A security vulnerability discovered in the Linux kernel earlier this week leaves the OS vulnerable to communication from IP addresses previously blocked by firewalls.

The flaw affects kernel versions 2.4.14 to 2.4.18-pre9 and, more specifically, a component of the Netfilter firewall software, which was recently included in the kernel.

The vulnerability affects users of IRC (Internet Relay Chat). Because the IRC program configures its firewall setting too broadly, it allows through packets from IP addresses that may have been blocked by Netfilter.

The Netfilter team released a security advisory which can be found here.

Linux distributor Red Hat also released an advisory warning that versions 7.1 and 7.2 of its software are vulnerable, although the flawed software isn't installed by default. This can be found here.