Microsoft Security Bulletin (MS99-039)

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



Patch Available for "Domain Resolution" and "FTP Download" Vulnerabilities

Originally Posted: September 23, 1999



Summary

=======

Microsoft has released a patch that eliminates two security

vulnerabilities in Microsoft(r) Internet Information Server 4.0.

The vulnerabilities allow security restrictions in IIS to be

bypassed under certain conditions, as discussed below. Frequently

asked questions regarding this vulnerability can be found at

http://www.microsoft.com/security/bulletins/ms99-039faq.asp.



Issue

=====

There are two vulnerabilities at issue here:

 - IIS 4.0 provides the ability to restrict access to a web

   site based on the user's domain. However, if IIS cannot

   resolve a user's IP address to a domain, it will grant

   the user's first request for a session. It will correctly

   deny them thereafter.

 - A user who accesses an FTP site via a browser will be able

   to download files even if they are marked No Access. This

   vulnerability is due to a regression error that was

   introduced in hotfixes released after Windows NT 4.0 Service

   Pack 5; it does not exist in SP5 or in previous versions.



Neither vulnerability provides a means to usurp control of the server. A

patch is available that  eliminates both vulnerabilities.



Affected Software Versions

==========================

 - Microsoft Internet Information Server 4.0



Patch Availability

==================

 - ftp://ftp.microsoft.com/bussys/iis/iis-public/fixes/

   usa/IIS40/hotfixes-postSP6/security/IPRFTP-fix/



   NOTE: A line break was inserted into the above URL for readability.



More Information

================

Please see the following references for more information related to this

issue.

 - Microsoft Security Bulletin MS99-039: Frequently Asked Questions,

   http://www.microsoft.com/security/bulletins/ms99-039faq.asp.

 - Microsoft Knowledge Base (KB) article Q241805,

   Combined FTP and Domain Restriction Security Patch for IIS 4.0,

   http://support.microsoft.com/support/kb/articles/q241/8/05.asp.

 - Microsoft Knowledge Base (KB) article Q241562,

   Denying Access With Domain Name Restriction Still Allows

   Unresolved Clients,

   http://support.microsoft.com/support/kb/articles/q241/5/62.asp.

 - Microsoft Knowledge Base (KB) article Q241407,

   Files can be downloaded from an FTP Server when the file permissions

   are explicitly No Access,

   http://support.microsoft.com/support/kb/articles/q241/4/07.asp.

 - Microsoft Security Advisor web site,

   http://www.microsoft.com/security/default.asp.



   NOTE: It may take 24 hours from the original posting of this bulletin

   for the KB articles to be visible.



   NOTE: Line breaks have been inserted into the above URLs for readability



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 Roberto Franceschetti for discovering the FTP Access

vulnerability and  bringing it to our attention.



Revisions

=========

 - September 23, 1999: Bulletin Created.



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