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Published:

08 July 1997

Protect yourself against future threats.

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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
directly.

Previous advisories and external security bulletins can be retrieved from:

	http://www.auscert.org.au/information/advisories.html

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: auscert@auscert.org.au
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
                           ___  __ __    _     ___
                          /       |     /_   /
                          \___  __|__  /     \___
          __________________________________________________________

                             INFORMATION BULLETIN

                  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.
______________________________________________________________________________


Introduction

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.

Problem

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
message size.

Solution

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-
ately.

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:

ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/usa/nt40/hotfixes-
postSP3/icmp-fix

Windows 95:

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:

ftp://ftp.microsoft.com/Softlib/MSLFILES/vipupd.exe

______________________________________________________________________________

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
    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)

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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