Researchers at Neohapsis Labs have discovered an ingeniously simple man-in-the-middle attack that can hijack the IPv6 capability of a PC to silently intercept all web traffic on a target network.

Due for full disclosure at the DEF CON 21 conference, the attack’s design isn’t new – the similar Stateless Address Auto Configuration (SLAAC) principle was demonstrated at Infosec in 2011 – but extends it to Windows 8 segments for the first time.

Assuming only an available IPv4 address on the network, the team were able to use a ‘Sudden Six’ script run from a Linux host to rapidly insert the system as a rogue IPv6 router. This IPv6 overlay was able to intercept all traffic travelling through it, which is to say all traffic on that network.

It’s not clear from the description how easy this shadow routing would be to detect on the established IPv4 infrastructure, but in theory the attack would be invisible. Although the team tested in against Windows 8 clients, it would work against any PC that helpfully enables IPv6 support by default, which includes many business and all consumer systems using Windows 7 onwards.

Ironically, the major limitation of the attack is that it wouldn’t work against the tiny number of networks that natively route IPv6 traffic, in which case the overlay would fail. Only IPv4 networks are vulnerable.

Another more manual defence is to disable IPv6 support on the network interface cards of every PC, although Neohapsis points out that this approach might defeat efforts to boost its uptake.

“To boil it down, attackers can conceivably (and fairly easily) weaponize an attack on our systems simply by leveraging this vulnerability,” said Neohapsis lab head, Scott Behrens. “They could pretend to be an IPv6 router on your network and see all your web traffic, including data being sent to and from your machine.”

Worse still, “the attacker could modify web pages to launch client-side attacks, meaning they could create fake websites that look like the ones you are trying to access, but send all data you enter back to the attacker (such as your username and password or credit card number).”

Ideally, a more in-depth defence against the attack would be something along the lines of Cisco’s ‘first hop’ security in which the trusted IPv6 router port is advertise (see RFC 6105 for details), said Behrens.

The firm said it would publish the Sudden Six tool after the Friday presentation.