[Full-Disclosure] iDEFENSE Security Advisory 03.02.04: FreeBSD Memory Buffer Exhaustion Denial of Service Vulnerability

idlabs-advisories_at_idefense.com
Date: 03/02/04

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Date: Tue, 2 Mar 2004 13:37:41 -0500

    FreeBSD Memory Buffer Exhaustion Denial of Service Vulnerability

    iDEFENSE Security Advisory 03.02.04
    www.idefense.com/application/poi/display?id=78&type=vulnerabilities
    March 02, 2004

    I. BACKGROUND

    Free BSD is a free, Open Source unix operating system. More information
    is available at http://www.freebsd.org/.

    II. DESCRIPTION

    Remote exploitation of a denial of service (DoS) vulnerability in
    FreeBSD's memory buffers (mbufs) could allow attackers to launch a DoS
    attack.

    By sending many out-of-sequence packets, a low bandwidth denial of
    service attack is possible against FreeBSD. When the targeted system
    runs out of memory buffers (mbufs), it is no longer able to accept or
    create new connections.

    III. ANALYSIS

    Exploitation of this vulnerability requires that the targeted system has
    at least one open TCP port.

    The DoS will last until the port is closed, either by the attacker or
    the target machine.

    iDEFENSE has proof of concept exploit code demonstrating the impact of
    this vulnerability.

    IV. DETECTION

    iDEFENSE has confirmed that this vulnerability exists in FreeBSD 5.1
    (default install from media). FreeBSD has stated that all versions are
    affected.

    V. WORKAROUND

    "It may be possible to mitigate some denial-of-service attacks by
    implementing timeouts at the application level."

    VI. VENDOR RESPONSE

    "Do one of the following:

    1) Upgrade your vulnerable system to 4-STABLE, or to the RELENG_5_2,
    RELENG_4_9, or RELENG_4_8 security branch dated after the correction
    date.

    OR

    2) Patch your present system:

    The following patch has been verified to apply to FreeBSD 4.x and 5.x
    systems.

    a) Download the relevant patch from the location below, and verify the
    detached PGP signature using your PGP utility.

    [FreeBSD 5.2] # fetch
    ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/tcp52.patch # fetch
    ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/tcp52.patch.asc

    [FreeBSD 4.8, 4.9] # fetch
    ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/tcp47.patch # fetch
    ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/tcp47.patch.asc

    b) Apply the patch.

    # cd /usr/src # patch < /path/to/patch

    c) Recompile your kernel as described in
    <URL:http://www.freebsd.org/handbook/kernelconfig.html> and reboot the
    system."

    VII. CVE INFORMATION

    The Common Vulnerabilities and Exposures (CVE) project has assigned the
    name CAN-2004-0171 to this issue. This is a candidate for inclusion in
    the CVE list (http://cve.mitre.org), which standardizes names for
    security problems.

    VIII. DISCLOSURE TIMELINE

    January 22, 2004 Exploit acquired by iDEFENSE
    February 17, 2004 iDEFENSE clients notified
    February 18, 2004 Initial vendor notification
    February 18, 2004 Initial vendor response
    March 02, 2004 Coordinated public disclosure

    IX. LEGAL NOTICES

    Copyright (c) 2004 iDEFENSE, Inc.

    Permission is granted for the redistribution of this alert
    electronically. It may not be edited in any way without the express
    written consent of iDEFENSE. If you wish to reprint the whole or any
    part of this alert in any other medium other than electronically, please
    email customerservice@idefense.com for permission.

    Disclaimer:
    The information in the advisory is believed to be accurate at the time
    of publishing based on currently available information. Use of the
    information constitutes acceptance for use in an AS IS condition. There
    are no warranties with regard to this information. Neither the author
    nor the publisher accepts any liability for any direct, indirect, or
    consequential loss or damage arising from use of, or reliance on, this
    information.

    _______________________________________________
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    Charter: http://lists.netsys.com/full-disclosure-charter.html

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