Posted by Virus Bulletin on Nov 29, 2013
Open DNS resolvers instrumental in many DDoS attacks.
At the Cyber Security Summit in London, Richard Cox, CIO of DNS blacklist provider Spamhaus, called on the UK government to issue fines to those running open DNS resolvers, PC Pro writes.
Open DNS resolvers have become an important tool for those performing DDoS attacks. Attackers send many small DNS requests, crafted so that they will generate a relatively large response, to open resolvers. The source addresses of the requests are forged to be that of the target, which will then see a very large volume of DNS responses sent to its network.
In this way, attackers can generate very large attacks with relatively few resources. There are few organizations that know as well as Spamhaus how big a problem this can be: Spamhaus was the target of a massive DDoS attack earlier this year.
As CloudFlare's John Graham-Cumming pointed out during his VB2013 presentation on open DNS resolvers, this is not the first time that the open nature of Internet servers has been abused to perform attacks. In the late 1990s, open SMTP relays were just as big a problem: they made it possible to send large amounts of spam through someone else's server. Indeed, Spamhaus was originally set up to list the IP addresses of such open relays.
I agree with Cox that something needs to be done about the large number of open DNS resolvers ready to attack the Internet - though whether governments issuing fines is the solution, I am not so sure.
Firstly, the international nature of the Internet means that a handful of governments making something illegal will have little effect on the Internet as a whole. Secondly, I worry that government regulation of DNS servers will be used as a stepping stone for ill-advised proposals such as PIPA and SOPA.
But that doesn't mean nothing can be done. To my best of knowledge, running an open SMTP relay is still legal. Yet very few are doing so, and thanks to the hard work put in by Spamhaus and others in the anti-spam community, those that do so will see very few of the emails they send actually delivered.
Posted on 29 November 2013 by Martijn Grooten