Linux Kernel: Remote DoS vulnerability with IPTables TCP Handling

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.

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.