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The U.S. Department of Energy
Computer Incident Advisory Capability
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INFORMATION BULLETIN
MS Heap Overrun in HTR Chunked Encoding Vulnerability
[Microsoft Security Bulletin MS02-028 ]
June 13, 2002 18:00 GMT Number M-089
______________________________________________________________________________
PROBLEM: This vulnerability involves a buffer overrun in the Chunked
Encoding data transfer mechanism in IIS 4.0 and 5.0. It could
be used to overrun heap memory on the system, with the result
of either causing the IIS service to fail or allowing code to
be run on the server.
PLATFORM: Any operating system running:
* Microsoft Internet Information Server 4.0
* Microsoft Internet Information Services 5.0
DAMAGE: The vulnerability could grant varying degrees of control to a
successful attacker, either causing the IIS service to fail or
allowing code to be run on the server.
SOLUTION: Apply available patches.
______________________________________________________________________________
VULNERABILITY The risk is MEDIUM. Depending on the particular version in use,
ASSESSMENT: a server configured using any of the Microsoft security
checklists or security tools would not have the HTR
functionality enabled.
______________________________________________________________________________
LINKS:
CIAC BULLETIN: http://www.ciac.org/ciac/bulletins/m-089.shtml
ORIGINAL BULLETIN:
http://microsoft.com/technet/treeview/default.asp?url=/technet/security/bulletin/MS02-
028.asp
PATCHES:
Microsoft IIS 4.0:
http://www.microsoft.com/Downloads/Release.asp?ReleaseID=39579
Microsoft IIS 5.0:
http://www.microsoft.com/Downloads/Release.asp?ReleaseID=39217
______________________________________________________________________________
[***** Start Microsoft Security Bulletin MS02-028 *****]
Microsoft Security Bulletin MS02-028
Heap Overrun in HTR Chunked Encoding Could Enable Web Server Compromise (Q321599)
Originally posted: June 12, 2002
Summary
Who should read this bulletin: Customers hosting web servers using Microsoft® Windows
NT® 4.0 or Windows® 2000.
Impact of vulnerability: Run code of an attacker's choice on the system
Maximum Severity Rating: Moderate
Recommendation: Customers who have a business-critical reason for retaining HTR
scripting should apply the patch immediately. All others should ensure HTR is
disabled.
Affected Software:
Microsoft Internet Information Server 4.0
Microsoft Internet Information Services 5.0
Technical details
Technical description:
This patch eliminates a newly discovered vulnerability affecting Internet Information
Services. Although Microsoft typically delivers cumulative patches for IIS, in this
case we have delivered a patch that eliminates only this new vulnerability, while
completing a cumulative patch. When the cumulative patch is customer-ready, we will
update this bulletin with information on its availability. The FAQ provides
information on the circumstances surrounding the vulnerability, and why we believe
releasing a singleton patch immediately is in customers' best interests. To ensure
that servers are fully protected against past as well as current vulnerabilities, we
strongly recommend installing the previous cumulative patch (discussed in Microsoft
Security Bulletin MS02-018) before installing this patch.
The vulnerability is similar to the first vulnerability discussed in Microsoft
Security Bulletin MS02-018. Like that vulnerability, this one involves a buffer
overrun in the Chunked Encoding data transfer mechanism in IIS 4.0 and 5.0, and could
likewise be used to overrun heap memory on the system, with the result of either
causing the IIS service to fail or allowing code to be run on the server. The chief
difference between the vulnerabilities is that the newly discovered one lies in the
ISAPI extension that implements HTR – an older, largely obsolete scripting technology
– where the previous one lay in the ISAPI extension that implements ASP.
Mitigating factors:
Microsoft has long recommended disabling HTR functionality unless there is a business-
critical reason for retaining it. Systems on which HTR is disabled would not be at
risk from this vulnerability.
The IIS Lockdown Tool disables HTR by default in all server configurations.
The current version of the URLScan tool provides a means of blocking chunked encoding
transfer requests by default.
On default installations of IIS 5.0, exploiting the vulnerability to run code would
grant the attacker the privileges of the IWAM_computername account, which has only the
privileges commensurate with those of an interactively logged-on unprivileged user.
Severity Rating: Internet Servers Intranet Servers Client Systems
IIS 4.0 Moderate Moderate Moderate
IIS 5.0 Moderate Moderate Moderate
The above assessment is based on the types of systems affected by the vulnerability,
their typical deployment patterns, and the effect that exploiting the vulnerability
would have on them. Although the vulnerability would grant varying degrees of control
to a successful attacker, depending on the particular version in use, a server
configured using any of the Microsoft security checklists or security tools would not
have the HTR functionality enabled.
Vulnerability identifier: CAN-2002-0364
Tested Versions:
Microsoft tested IIS 4.0, 5.0 and 5.1 to assess whether they are affected by these
vulnerabilities. Previous versions are no longer supported, and may or may not be
affected by these vulnerabilities. IIS 6.0 is a beta product, and beta products are
typically not eligible for security patches; however, we have confirmed that no beta
versions of IIS 6.0 are affected by the vulnerability.
