[NEWS] 'Malicious-URL' Feature may be Circumvented Using IP Fragmentation in NetScreen

From: support@securiteam.com
Date: 11/27/02

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    From: support@securiteam.com
To: list@securiteam.com
Date: 27 Nov 2002 01:00:22 +0200

    The following security advisory is sent to the securiteam mailing list, and can be found at the SecuriTeam web site: http://www.securiteam.com
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      'Malicious-URL' Feature may be Circumvented Using IP Fragmentation in
    NetScreen
    ------------------------------------------------------------------------

    SUMMARY

    In response to the Code-Red events in the winter of 2001/2002 NetScreen
    added a feature to its firewalls that can be used to block access to given
    URLs on external web servers. This feature was designed to assist network
    administrators quickly restrict access to web content until a more
    thorough solution could be implemented.

    A vulnerability has been discovered in the implementation of this
    'Malicious-URL' blocking feature that could allow an http client to bypass
    the screening and view a protected URL. By carefully fragmenting the URL
    in the http header into many IP fragments, the feature could be
    circumvented.

    DETAILS

    Vulnerable systems:
     * ScreenOS 2.7.1
     * ScreenOS 2.8
     * ScreenOS 3.0
     * ScreenOS 3.1
     * ScreenOS 4.0

    Immune systems:
     * ScreenOS 4.01

    Recommended Actions:
    Any or all of

    (1) Upgrade to ScreenOS 4.0.1 or later

    (2) Minimize the time that Malicious-URLs are defined on the firewall

    (3) Install all vendor patches on at-risk servers when released

    How to Get ScreenOS:
    If you have registered your product with NetScreen and have a valid
    service contract, you can simply download the software from:
    <http://www.netscreen.com/support/updates.html>
    http://www.netscreen.com/support/updates.html

    You will be prompted for your User ID and Password. Enter the whole or
    part of your company name as your User ID and enter your registered
    NetScreen device serial number as the password.

    If you have not yet registered your product with NetScreen, you will need
    to contact NetScreen Technical Support for special instructions on how to
    obtain the fixed software. NetScreen Technical Support is available 24
    hours a day, 365 days a year. Contact information can be located at
    <http://www.netscreen.com/support/technical_assistance.html>
    http://www.netscreen.com/support/technical_assistance.html

    Please reference this Advisory title as evidence of your entitlement to
    the fixed software version.

    NetScreen authorized Value Added Resellers have access to NetScreen
    software versions and may also be a channel through which to obtain the
    new release.

    ADDITIONAL INFORMATION

    The information has been provided by
    <mailto:security-alert@netscreen.com> NetScreen Security Response Team.

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