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Microsoft Security Bulletin (MS99-003)
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Patch Available for IIS "Malformed FTP List Request" Vulnerability
Originally Posted: February 3, 1999
Summary
=======
Microsoft has released a patch that eliminates a vulnerability in the
Internet Information Server (r) FTP service. This vulnerability could allow
denial of service attacks against the server or, under certain conditions,
could allow arbitrary code to be executed on the server.
A fully supported fix for this problem is available. As detailed below in
What Customers Should Do, Microsoft recommends that customers who are at
risk from this vulnerability apply the patch.
Issue
=====
The FTP service in IIS has an unchecked buffer in a component that processes
"list" commands. This results in a vulnerability that poses two threats to
safe operation. The first is a denial of service threat; a malformed "list"
request could overflow the buffer causing the server to crash. The second is
more esoteric and would be far more difficult to exploit. A
carefully-constructed "list" request could cause arbitrary code to execute
on the server via a classic buffer overrun technique. Neither variant could
be exploited accidentally.
It is noteworthy that the "list" command is only available to users after
they have authenticated to the server. As a result, only users who are
authorized to use the server would be able to mount such an attack, and
their presence on the server could be logged if the owner of the site chose
to do so. However, many sites provide guest accounts, and this could allow a
malicious user to attack the server anonymously.
Microsoft has no reports of any customers being affected by this
vulnerability. However, Microsoft is proactively releasing a patch that
corrects the problem.
Affected Software Versions
==========================
The following software versions are affected:
- Microsoft Internet Information Server 3.0 and 4.0
What Microsoft is Doing
=======================
On February 3rd, Microsoft released a patch that fixes the problem
identified above. This patch is available for download from the sites listed
below.
Microsoft has sent this security bulletin to customers subscribing
to the Microsoft Product Security Notification Service (see
http://www.microsoft.com/security/services/bulletin.asp for
more information about this free customer service).
Microsoft has published the following Knowledge Base (KB) article on this
issue:
- Microsoft Knowledge Base (KB) article Q188348,
Specially-Malformed FTP Requests Can Create Denial of Service
http://support.microsoft.com/support/kb/articles/q188/3/48.asp
(Note: It might take 24 hours from the original posting of this
bulletin for the KB article to be visible in the Web-based
Knowledge Base.)
Microsoft has posted hot fixes to address this problem. Please note that all
of these patches are designed to be applied atop Windows NT (r) 4.0 SP4.
The URLs below have been word-wrapped for readability.
- Fix for X86 version of IIS 3.0:
ftp://ftp.microsoft.com/bussys/iis/iis-public/
fixes/usa/security/ftpls-fix/ftpls3i.exe
- Fix for Alpha version of IIS 3.0:
ftp://ftp.microsoft.com/bussys/iis/iis-public/
fixes/usa/security/ftpls-fix/ftpls3a.exe
- Fix for X86 version of IIS 4.0:
ftp://ftp.microsoft.com/bussys/iis/iis-public/
fixes/usa/security/ftpls-fix/ftpls4i.exe
- Fix for Alpha version of IIS 4.0:
ftp://ftp.microsoft.com/bussys/iis/iis-public/
fixes/usa/security/ftpls-fix/ftpls4a.exe
What customers should do
========================
Microsoft highly recommends that all affected customers download the patch
to protect their computers. The complete URL for each affected software
version is provided above in What Microsoft is Doing.
More Information
================
Please see the following references for more information related to this
issue.
- Microsoft Security Bulletin MS99-003,
Patch Available for IIS "Malformed FTP List Request"
Vulnerability (the Web-posted version of this bulletin),
http://www.microsoft.com/security/bulletins/ms99-003.asp.
- Microsoft Knowledge Base (KB) article Q188348,
Specially-Malformed FTP Requests Can Create Denial of Service,
http://support.microsoft.com/support/kb/articles/q188/3/48.asp
(Note: It might take 24 hours from the original posting of this
bulletin for the KB article to be visible in the Web-based
Knowledge Base.)
Acknowledgements
================
Microsoft wishes to acknowledge the eEye Digital Security Team for
discovering this vulnerability.
Obtaining Support on this Issue
===============================
This is a supported patch. If you have problems installing this
patch or require technical assistance with this patch, please
contact Microsoft Technical Support. For information on
contacting Microsoft Technical Support, please see
http://support.microsoft.com/support/contact/default.asp.
Revisions
=========
- February 3, 1999: Bulletin Created
For additional security-related information about Microsoft products,
please visit http://www.microsoft.com/security
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