OpenBSD hit by 'critical' IPv6 flaw

A security hole in the way OpenBSD handles IPv6 data packets exposes systems running the open-source OS to serious attack.

A vulnerability in the way OpenBSD handles IPv6 data packets exposes systems running the traditionally secure open-source operating system to serious attack.

A memory corruption vulnerability error exists in the OpenBSD code that handles IPv6 packets, Core Security Technologies said in an alert published Tuesday. Exploiting the flaw could let an attacker commandeer a vulnerable system, according to Core, which said it discovered the issue and crafted sample exploit code.

"This vulnerability allows attackers to gain complete control of the target system, bypassing all the operating system's security mechanisms," Core said in a statement Wednesday. Core deems the issue "critical." Security-monitoring company Secunia rates it "highly critical."

OpenBSD is one of several operating systems based on the Berkeley Software Distribution, or BSD. The most popular BSD descendents are FreeBSD, PCBSD and NetBSD, with OpenBSD coming in fourth, according to the BSDstats project.

OpenBSD is mostly known for its security enhancements and is used for firewalls, intrusion detection systems and other applications. Google is among OpenBSD users and backers. The OpenBSD team likes to tout that only a few remotely exploitable vulnerabilities have been found in the code in a decade.

A security update was issued last week to deal with the OpenBSD issue, which affects .

Default installations of OpenBSD are vulnerable as IPv6 is enabled and the system does not filter inbound packets, Core said. IPv6 is the next version of the Internet Protocol designed to support a broader range of IP addresses as the IP version 4 addresses currently in use become more scarce.

To exploit the vulnerability, an attacker must have the ability to send malicious IPv6 packets to the target system or be on the same network, Symantec said in an alert. The Cupertino, Calif., security company raised its ThreatCon to level 2 because of the issue, which means attacks are expected.

As a work-around for users who can not apply the OpenBSD patch or who do not need to process or route IPv6 traffic on their systems, all inbound IPv6 packets can be blocked by using Openness' firewall.

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