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Gentoo Linux Security Advisory                           GLSA 200407-12
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                                            http://security.gentoo.org/
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  Severity: High
     Title: Linux Kernel: Remote DoS vulnerability with IPTables TCP
            Handling
      Date: July 14, 2004
      Bugs: #55694
        ID: 200407-12

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Synopsis
========

A flaw has been discovered in 2.6 series Linux kernels that allows an
attacker to send a malformed TCP packet, causing the affected kernel
to possibly enter an infinite loop and hang the vulnerable machine.

Background
==========

The Linux kernel is responsible for managing the core aspects of a
GNU/Linux system, providing an interface for core system applications
as well as providing the essential structure and capability to access
hardware that is needed for a running system.

Affected packages
=================

    -------------------------------------------------------------------
     Kernel                /    Unaffected    /                Remerge
    -------------------------------------------------------------------
  1  aa-sources ............... >= 2.6.5-r5 ...................... YES
  2  ck-sources ............... >= 2.6.7-r2 ...................... YES
  3  gentoo-dev-sources ....... >= 2.6.7-r7 ..........................
  4  hardened-dev-sources ..... >= 2.6.7-r1 ..........................
  5  hppa-dev-sources ....... >= 2.6.7_p1-r1 .........................
  6  mips-sources ............ *>= 2.6.4-r4 ..........................
     .......................... >= 2.6.7-r1 ..........................
  7  mm-sources ............... >= 2.6.7-r4 ...................... YES
  8  pegasos-dev-sources ...... >= 2.6.7-r1 ..........................
  9  rsbac-dev-sources ........ >= 2.6.7-r1 ..........................
 10  uclinux-sources ........ >= 2.6.7_p0-r1 .........................
 11  usermode-sources ......... >= 2.6.6-r2 ..........................
 12  win4lin-sources .......... >= 2.6.7-r1 ..........................
 13  xbox-sources ............. >= 2.6.7-r1 ..........................
 14  development-sources ...... Vulnerable! ..........................
    -------------------------------------------------------------------
     NOTE: Some kernels are still vulnerable. Users should migrate to
           another kernel if one is available or seek another
           solution such as patching their existing kernel.
    -------------------------------------------------------------------
     NOTE: Packages marked with "Remerge" as "YES" require a
 re-merge
           even though Portage does not indicate a newer version!
    -------------------------------------------------------------------
     14 affected packages on all of their supported architectures.
    -------------------------------------------------------------------

Description
===========

An attacker can utilize an erroneous data type in the IPTables TCP
option handling code, which lies in an iterator. By making a TCP packet
with a header length larger than 127 bytes, a negative integer would be
implied in the iterator.

Impact
======

By sending one malformed packet, the kernel could get stuck in a loop,
consuming all of the CPU resources and rendering the machine useless,
causing a Denial of Service. This vulnerability requires no local
access.

Workaround
==========

If users do not use the netfilter functionality or do not use any
``--tcp-option'' rules they are not vulnerable to this exploit. Users
that are may remove netfilter support from their kernel or may remove
any ``--tcp-option'' rules they might be using. However, all users are
urged to upgrade their kernels to patched versions.

Resolution
==========

Users are encouraged to upgrade to the latest available sources for
their system:

    # emerge sync
    # emerge -pv your-favorite-sources
    # emerge your-favorite-sources

    # # Follow usual procedure for compiling and installing a kernel.
    # # If you use genkernel, run genkernel as you would do normally.

Availability
============

This GLSA and any updates to it are available for viewing at
the Gentoo Security Website:

    http://security.gentoo.org/glsa/glsa-200407-12.xml

Concerns?
=========

Security is a primary focus of Gentoo Linux and ensuring the
confidentiality and security of our users machines is of utmost
importance to us. Any security concerns should be addressed to
security@gentoo.org or alternatively, you may file a bug at
http://bugs.gentoo.org.

License
=======

Copyright 2004 Gentoo Foundation, Inc; referenced text
belongs to its owner(s).

The contents of this document are licensed under the
Creative Commons - Attribution / Share Alike license.

http://creativecommons.org/licenses/by-sa/1.0