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Linux Kernel: Remote DoS vulnerability with IPTables TCP Handling


1.  Gentoo Linux Security Advisory

Version Information

Advisory Reference GLSA 200407-12 / Kernel
Release Date July 14, 2004
Latest Revision October 10, 2004: 02
Impact high
Exploitable remote
Package Vulnerable versions Unaffected versions Architecture(s)
sys-kernel/aa-sources < 2.6.5-r5 >= 2.6.5-r5, < 2.6* All supported architectures
sys-kernel/ck-sources < 2.6.7-r2 >= 2.6.7-r2, < 2.6* All supported architectures
sys-kernel/development-sources < 2.6.8 >= 2.6.8 All supported architectures
sys-kernel/gentoo-dev-sources < 2.6.7-r7 >= 2.6.7-r7 All supported architectures
sys-kernel/hardened-dev-sources < 2.6.7-r1 >= 2.6.7-r1 All supported architectures
sys-kernel/hppa-dev-sources < 2.6.7_p1-r1 >= 2.6.7_p1-r1 All supported architectures
sys-kernel/mips-sources < 2.6.4-r4 >= 2.6.4-r4, < 2.6 All supported architectures
sys-kernel/mm-sources < 2.6.7-r4 >= 2.6.7-r4, < 2.6* All supported architectures
sys-kernel/pegasos-dev-sources < 2.6.7-r1 >= 2.6.7-r1 All supported architectures
sys-kernel/rsbac-dev-sources < 2.6.7-r1 >= 2.6.7-r1 All supported architectures
sys-kernel/uclinux-sources < 2.6.7_p0 >= 2.6.7_p0-r1, < 2.6 All supported architectures
sys-kernel/usermode-sources < 2.6.6-r2 >= 2.6.6-r2, < 2.6 All supported architectures
sys-kernel/win4lin-sources < 2.6.7-r1 >= 2.6.7-r1, < 2.6 All supported architectures
sys-kernel/xbox-sources < 2.6.7-r1 >= 2.6.7-r1, < 2.6 All supported architectures

Warning: *: Needs to be manually updated

Related bugreports: #55694


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.

2.  Impact Information


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.


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.


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.

3.  Resolution Information


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.


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

Code Listing 3.1: Resolution

# 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.

4.  References


Page updated July 14, 2004

Summary: This is a Gentoo Linux Security Advisory

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