AUSCERT External Security Bulletin Redistribution

                       ESB-2002.207 -- ISS Advisory
    Remote Denial of Service Vulnerability in RealSecure Network Sensor
                                1 May 2002


        AusCERT Security Bulletin Summary

Product:                RealSecure Network Sensor 5.x, XPU 3.4 and later
                        RealSecure Network Sensor 6.0, XPU 3.4 and later
                        RealSecure Network Sensor 6.5
Vendor:                 Internet Security Systems (ISS)
Impact:                 Denial of Service
Access Required:        Remote

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Internet Security Systems Security Advisory
April 30, 2002

Remote Denial of Service Vulnerability in RealSecure Network Sensor


ISS X-Force has learned of a denial of service (DoS) vulnerability that
affects Internet Security Systems RealSecure Network Sensor. This
vulnerability may allow remote attackers to crash RealSecure by sending
specially crafted packets to network segments monitored by RealSecure.
RealSecure X-Press Update 4.3 contains a fix for the DHCP vulnerability
and is available for immediate download on the ISS download center.

Affected Versions:

RealSecure Network Sensor 5.x, XPU 3.4 and later
RealSecure Network Sensor 6.0, XPU 3.4 and later
RealSecure Network Sensor 6.5


RealSecure Network Sensor has three informational signatures associated
with DHCP (Dynamic Host Configuration Protocol): DHCP_ACK (7131),
DHCP_Discover (7132), and DHCP_Request (7133). These signatures contain
a flaw that will result in an illegal attempt to de-reference a null
memory pointer when RealSecure detects certain types of DHCP traffic.
This action may generate an exception error or a segmentation fault
which can cause the RealSecure sensor to crash. This vulnerability was
introduced in RealSecure Network Sensor 6.5. XPU 3.4 delivered the
vulnerable DHCP signatures to older RealSecure product lines including
6.0 and 5.x.

It may be possible for remote attackers to create specially-crafted DHCP
traffic to cause the sensor to malfunction or crash entirely. The three
DHCP signatures were disabled by default in Network Sensor 5.x and 6.0.
The signatures were enabled by default in Network Sensor 6.5 within the
"Maximum" policy. However, if these signatures are not enabled,
RealSecure Network Sensor is not vulnerable to these attacks.


X-Force recommends that all RealSecure customers tune their policies to
their environments. RealSecure X-Press Update 4.3 contains a fix for the
DHCP vulnerability. X-Press Update 4.3 is available for download on the
ISS download center:  http://www.iss.net/download/.

DHCP traffic is commonly blocked at perimeter firewalls. Network
administrators are advised to assess their network perimeter defenses
routinely. Exploitation of this vulnerability is blocked by proper
filtering of DHCP traffic on UDP port 67.


About Internet Security Systems (ISS)
Founded in 1994, Internet Security Systems (ISS) (Nasdaq: ISSX) is a
pioneer and world leader in software and services that protect critical
online resources from an ever-changing spectrum of threats and misuse.
Internet Security Systems is headquartered in Atlanta, GA, with
additional operations throughout the Americas, Asia, Australia, Europe
and the Middle East.

Copyright (c) 2002 Internet Security Systems, Inc. All rights reserved

Permission is hereby granted for the electronic redistribution of this
document. It is not to be edited or altered in any way without the
express written consent of the Internet Security Systems X-Force. If you
wish to reprint the whole or any part of this document in any other
medium excluding electronic media, please email xforce@iss.net for

Disclaimer: The information within this paper may change without notice.
Use of this information constitutes acceptance for use in an AS IS
condition. There are NO warranties, implied or otherwise, with regard to
this information or its use. Any use of this information is at the
user's risk. In no event shall the author/distributor (Internet Security
Systems X-Force) be held liable for any damages whatsoever arising out
of or in connection with the use or spread of this information.

X-Force PGP Key available on MIT's PGP key server and PGP.com's key
as well as at http://www.iss.net/security_center/sensitive.php

Please send suggestions, updates, and comments to: X-Force

Version: 2.6.2


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