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Netgear confirms: Intel's wobbly Puma 6 in fast broadband modems is super-easy to choke out

No fix ready yet for DoS-able home gateways

By Shaun Nichols, 1 May 2017

Netgear has warned customers about the trivial denial-of-service vulnerability discovered in its Intel-powered gigabit cable modems.

The networking biz is advising owners of the CM700 gateway to sit tight while it figures out how to patch a weakness that leaves the modem prone to DoS attacks. In other words, there is no workaround right now.

"Netgear is aware of a security vulnerability that can potentially allow an attacker to slow or stop your network access," the advisory reads. "This vulnerability does not pose a risk for data loss or access to your network."

We understand Intel Security is also looking into the matter, with a potential firmware fix on the horizon, and a CVE allocation for the flaw is forthcoming.

The issue, which The Register reported on last week with proof-of-concept exploit code, is actually the result of a flaw in the Intel Puma 6 chipset Netgear uses for the CM700.

Netizens have found that the hardware is prone to suffering from massively degraded performance when sent a stream of small, or zero-sized, TCP or UDP packets spread over multiple IP network ports.

Every time one of these packets comes in, the chipset keeps a record of it in a look-up table. By hitting a large range of ports at once – say with three to five thousand packets a second – it is possible to fill up this table, and cripple the device's performance. This leaves the victim with slow web browsing, and huge latency spikes ruining online gaming, and so on.

One engineer described to us the condition as being "trivial" to exploit once the attacker has the public IP address of the target modem. In other words, once you know the IP address of someone using a Puma 6-powered modem, you can easily blast them off the internet. There thousands upon thousands of people using modems with Intel's chipset – from Comcast Xfinity subscribers in the US to Virgin Media Super Hub 3 owners in the UK.

Therefore, a number of other vendors who use Intel's Puma 6 chipset are also going to be vulnerable until a patch can be developed and deployed.

The flaw is linked to some of the ongoing latency complaints surrounding Puma 6-equipped cable modems, many of which have been sold for use with expensive gigabit cable internet packages. And there is a pending class-action lawsuit against Arris – another vendor using Intel's crocked chipset. ®

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