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[ For Public Release ]
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The U.S. Department of Energy
Computer Incident Advisory Capability
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INFORMATION BULLETIN
Microsoft IIS Boundary Condition Vulnerability
June 26, 1997 20:00 GMT Number H-77
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PROBLEM: A vulnerability in Microsoft Internet Information Server (IIS)
allows an outside user to cause an access violation on a server
("denial of service").
PLATFORM: Windows NT servers running Internet Information Server 2.0
or 3.0.
DAMAGE: Causes an access violation (i.e., server is unresponsive).
Unsaved data is lost.
SOLUTION: Apply the local Microsoft patch described below.
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VULNERABILITY Exploit is widely available, and attack can be successfully
ASSESSMENT: executed remotely.
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Introduction:
A vulnerability in Microsoft Internet Information Server (IIS) for Windows NT
4.0 allows users to locally or remotely cause an access violation on a Web
server of this configuration. The result is the server crashes, and is
therefore rendered unresponsive until rebooted. To determine whether your IIS
server has been successfully attacked, this access violation may be seen in
Event Viewer's Application log file as a Dr. Watson entry of access violation
on the INETINFO.EXE process.
Problem:
A Web browser sends a request such as a URL to the IIS Web server. If the
request is a certain length, the sender causes an access violation on the
server. This length varies from server to server, but typically ranges between
4K and 8K. Code is available which sends requests of varying sizes (lengths)
to the target IIS server. Through this "trial and error", the code will
eventually send the exact size request needed to render the target server
unresponsive.
Solution:
If your server has been successfully attacked, it must be rebooted. The
system operates normally once the system is rebooted.
Prevention:
Microsoft has developed a local patch to prevent users from successfully
accomplishing this attack. This patch detects when the specific URL length
is reached in IIS. CIAC recommends that you update your Emergency Repair Disk
before you apply the patch, as the patch has not been regression tested and
therefore may not work as described.
Microsoft's patch location:
Windows NT 4.0 (CIAC recommends that Service Pack 3 is installed first):
ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/usa/nt40/hotfixes-
postSP3/iis-fix/
===========================================================================
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: +1 510-422-8193
FAX: +1 510-423-8002
STU-III: +1 510-423-2604
E-mail: ciac@llnl.gov
For emergencies and off-hour assistance, DOE, DOE contractor sites,
and the NIH may contact CIAC 24-hours a day. During off hours (5PM -
8AM PST), call the CIAC voice number 510-422-8193 and leave a message,
or call 800-759-7243 (800-SKY-PAGE) to send a Sky Page. CIAC has two
Sky Page PIN numbers, the primary PIN number, 8550070, is for the CIAC
duty person, and the secondary PIN number, 8550074 is for the CIAC
Project Leader.
Previous CIAC notices, anti-virus software, and other information are
available from the CIAC Computer Security Archive.
World Wide Web: http://ciac.llnl.gov/
Anonymous FTP: ciac.llnl.gov (198.128.39.53)
Modem access: +1 (510) 423-4753 (28.8K baud)
+1 (510) 423-3331 (28.8K baud)
CIAC has several self-subscribing mailing lists for electronic
publications:
1. CIAC-BULLETIN for Advisories, highest priority - time critical
information and Bulletins, important computer security information;
2. CIAC-NOTES for Notes, a collection of computer security articles;
3. SPI-ANNOUNCE for official news about Security Profile Inspector
(SPI) software updates, new features, distribution and
availability;
4. SPI-NOTES, for discussion of problems and solutions regarding the
use of SPI products.
Our mailing lists are managed by a public domain software package
called Majordomo, which ignores E-mail header subject lines. To
subscribe (add yourself) to one of our mailing lists, send the
following request as the E-mail message body, substituting
ciac-bulletin, ciac-notes, spi-announce OR spi-notes for list-name:
E-mail to ciac-listproc@llnl.gov or majordomo@tholia.llnl.gov:
subscribe list-name
e.g., subscribe ciac-notes
You will receive an acknowledgment email immediately with a confirmation
that you will need to mail back to the addresses above, as per the
instructions in the email. This is a partial protection to make sure
you are really the one who asked to be signed up for the list in question.
If you include the word 'help' in the body of an email to the above address,
it will also send back an information file on how to subscribe/unsubscribe,
get past issues of CIAC bulletins via email, etc.
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
owned rights. Reference herein to any specific commercial products,
process, or service by trade name, trademark, manufacturer, or
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
advertising or product endorsement purposes.
LAST 10 CIAC BULLETINS ISSUED (Previous bulletins available from CIAC)
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H-70: Vulnerability in rpcbind
H-71: Vulnerability in the at(1) program
H-72: SunOS eeprom Vulnerability
H-73: SunOS chkey Vulnerability
H-74: Unix lpr Buffer Overrun Vulnerability
H-75: Solaris Solstice AdminSuite Vulnerabilities
H-76: Netscape Navigator Security Vulnerability
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