Decoding the DNS: A new arena in cyber defence

Cyber defence tactics are constantly evolving to meet new threats - but one area that has been undervalued up until now is the Domain Name System (DNS), says Simon McCalla.

Simon McCalla, CTO of Nominet
Simon McCalla, CTO of Nominet

Any company with a large DNS infrastructure will find it difficult to understand what is happening. This is down to the sheer volume of data involved – you could be looking for patterns in millions if not billions of requests to and around your network.

However, new tools are emerging which capitalise on advanced big data techniques to analyse DNS data in depth, opening up the possibilities for using DNS data as an intelligence gathering mechanism in the war against cyber-crime.

Before now, the insights that can be found amongst the four billion DNS queries that the .UK zone receives on a daily basis have largely been hidden because tools capable of analysing traffic across periods of more than a few minutes didn't exist. But with new DNS analytics and visualisation tools that have the capacity to store and analyse DNS queries data in-depth, we've begun to uncover techniques for identifying patterns of use that indicate malicious activity or cyber security vulnerabilities. Here are two:

Identifying botnets and spam

One example of cyber intelligence that can be gained from DNS analysis relates to botnets. Botnets continue to contribute to DDoS attacks and spam runs. Recent research from Kaspersky found that over 23,000 botnet-assisted DDoS attacks were reported in Q1 of this year alone. Spam email also continues to cause problems – despite recently dropping to a 12 year low spam still represents almost half of all emails sent.

DNS data can reveal previously hidden tell-tale signs that computers on your network have become part of a botnet. A typical spam run centres on mass mailing to a list which almost inevitably will contain many invalid or expired domains. DNS analysis can reveal abnormally large numbers of requests for domains that do not exist, suggesting that machines on the network have been compromised.

By recognising specific infections early, it's possible to quickly clean up or at least isolate the infected machines and reduce the amount of spam crossing your network. The bigger your infrastructure, the more helpful such techniques are.

Limiting the spread of malware

The fight against malware is another area which can be assisted by DNS analysis. When it comes to Malware Index Case detection, DNS analysis has enabled the identification of a particularly aggressive piece of malware by tracking infected machines which were using something called a Domain Generation Algorithm (DGA), an algorithm that generates a number of random domains for botnets to communicate with.

DGA works by using an algorithm that generates a number of domains that changes periodically, and is often spread over many jurisdictions which means it is hard to predict. This allows the cyber-criminal to communicate with a large army of machines but reduces the risk of a white-hat adversary taking back control, as instead of having a single point of vulnerability, the cyber-criminal has many domains to hide behind.

DGAs are used by many pieces of malware, and tend to have two characteristics: They look like random strings and are in use for only a fixed period of time, commonly 24 hours. This means that a machine on your network that's trying to resolve a set of domains which don't look like humanly readable words i.e., may well be an infected machine.

If the set of domains changes on a daily basis, then this is even stronger evidence. By analysing DNS data, security professionals can find, predict and sinkhole the traffic of most DGAs by looking into a company's recursive DNS traffic.

 With cyber-criminals constantly finding new and intelligent ways in which to infiltrate a company's network, the ability to analyse DNS data opens up a whole new avenue of protection for organisations.

Decoding the DNS gives businesses another tool in their arsenal, one which was previously significantly more limited than it is now. If your organisation has a large DNS infrastructure but you haven't previously been able to extract meaningful intelligence from DNS data, now may be the time to consider reassessing your options.

Contributed by Simon McCalla, the CTO of Nominet – the private, not-for-profit business, responsible for the smooth and secure running of the .UK internet infrastructure.