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Microsoft Security Bulletin (MS99-039)
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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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