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            AUSCERT External Security Bulletin Redistribution
                                      
                                      
                   ESB-98.031 -- CERT Summary CS-98.02
        Denial of service attacks targeting Windows 95/NT machines
                             5th March 1998

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The CERT Coordination Center has released the following advisory concerning
increasing denial of service attacks targeting a vulnerability in the
Microsoft TCP/IP stack.  This DoS attack can cause the targeted machines
to halt or crash.

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.

NOTE: This is only the original release of the security bulletin.  It will
not be updated when the original bulletin is.  If downloading at a later
date, it is recommended that the bulletin is retrieved from the original
authors to ensure that the information is still current.

Contact information for CERT/CC 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
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.
Facsimile:      (07) 3365 7031


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CERT* Summary CS-98.02 - SPECIAL EDITION
March 4, 1998


This special edition of the CERT Summary reports denial of service attacks
targeting a vulnerability in the Microsoft TCP/IP stack.

Past CERT Summaries are available from 
     ftp://ftp.cert.org/pub/cert_summaries/

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Denial of service attacks targeting Windows 95/NT machines
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This special edition of the CERT Summary reports denial of service attacks
targeting a vulnerability in the Microsoft TCP/IP stack. We have received
reports from a number of sites and incident response teams indicating that a
large number of machines were affected.

The attacks involve sending a pair of malformed IP fragments which are
reassembled into an invalid UDP datagram. The invalid UDP datagram causes the
target machine to go into an unstable state. Once in an unstable state, the
target machine either halts or crashes. We have received reports that some
machines crashed with a blue screen while others rebooted.

Attack tools known by such names as NewTear, Bonk, and Boink have been
previously used to exploit this vulnerability against individual hosts;
however, in this instance, the attacker used a modified tool to automatically
attack a large number of hosts.

The solution to protect Windows 95 and NT machines from this attack is to
apply the appropriate Microsoft patch. The Microsoft patch, as well as more
information about the vulnerability, can be found in the January 1998
Microsoft Market Bulletin entitled, "New Teardrop-like TCP/IP Denial of
Service Program" available from:

        http://www.microsoft.com/security/newtear2.htm

Although the first instance of this attack, which started March 2, 1998
appears to be over, keep in mind that the tools to launch this attack are now
available and we expect to see more incidents of this type.


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How to Contact the CERT Coordination Center

Email    cert@cert.org 

Phone    +1 412-268-7090 (24-hour hotline) 
                CERT personnel answer on business days
                8:30-5:00 p.m. EST (GMT-5)/EDT(GMT-4), 
                and are on call for emergencies during
                other hours.

Fax      +1 412-268-6989

Postal address
        CERT Coordination Center
        Software Engineering Institute
        Carnegie Mellon University
        Pittsburgh PA 15213-3890
        USA

To be added to our mailing list for CERT advisories and bulletins, send your
email address to 
        cert-advisory-request@cert.org
In the subject line, type
        SUBSCRIBE your-email-address

CERT advisories and bulletins are posted on the USENET news group
         comp.security.announce

CERT publications, information about FIRST representatives, and other
security-related information are available for anonymous FTP from
        http://www.cert.org/
        ftp://ftp.cert.org/pub/

If you wish to send sensitive incident or vulnerability information to CERT
staff by electronic mail, we strongly advise you to encrypt your message.
We can support a shared DES key or PGP. Contact the CERT staff for more
information. 

Location of CERT PGP key
         ftp://ftp.cert.org/pub/CERT_PGP.key

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Copyright 1998 Carnegie Mellon University. Conditions for use, disclaimers,
and sponsorship information can be found in
http://www.cert.org/legal_stuff.html and ftp://ftp.cert.org/pub/legal_stuff .
If you do not have FTP or web access, send mail to cert@cert.org with
"copyright" in the subject line.
 
* CERT is registered in the U.S. Patent and Trademark Office.

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