security/mshtml.asp.
More Information
================
Please see the following references for more information related to this
issue.
- Microsoft Security Bulletin MS99-012,
MSHTML Update Available for Internet Explorer (The Web-posted
version of this bulletin),
http://www.microsoft.com/security/bulletins/ms99-012.asp.
- Microsoft Knowledge Base (KB) article Q226326,
Update Available for MSHTML Security Issues in Internet Explorer,
http://support.microsoft.com/support/kb/articles/q226/3/26.asp.
- Microsoft Security Bulletin MS98-013,
Fix available for Internet Explorer Cross Frame Navigate Vulnerability,
http://www.microsoft.com/security/bulletins/ms98-013.asp
- Microsoft Security Bulletin MS98-015,
Update available for "Untrusted Scripted Paste" Issue in Microsoft
Internet Explorer 4.01,
http://www.microsoft.com/security/bulletins/ms98-015.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 Richard M. Smith, President, Phar Lap Software, Inc.,
for discovering the IMG SRC vulnerability, and Georgi Guninski from
TechnoLogica Ltd., Bulgaria, for discovering the cross-frame and untrusted
scripted paste vulnerabilities.
Revisions
=========
- April 21, 1999: Bulletin Created.
For additional security-related information about Microsoft products, please
visit http://www.microsoft.com/security
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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,
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LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE
FOREGOING LIMITATION MAY NOT APPLY.
(c) 1999 Microsoft Corporation. All rights reserved.
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