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Experts scramble to quash IPv6 flaw

'Can be exploited by any greedy Estonian teenager with a $300 Linux machine'

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A flawed feature that could amplify denial-of-service attacks on next-generation networks has vendors and engineers rushing to eliminate the potential security issue.

This week, experts sent two drafts to the Internet Engineering Task Force (IETF) - the technical standards-setting body for the internet - proposing different ways of fixing a problem in the way that Internet Protocol version 6 (IPv6) allows the source of network data to determine its path through the network. The drafts recommend that the IPv6 feature should either be eliminated or, at the very least, disabled by default.

The specification, known as the Type 0 Routing Header (RH0), allows computers to tell IPv6 routers to send data by a specific route. Originally envisioned as a way to let mobile users to retain a single IP for their devices, the feature has significant security implications. During a presentation at the CanSecWest conference on 18 April, researchers Philippe Biondi and Arnaud Ebalard pointed out that RH0 support allows attackers to amplify denial-of-service attacks on IPv6 infrastructure by a factor of at least 80.

"In rough terms, it makes everything we thought was bad, a thousand times worse," Paul Vixie, president of the Internet Systems Consortium, said in an email interview with SecurityFocus. "It can be exploited by any greedy Estonian teenager with a $300 Linux machine."

The security issues comes as more organisations are making the switch to IPv6 from the current internet routing standard (IPv4). The US federal government and many major corporations are transitioning to the standard by the end of the decade. The US Department of Defense and the White House's Office of Management and Budget have mandated that the military services and federal agencies move their backbone systems to IPv6 by 30 June, 2008.

However, the standard is already widely supported by routers and operating systems. Apple's Mac OS X, the Linux operating systems, and Microsoft's next-generation operating system, Vista, uses the standard as the default networking protocol. Microsoft supports wrapping IPv6 packets inside of IPv4 data, known as 6to4 tunneling, so that networks sending data using IPv6 can communicate across the Internet, but attackers could use the technique to send covert data.

The RH0 security issues has its roots in the current internet protocol implementation. The specification for IPv4 allows the sender of data to specify one or more routers through which the data must travel. Known as source routing, the technique allows up to nine other addresses to be included in an IPv4's extended header, requesting that the packet be routed through those specific addresses. While source routing can be beneficial for diagnostics, it can also be used to amplify a denial-of-service attack by a factor of 10 by alternating two target Internet addresses in the header, ping-ponging the data between two machines.

While source routing has been accepted as a bad security risk by most companies and most routers disable the feature by default, the IETF has not eliminated the option from the specification and extended it to IPv6.

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