[12766] in bugtraq
Microsoft Security Bulletin (MS99-051) (fwd)
daemon@ATHENA.MIT.EDU (Ben Greenbaum)
Mon Nov 29 21:23:05 1999
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Message-Id: <Pine.GSO.4.10.9911291742150.19134-100000@www.securityfocus.com>
Date: Mon, 29 Nov 1999 17:42:36 -0800
Reply-To: Ben Greenbaum <bgreenbaum@SECURITYFOCUS.COM>
From: Ben Greenbaum <bgreenbaum@SECURITYFOCUS.COM>
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To: BUGTRAQ@SECURITYFOCUS.COM
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Date: Mon, 29 Nov 1999 17:18:19 -0800
From: Microsoft Product Security <secnotif@MICROSOFT.COM>
To: MICROSOFT_SECURITY@ANNOUNCE.MICROSOFT.COM
Subject: Microsoft Security Bulletin (MS99-051)
The following is a Security Bulletin from the Microsoft Product Security
Notification Service.
Please do not reply to this message, as it was sent from an unattended
mailbox.
********************************
Microsoft Security Bulletin (MS99-051)
--------------------------------------
Patch Available for "IE Task Scheduler" Vulnerability
Originally Posted: November 29, 1999
Summary
=======
Microsoft has released a version upgrade that eliminates a vulnerability in
Microsoft(r) Internet Explorer 5. A vulnerability in an optional component
could allow a malicious user to gain additional privileges on a Windows NT
machine that allowed him or her to create or change files.
Frequently asked questions regarding this vulnerability can be found at
http://www.microsoft.com/security/bulletins/MS99-051faq.asp.
Issue
=====
IE 5 includes an Offline Browsing Pack that is not installed by default. The
Offline Browsing Pack provides a Task Scheduler that replaces the native
Windows NT Schedule Service (the schedule service is also known as the "AT
Service"). A vulnerability in the Task Scheduler poses a privilege elevation
risk and could allow normal users to execute code on the local machine in
System context. (The Windows NT Schedule Service does not have this
vulnerability).
The IE 5 Task Scheduler controls who can create and submit "AT jobs." The
utility that is used to create AT jobs can only be run by an administrator,
and the Task Scheduler will only execute AT jobs that are owned by
administrators. However, if a malicious user had change access to an
existing file owned by an administrator (it would not need to be an AT job),
he or she could modify it to be a valid AT job and place in the appropriate
folder for execution. This would bypass the control mechanism and allow the
job to be executed.
This vulnerability would primarily affect machines that allow normal users
to interactively log onto them. The patch eliminates this vulnerability by
digitally signing all AT jobs at creation time, and verifying the signature
at execution time.
Affected Software Versions
==========================
- Microsoft Internet Explorer 5, when run on a Windows NT 4.0 system
NOTE: The affected components are part of the IE 5 Offline Browsing Pack,
which is not installed by default.
NOTE: Windows NT 4.0 includes a native scheduling service, but it does not
have this vulnerability.
Patch Availability
==================
The vulnerability is eliminated by IE 5.01, which is available at:
- http://www.microsoft.com/msdownload/iebuild/ie501_win32/
en/ie501_win32.htm
NOTE: A line break has been inserted into the above URL for readability.
More Information
================
Please see the following references for more information related to this
issue.
- Microsoft Security Bulletin MS99-051: Frequently Asked Questions,
http://www.microsoft.com/security/bulletins/MS99-051faq.asp.
- Microsoft Knowledge Base (KB) article Q246972,
IE 5 Task Scheduler Allows Privilege Elevation on Windows NT Systems,
http://support.microsoft.com/support/kb/articles/q245/7/29.asp.
(NOTE: It may take 24 hours from the original posting of this bulletin
for this KB article to be visible)
- Microsoft Security Advisor web site,
http://www.microsoft.com/security/default.asp.
Obtaining Support on this Issue
===============================
This is a fully supported patch. Information on contacting Microsoft
Technical Support is available at
http://support.microsoft.com/support/contact/default.asp.
Acknowledgments
===============
Microsoft acknowledges Arne Vidstrom and Svante Sennmark for bringing this
issue to our attention.
Revisions
=========
- November 29, 1999: Bulletin Created
----------------------------------------------------------------------
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