DOCUMENT:Q154460
TITLE   :Denial of Service Attack Against WinNT Simple TCP/IP Services
PRODUCT :Microsoft Windows NT
PROD/VER:4.0
OPER/SYS:WINDOWS
KEYWORD :kbbug4.00 kbfile kbfix4.00 kbnetwork NTSrvWkst nttcp

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The information in this article applies to:

 - Microsoft Windows NT Workstation version 4.0
 - Microsoft Windows NT Server version 4.0
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SYMPTOMS
========

As your computer is being attacked there may be a jump in bandwidth
utilization on a subnet containing Windows NT computers and performance may
suffer. A network analyzer shows a large amount of UDP traffic, typically
from port 19 (chargen).

CAUSE
=====

A malicious attack may be mounted against Windows NT computers with the
Simple TCP/IP Services installed. The attack consists of a flood of UDP
datagrams sent to the subnet broadcast address with the destination port
set to 19 and a spoofed source IP address. The Windows NT computers running
Simple TCP/IP services respond to each broadcast, creating a flood of UDP
datagrams.

RESOLUTION
==========

Windows NT TCP/IP, Windows Sockets, and Simple TCP/IP services have been
modified to be more attack resistant. Windows Sockets now supports a new
socket option, SO_BROADCAST, that can be set to allow the recvfrom() call
to pass broadcast datagrams to the application. The default for this option
is OFF. Previous implementations passed broadcasts datagrams to any Windows
Sockets application that issued a recvfrom() call. Additionally, the
chargen service and other Simple TCP/IP services have been modified to drop
any datagrams that have the source port equal to the destination port to
prevent "looping" attacks.

To resolve this problem, obtain the hotfix below, or wait for the next
service pack.

This hotfix has been posted to the following Internet location:

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

STATUS
======

Microsoft has confirmed this to be a problem in Windows NT version 4.0.
A supported fix is now available, but has not been fully regression-tested
and should be applied only to systems experiencing this specific problem.
Unless you are severely impacted by this specific problem, Microsoft
recommends that you wait for the next Service Pack that contains this fix.
Contact Microsoft Technical Support for more information.

Additional query words: 4.00 prodnt chargen attack

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