Security Bulletin (MS00-044)

2000-07-1500:00:00

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Microsoft Security Bulletin (MS00-044)

Patch Available for "Absent Directory Browser Argument" Vulnerability

Originally Posted: July 14, 2000

Summary

Microsoft has released a patch that eliminates two security
vulnerabilities in Microsoft(r) Internet Information Server. In sum,
the vulnerabilities could allow a malicious user to stop the web
server from providing useful service, or to extract certain types of
information from it.

Frequently asked questions regarding this vulnerability and the patch
can be found at
http://www.microsoft.com/technet/security/bulletin/fq00-044.asp

Issue

There are two vulnerabilities at issue here:

The "Absent Directory Browser Argument" vulnerability. An
administrative script installed as part of IIS 3.0 but preserved
on upgrade to IIS 4.0 or IIS 5.0 does not correctly handle the
case where an expected argument is missing. The absence of the
argument causes the script to go into an infinite loop, at which
point the script consumes all CPU resources on the server. In
addition, the permissions on this tool and several related ones,
which were appropriate under IIS 3.0, are inappropriate under
IIS 4.0 and 5.0. This could allow web site visitors to use these
tools, which provide the ability to view the directory structure
on the server.
A new variant on the "File Fragment Reading via .HTR"
vulnerability. The original version of this vulnerability was
discussed in Microsoft Security Bulletin MS00-031. The new
vulnerability differs only in the specific way that it could be
exploited - like the original version, the effect of the
vulnerability is that fragments of .ASP and other files could
potentially be retrieved from the server. As in the original
version, the mechanics of the new variant make it likely that
the parts of an .ASP file most interesting to a malicious user
would be stripped out.

Microsoft believes that the most appropriate way to eliminate these
vulnerabilities is to remove the script mapping for HTR, as
discussed in the IIS 4.0 Security Checklist. Only customers with
business-critical HTR scripts should retain the functionality and
install the patch.

Affected Software Versions

Microsoft Internet Information Server 4.0
Microsoft Internet Information Server 5.0

Patch Availability

Note: The patch should only be installed by customers who have a
business-critical need for the .HTR functionality. Microsoft
recommends that all other customers disable the .HTR functionality
altogether, as discussed in the FAQ.

Note: Customers who choose to install the patch should also
strengthen the permissions on the /scripts/iisadmin folder in each
web site on the server, and ensure that only administrators can
access it.

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 MS00-044,
http://www.microsoft.com/technet/security/bulletin/fq00-044.asp
Microsoft Knowledge Base article Q267559 discusses the "Absent
Directory Browser Argument" and will be available soon.
Microsoft Knowledge Base article Q267560 discusses the new
variant of the "File Fragment Reading via .HTR" 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 the following customers for working with us to
protect customers:

Peter Grundl for reporting the "Absent Directory Browser Argument"
issue to us
Zuo Lei for reporting the new variant of the "File Fragment
Reading via .HTR" vulnerability to us.

Revisions

July 14, 2000: Bulletin Created.

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SO THE FOREGOING LIMITATION MAY NOT APPLY.

Last Updated July 14, 2000