Patch availability
Download locations for this patch
Microsoft IIS 4.0:
http://www.microsoft.com/Downloads/Release.asp?ReleaseID=39579
Microsoft IIS 5.0:
http://www.microsoft.com/Downloads/Release.asp?ReleaseID=39217
Additional information about this patch
Installation platforms:
The IIS 4.0 patch can be installed on systems running Windows NT 4.0 Service Pack 6a.
The IIS 5.0 patch can be installed on systems running Windows 2000 Service Pack 1 or
Service Pack 2.
Inclusion in future service packs:
No additional service packs are planned for Windows NT 4.0.
The IIS 5.0 fix will be included in Windows 2000 Service Pack 3.
Reboot needed:
IIS 4.0: A reboot can be avoid by stopping the IIS service, installing the patch with
the /z switch, then restarting the service. Knowledge Base article Q319733 provides
additional information on this procedure.
IIS 5.0: No.
Superseded patches: None.
Verifying patch installation:
IIS 4.0:
To verify that the patch has been installed on the machine, confirm that the following
registry key has been created on the machine:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Hotfix\Q321599.
To verify the individual files, consult the file manifest in Knowledge Base article
Q321599.
IIS 5.0:
To verify that the patch has been installed on the machine, confirm that the following
registry key has been created on the machine:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Updates\Windows 2000\SP3\Q321599.
To verify the individual files, use the date/time and version information provided in
the following registry key:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Updates\Windows 2000\SP3\Q321599\Filelist.
Caveats:
None
Localization:
Localized versions of this patch are available at the locations discussed in "Patch
Availability".
Obtaining other security patches:
Patches for other security issues are available from the following locations:
Security patches are available from the Microsoft Download Center, and can be most
easily found by doing a keyword search for "security_patch".
Patches for consumer platforms are available from the WindowsUpdate web site
All patches available via WindowsUpdate also are available in a redistributable form
from the WindowsUpdate Corporate site.
Other information:
Acknowledgments
Microsoft thanks eEye Digital Security for reporting this issue to us and working with
us to protect customers.
Support:
Microsoft Knowledge Base article Q321599 discusses this issue and will be available
approximately 24 hours after the release of this bulletin. Knowledge Base articles can
be found on the Microsoft Online Support web site.
Technical support is available from Microsoft Product Support Services. There is no
charge for support calls associated with security patches.
Security Resources: The Microsoft TechNet Security Web Site provides additional
information about security in Microsoft products.
Disclaimer:
The information provided in the Microsoft Knowledge Base is provided "as is" without
warranty of any kind. Microsoft disclaims all warranties, either express or implied,
including the warranties of merchantability and fitness for a particular purpose. In
no event shall Microsoft Corporation or its suppliers be liable for any damages
whatsoever including direct, indirect, incidental, consequential, loss of business
profits or special damages, even if Microsoft Corporation or its suppliers have been
advised of the possibility of such damages. Some states do not allow the exclusion or
limitation of liability for consequential or incidental damages so the foregoing
limitation may not apply.
Revisions:
V1.0 (June 12, 2002): Bulletin Created.
[***** End Microsoft Security Bulletin MS02-028 *****]
_______________________________________________________________________________
CIAC wishes to acknowledge the contributions of Microsoft for the
information contained in this bulletin.
_______________________________________________________________________________
CIAC, the Computer Incident Advisory Capability, is the computer
security incident response team for the U.S. Department of Energy
(DOE) and the emergency backup response team for the National
Institutes of Health (NIH). CIAC is located at the Lawrence Livermore
National Laboratory in Livermore, California. CIAC is also a founding
member of FIRST, the Forum of Incident Response and Security Teams, a
global organization established to foster cooperation and coordination
among computer security teams worldwide.
CIAC services are available to DOE, DOE contractors, and the NIH. CIAC
can be contacted at:
Voice: +1 925-422-8193 (7x24)
FAX: +1 925-423-8002
STU-III: +1 925-423-2604
E-mail: ciac@ciac.org
Previous CIAC notices, anti-virus software, and other information are
available from the CIAC Computer Security Archive.
World Wide Web: http://www.ciac.org/
Anonymous FTP: ftp.ciac.org
PLEASE NOTE: Many users outside of the DOE, ESnet, and NIH computing
communities receive CIAC bulletins. If you are not part of these
communities, please contact your agency's response team to report
incidents. Your agency's team will coordinate with CIAC. The Forum of
Incident Response and Security Teams (FIRST) is a world-wide
organization. A list of FIRST member organizations and their
constituencies can be obtained via WWW at http://www.first.org/.
This document was prepared as an account of work sponsored by an
agency of the United States Government. Neither the United States
Government nor the University of California nor any of their
employees, makes any warranty, express or implied, or assumes any
legal liability or responsibility for the accuracy, completeness, or
usefulness of any information, apparatus, product, or process
disclosed, or represents that its use would not infringe privately
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otherwise, does not necessarily constitute or imply its endorsement,
recommendation or favoring by the United States Government or the
University of California. The views and opinions of authors expressed
herein do not necessarily state or reflect those of the United States
Government or the University of California, and shall not be used for
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