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From: X-Force (xforceiss.net)
Date: Tue Apr 30 2002 - 13:59:20 CDT

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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 xforceiss.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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