Feb 222014

Having had a wee bit of fun at work dealing with an NTP DDoS attack, I feel it is long past time to tackle the root cause of the problem – the ISP’s who have neglected to implement ingress/egress filtering despite it being considered best practice for well over 15 years. Yes, longer than most of us have been connected to the Internet.

It is easy to point at the operators of NTP services that allow their servers to be used as attack amplifiers. And yes these insecure NTP servers should be fixed, but given the widespread deployment of NTP in everything it could take up to a decade for a fix to be universally deployed.

And what then? Before the widespread use of NTP for the amplification distributed denial of service attacks, DNS was commonly used. And after NTP is cleaned up? Or even before? There are other services which can be exploited in the same way.

But the way that amplification attacks are carried out involves two “vulnerabilities”. In addition to the vulnerable service, the attacker forges the packets they send to the vulnerable service so that the replies go back to the victim. Essentially they trick the Internet into thinking that the victim has asked a question – millions of times.

Forging the source address contained within packets is relatively easy to do, and it has been known about for a very long time and the counter-measure has also been known for nearly as long. To put it simply, all the ISP has to do is to not allow packets to exit their network(s) which contain a source address that does not belong to them. Yet many ISPs – the so-called “bad” ISPs – do not implement this essential bit of basic security. The excuse that implementing such filters would be impossible with their current routers simply doesn’t wash – routers that will do this easily have been on the market for many years.

It is laziness pure and simple.

These bad ISPs need to be discovered, named, and shamed.