Operating system flaw opens security vulnerability

A flaw in several versions of the OpenBSD operating system could give attackers complete control over vulnerable machines

Several recent versions of the popular OpenBSD operating system contain a remotely exploitable buffer overrun vulnerability that security experts say could give attackers complete control over vulnerable machines.

The security flaw was found in OpenBSD's kernel and involves the way the OS handles certain kinds of IPv6 packets, according to the researchers at Core Security Technologies Inc. who discovered the problem. The security vulnerability affects versions 3.1, 3.6, 3.8, 3.9, 4.0 and 4.1 of OpenBSD. Also, all other versions that support the IPv6 stack are thought to be vulnerable.

The OpenBSD team has released a patch and a workaround for the flaw . Because this is a kernel-level security vulnerability, administrators will need to rebuild their kernels after installing the patch.

In order to exploit the security flaw, an attacker need only be able to send fragmented IPv6 packets to a target system. This requires direct access to the target network, however the attacker's machine does not need to have its own IPv6 stack in order to make the exploit work, Core said. Users who don't need to route IPv6 traffic can block those packets using OpenBSD's native firewall.

Ivan Arce, chief technology officer of Boston-based Core, said that once an attacker knows what he is looking for, exploiting this vulnerability is trivial.

"It was difficult for us to spot and figure out what was going on because the kernel was crashing in a bunch of different places because the memory was corrupted," Arce said. "Once we figured it out, it's not difficult to exploit."

This is the first IPv6-related security vulnerability that leads to a remote system compromise that Core has seen, Arce said, but it's unlikely to be the last.

"It's a complex protocol and some of the implementations are difficult," he said. "When things are that complex, it's likely you will run into security vulnerabilities as well."

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