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AUSCERT External Security Bulletin Redistribution
ESB-97.082 -- CIAC Bulletin H-78
ICMP Vulnerability in Windows 95 and NT 4.0
9 July 1997
The U.S. Department of Energy Computer Incident Advisory Capability has
released the following advisory concerning a vulnerability in the IP stack
in Microsoft Windows 95 and NT 4.0. This vulnerability may allow a remote
user to cause a networked local machine to be made unresponsive and to
require a reboot.
The following security bulletin is provided as a service to AUSCERT's
members. As AUSCERT did not write this document, AUSCERT has had no
control over its content. As such, the decision to use any or all of this
information is the responsibility of each user or organisation, and should
be done so in accordance with site policies and procedures.
Contact information for CIAC is included in the Security Bulletin below.
If you have any questions or need further information, please contact them
Previous advisories and external security bulletins can be retrieved from:
If you believe that your system has been compromised, contact AUSCERT or your
representative in FIRST (Forum of Incident Response and Security Teams).
Internet Email: email@example.com
Facsimile: (07) 3365 4477
Telephone: (07) 3365 4417 (International: +61 7 3365 4417)
AUSCERT personnel answer during Queensland business hours
which are GMT+10:00 (AEST).
On call after hours for emergencies.
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The U.S. Department of Energy
Computer Incident Advisory Capability
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ICMP vulnerability in Windows 95 and NT 4.0
July 3, 1997 20:00 GMT Number H-78
PROBLEM: A vulnerability in the IP stack on Microsoft Windows systems
may allow a remote user to cause a networked system to freeze
if exploited ("denial of service").
PLATFORM: Systems running Microsoft Windows 95, Windows NT 4.0
Workstation, and Windows NT 4.0 Server.
DAMAGE: If exploited, a remote user may be able to cause a denial-of-
service on a networked local machine. The machine be made
unresponsive and needs to be rebooted.
SOLUTION: Apply vendor patches described below.
VULNERABILITY Details of this exploit have been made publicly available and
ASSESSMENT: an attack can be successfully executed remotely.
A vulnerability exists in Microsoft Windows 95 and Windows NT 4.0 Server and
Workstation operating systems that may lead to a frozen (unresponsive) system
if exploited. This denial-of-service attack occurs when a corrupt Internet
Control Message Protocol (ICMP) message is sent to a vulnerable system. A
series of packets are sent to a vulnerable system which is unable to assemble
the packets properly.
The operating system may stop responding because the IP stack is unable to
resolve the IP packet data that has incorrect offset information. Although
this exploit is similar to the Ping of Death attack that appeared earlier this
year, this attack uses ICMP instead of IP packets and is not based solely on
Microsoft has developed a local patch to updated the TCP/IP protocol stack to
correct the problem. Instructions for installing it are available from
Microsoft. CIAC recommends that you update your Emergency Repair Disk immedi-
For Windows NT 4.0 Server and Workstation:
Service Pack 3 must be installed first. Then the ICMP hotfix should be
applied. This file can be downloaded from Microsoft at:
For Windows 95 and OSR2, this issue is resolved by the file VIP.386 version
4.0.956 (6/30/97) and later. This file is included in the self-extracting
VIPUPD.EXE file and can be downloaded from:
CIAC wishes to acknowledge the contributions of Microsoft and Russ Cooper 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: +1 510-422-8193
FAX: +1 510-423-8002
STU-III: +1 510-423-2604
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
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 (22.214.171.124)
Modem access: +1 (510) 423-4753 (28.8K baud)
+1 (510) 423-3331 (28.8K baud)
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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
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LAST 10 CIAC BULLETINS ISSUED (Previous bulletins available from CIAC)
H-68: Windows95 Network Password Vulnerability
H-69: Vulnerability in getopt (3)
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
H-77: Microsoft IIS Boundary Condition Vulnerability
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