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Microsoft Security Bulletin (MS00-078)
- --------------------------------------

Patch Available for "Web Server Folder Traversal" Vulnerability

Originally posted: October 17, 2000

Summary
=======
Microsoft has released a patch that eliminates a security
vulnerability in Microsoft(r) IIS 4.0 and 5.0. The vulnerability
could potentially allow a visitor to a web site to take a wide range
of destructive actions against it, including running  programs on it.

This vulnerability is eliminated by the patch that accompanied
Microsoft Security Bulletin MS00-057. Customers who have  applied
that patch are already protected against the vulnerability and do not
need to take additional action. Microsoft  strongly urges all
customers using IIS 4.0 and 5.0 who have not already done so to apply
the patch immediately.

Frequently asked questions regarding this vulnerability
and the patch can be found at
http://www.microsoft.com/technet/security/bulletin/fq00-078.asp

Issue
=====
Due to a canonicalization error in IIS 4.0 and 5.0, a particular type
of malformed URL could be used to access files and  folders that lie
anywhere on the logical drive that contains the web folders. This
would potentially enable a malicious user  who visited the web site
to gain additional privileges on the machine - specifically, it could
be used to gain privileges  commensurate with those of a locally
logged-on user. Gaining these permissions would enable the malicious
user to add, change  or delete data, run code already on the server,
or upload new code to the server and run it.

The request would be processed under the security context of the
IUSR_machinename account, which is the anonymous user  account for
IIS. Within the web folders, this account has only privileges that
are appropriate for untrusted users. However,  it is a member of the
Everyone and Users groups and, as a result, the ability of the
malicious user to access files outside  the web folders becomes
particularly significant. By default, these groups have execute
permissions to most operating system  commands, and this would give
the malicious user the ability to cause widespread damage. Customers
who have proactively  removed the Everyone and Users groups from
permissions on the server, or who are hosting the web folders on a
different drive  from the operating system, would be at significantly
less risk from the vulnerability.

Microsoft strongly recommends that all customers running IIS 4.0 or
5.0 immediately apply the patch for this vulnerability.  This patch
was originally released in August 2000 as a fix for a completely
different vulnerability (discussed in Microsoft  Security Bulletin
MS00-057), and customers who have already applied it do not need to
take any additional action.

Affected Software Versions
==========================
 - Microsoft IIS 4.0
 - Microsoft IIS 5.0

Patch Availability
==================
 - Microsoft IIS 4.0:
   http://www.microsoft.com/ntserver/nts/downloads/critical/q269862
 - Microsoft IIS 5.0:
   http://www.microsoft.com/windows2000/downloads/critical/q269862

Note: The IIS 4.0 patch can be installed on systems running Windows
NT(r) 4.0 Service Packs 5 and 6a. It will be included in  Windows NT
4.0 Service Pack 7. The IIS 5.0 patch can be installed on systems
running either Windows(r) 2000 Gold or Service  Pack 1. It will be
included in Windows 2000 Service Pack 2.

Note: The Download Center pages discussed above may, for the next
several days, only reference the "File Permissions  Canonicalization"
vulnerability. However, we are updating the pages to state that it
applies to both that vulnerability and  this one.

Note: Additional security patches are available at the Microsoft
Download Center

More Information
================
Please see the following references for more information related to
this issue.
 - Frequently Asked Questions: Microsoft Security Bulletin MS00-078,
   http://www.microsoft.com/technet/security/bulletin/fq00-078.asp
 - Microsoft Security Bulletin MS00-057, Microsoft Security Bulletin
   http://www.microsoft.com/technet/security/bulletin/ms00-057.asp
 - Microsoft Knowledge Base article Q276489 discusses this issue and
   will be available soon.
 - Microsoft TechNet Security web site,
   http://www.microsoft.com/technet/security/default.asp

Obtaining Support on this Issue
===============================
This is a fully supported patch. Information on contacting Microsoft
Product Support Services is available at
http://support.microsoft.com/support/contact/default.asp.

Acknowledgments
===============
Microsoft thanks Rain Forest Puppy for reporting this issue to us and
working with us to protect customers.

Revisions
=========
 - October 17, 2000: Bulletin Created.

- ------------------------------------------------------

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WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF
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SO THE FOREGOING LIMITATION MAY NOT APPLY.

Last Updated October 17, 2000

(c) 2000 Microsoft Corporation. All rights reserved. Terms of use.


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