Microsoft Security Bulletin (MS99-039)

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



Update: Patch Available for "Domain Resolution" and "FTP Download"

Vulnerabilities



Originally Posted: September 23, 1999

Revised: September 30, 1999



Summary

=======

This is a re-release of a security bulletin issued on September 23, 1999.

The purpose of the  re-release is to discuss an additional product,

Microsoft(r) Commercial Internet System, that is  affected by this

vulnerability.  The information regarding IIS has not changed, and customers

who  previously applied this patch to their IIS systems do not need to take

any action.



Microsoft has released a patch that eliminates two security vulnerabilities

in Microsoft Internet Information Server (IIS) 4.0 and Microsoft

Commercial Internet System (MCIS) 2.5. The vulnerabilities allow security

restrictions in IIS and MCIS 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. This vulnerability

   affects IIS 4.0 only; it does not any other Microsoft product,

   including MCIS.

 - 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. This vulnerability affects both IIS 4.0 and MCIS 2.5, but no

   other Microsoft products.



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

 - Microsoft Commercial Internet System 2.5



Patch Availability

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

 - IIS 4.0:

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

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

 - MCIS 2.5:

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

   usa/mcis25/security/ftpsvc-fix/



NOTE: Line breaks have been inserted into the above URLs 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 Knowledge Base (KB) article Q242559,

   FTP Allows read on a file with NTFS permissions of No Access,

   http://support.microsoft.com/support/kb/articles/q242/5/59.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.)



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 Rich Harrison of Halliburton Company for discovering

the "Domain  Resolution" vulnerability and reporting it to us. Microsoft

acknowledges Roberto Franceschetti  for discovering the FTP Access

vulnerability and bringing it to our attention.



Revisions

=========

 - September 23, 1999: Bulletin Created.

 - September 30, 1999: Bulletin modified to include information regarding

   MCIS association with this vulnerability.



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