Microsoft Security Bulletin (MS99-058)
--------------------------------------

Patch Available for "Virtual Directory Naming" Vulnerability
Originally Posted: December 21, 1999

Summary
=======
Microsoft has released a patch that eliminates a vulnerability in
Microsoft(r) Internet Information Server and other products that run atop
it. Under certain conditions, the vulnerability could cause a web server to
send the source code of .ASP and other files to a visiting user.

Frequently asked questions regarding this vulnerability can be found at
http://www.microsoft.com/security/bulletins/MS99-058faq.asp.

Issue
=====
If a file on one of the affected web server products resides in a virtual
directory whose name contains a legal file extension, the normal server-side
processing of the file can be bypassed. The vulnerability would manifest
itself in different ways depending on the specific file type requested, the
specific file extension in the virtual directory name, and the permissions
that the requester has in the directory. In most cases, an error would
result and the requested file would not be served. In the worse case, the
source code of .ASP or other files could be sent to the browser.

This vulnerability would be most likely to occur due to administrator error,
or if a product generated an affected virtual directory name by default.
(Front Page Server Extensions is one such product). Recommended security
practices militate against including sensitive information in .ASP and other
files that require server-side processing, and if this recommendation is
observed, there would be no sensitive information divulged even if this
vulnerability occurred. In any event, an affected virtual directory could be
identified during routine testing of the server.

Affected Software Versions
==========================
 - Microsoft Internet Information Server 4.0
 - Microsoft Site Server 3.0
 - Microsoft Site Server Commerce Edition 3.0

Patch Availability
==================
 - Intel:
   http://www.microsoft.com/Downloads/Release.asp?ReleaseID=16378
 - alpha:
   http://www.microsoft.com/Downloads/Release.asp?ReleaseID=16379

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.
 - Microsoft Security Bulletin MS99-058: Frequently Asked Questions,
   http://www.microsoft.com/security/bulletins/MS99-058faq.asp.
 - Microsoft Knowledge Base (KB) article Q238606,
   Page Contents Visible For Certain Virtual Directory Names,
   http://support.microsoft.com/support/kb/articles/q238/6/06.asp.
   (Note: It may take 24 hours from the original posting of this
   bulletin for this KB article to be visible.)
 - Microsoft Knowledge Base (KB) article Q186803,
   Browsing Folders with Script-Mapped Extensions Returns Errors,
   http://support.microsoft.com/support/kb/articles/q186/8/03.asp.
 - 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 Adam Hunger for bringing this issue to our attention.


Revisions
=========
 - December 21, 1999: Bulletin Created.

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