Forwarded From: Microsoft Product Security <secnotif@MICROSOFT.COM>
Microsoft Security Bulletin (MS98-014)
---------------------------------------------------------------------------
Update available for RPC Spoofing Denial of Service on Windows NT
Originally Posted: September 29, 1998
Last Revised: September 29, 1998
Summary
=======
Microsoft has released a patch that enhances the way that Windows NT
processes bad Remote Procedure Call (RPC) datagrams. This patch prevents a
malicious attack in which an attacker sends an RPC datagram to a server and
spoofs the return address so that the datagram appears to have come from
another server. This tricks the two servers into erroneously sending RPC
error messages to each other. These error messages could cause a temporary
loop resulting in high CPU utilization and network bandwidth until the bad
packets are discarded.
Customers using affected software listed below should evaluate risks to
their systems posed by this issue, then download and apply this patch as
appropriate to their configurations.
Issue
=====
It is possible for a malicious attacker to send spoofed RPC datagrams to UDP
destination port 135 so that it appears as if one RPC server sent bad data
to another RPC server. The second server returns a REJECT packet and the
first server (the spoofed server) replies with another REJECT packet
creating a loop that is not broken until a packet is dropped, which could
take a few minutes. If this spoofed UDP packet is sent to multiple
computers, a loop could possibly be created, consuming processor resources
and network bandwidth.
While there have not been any reports of customers being adversely affected
by these problems, Microsoft is releasing a patch to address any risks posed
by this issue.
Affected Software Versions
==========================
The following software is affected by this vulnerability:
- Microsoft (R) Windows NT (R) Workstation version 4.0
- Microsoft Windows NT Server version 4.0
- Microsoft Windows NT Server version 4.0, Terminal Server Edition
What Microsoft is Doing
=======================
On September 29th Microsoft released a patch that changes the behavior of
the RPC service so it can better detect spoofed packets and not respond to
them, preventing an attack of this type from causing any problem.
Microsoft has sent this security bulletin to customers
subscribing to the Microsoft Product Security Notification
Service (see http://www.microsoft.com/security/bulletin.htm
for more information about this free customer service).
Microsoft has published the following Knowledge Base (KB) articles on this
issue:
- Microsoft Knowledge Base (KB) article Q193233,
RPCSS.EXE Consumes 100% CPU due to RPC-spoofing Attack
http://support.microsoft.com/support/kb/articles/q193/2/33.asp
(Note: It might take 24 hours for the KB article to be visible in the
Web-based Knowledge Base. A copy of the article is also available on the FTP
server in the same directory as the fix.)
What customers should do
========================
Microsoft recommends that customers using affected software listed above
should evaluate risks to their systems posed by this issue, then download
and apply this patch as appropriate to their configuration.
Fix for Windows NT 4.0 x86 version -
- ftp://ftp.microsoft.com/bussys/winnt/winnt-public/
fixes/usa/nt40/hotfixes-postSP3/snk-fix/snk-fixi.exe
Fix for Windows NT 4.0 Alpha version -
- ftp://ftp.microsoft.com/bussys/winnt/winnt-public/
fixes/usa/nt40/hotfixes-postSP3/snk-fix/snk-fixa.exe
Fix for Windows NT Server 4.0, Terminal Server Edition - This fix will be
available shortly. It will be available in the following location:
- ftp://ftp.microsoft.com/bussys/winnt/winnt-public/
fixes/usa/NT40TSE/hotfixes-postSP3/Snk-fix/
(NOTE: The URLs above have been wrapped for readability)
Additional Details
==================
The following are additional notes about this issue:
- It is relatively easy to detect a malicious attack
of this kind by using a network analyzer to watch for
bad RPC packets. Also, during an attack, the RPCSS.EXE
service will consume a very large amount of CPU cycles
(during an active, on-going attack, it will consume
100% of CPU cycles.)
- Systems that are currently in an error loop (sending
error messages back and forth) will recover by themselves
shortly after the attacker has stopped sending spoofed packets.
- If two systems are currently in an error loop (sending
error messages back and forth) momentarily disconnecting
one system from the network will cause an end to that loop,
since UDP packets are connectionless.
- These error packets are addressed to UDP port 135 and can
be filtered at a corporate firewall to protect against
external attackers.
More Information
================
Please see the following references for more information related to this
issue.
- Microsoft Security Bulletin MS98-014, Update available for
RPC Spoofing Denial of Service on Windows NT, (the Web posted
version of this bulletin),
http://www.microsoft.com/security/bulletins/ms98-014.htm
- Microsoft Knowledge Base (KB) article Q193233,
RPCSS.EXE Consumes 100% CPU due to RPC-spoofing Attack
http://support.microsoft.com/support/kb/articles/q193/2/33.asp
(Note: It might take 24 hours for the KB article to be visible in the
Web-based Knowledge Base. A copy of the article is also available on the FTP
server in the same directory as the fix.)
Acknowledgements
================
Microsoft wishes to acknowledge the contributions of
Internet Security Systems, Inc. (http://www.iss.net)
for reporting this problem to us.
Revisions
=========
- September 29, 1998: Bulletin Created
For additional security-related information about Microsoft
products, please visit http://www.microsoft.com/security
---------------------------------------------------------------------------
THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS"
WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER
EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS
FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS
SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT,
INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN
IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR
LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE
FOREGOING LIMITATION MAY NOT APPLY.
(C) 1998 Microsoft and/or its suppliers. All rights reserved.
For Terms of Use see http://support.microsoft.com/support/misc/cpyright.asp.
*******************************************************************
You have received this e-mail bulletin as a result of your registration
to the Microsoft Product Security Notification Service. You may
unsubscribe from this e-mail notification service at any time by sending
an e-mail to MICROSOFT_SECURITY-SIGNOFF-REQUEST@ANNOUNCE.MICROSOFT.COM
The subject line and message body are not used in processing the request,
and can be anything you like.
For more information on the Microsoft Security Notification Service
please visit http://www.microsoft.com/security/bulletin.htm. For
security-related information about Microsoft products, please visit the
Microsoft Security Advisor web site at http://www.microsoft.com/security.
-o-
Subscribe: mail majordomo@repsec.com with "subscribe isn".
Today's ISN Sponsor: Repent Security Incorporated [www.repsec.com]
Received on Mon Oct 5 08:49:50 1998