Malware increasingly uses DNS as command and control channel to avoid detection, experts say

Most companies are unprepared to deal with the use of DNS as command and control channel for malware, experts said at the RSA Conference

The number of malware threats that receive instructions from attackers through DNS is expected to increase, and most companies are not currently scanning for such activity on their networks, security experts said at the RSA Conference 2012 on Tuesday.

There are many channels that attackers use for communicating with their botnets, ranging from traditional ones like TCP, IRC and HTTP to more unusual ones like Twitter feeds, Facebook walls and even YouTube comments.

Most malware-generated traffic that passes through these channels can be detected and blocked at the network level by firewalls or intrusion prevention systems.

However, that's not the case for DNS (Domain Name System) and attackers are taking advantage of that, said Ed Skoudis, founder of Counter Hack Challenges and SANS fellow, during a presentation on new attack techniques at the conference.

The DNS protocol is normally used for a precise critical function -- the translation of host names into IP addresses and vice-versa. Because of this, DNS traffic doesn't get filtered or inspected by traffic monitoring solutions and is allowed to flow freely through most networks.

As DNS queries gets passed from one DNS server to another until they reach the authoritative servers for the respective domains, network-level IP blocklists are useless at blocking them.

Skoudis has seen malware that receives instructions via DNS responses being involved in two recent large-scale breaches that resulted in the compromise of millions of accounts. He expects more attackers to adopt this stealthy technique in the following months.

The infected computer doesn't even need to have outbound connectivity. As long as it can resolve the host name through a local DNS server that performs recursive lookups on the Internet, it can communicate with attackers, Skoudis said.

Logging all DNS queries that pass through a local server is impractical because it can lead to serious performance issues. However, using a network sniffer to capture samples periodically for analysis can be a solution, Skoudis said.

Network administrators should look for unusually long queries or responses that contain weird names and encoded data, the security expert said. However, attackers might split the responses in smaller chunks.

Identical queries that get repeated every few minutes can also be an indication of DNS command and control activity, because infected computers will periodically check for new commands.

There are tools available such as DNScat that network administrators can use to simulate non-standard DNS traffic and develop detection strategies. Tunneling traffic through DNS servers is not a new technique, but it will likely increasingly appeal to cybercriminals who are looking for ways to avoid detection, especially on corporate networks where remaining hidden for as long as possible is critical for them.

Join the newsletter!

Or

Sign up to gain exclusive access to email subscriptions, event invitations, competitions, giveaways, and much more.

Membership is free, and your security and privacy remain protected. View our privacy policy before signing up.

Error: Please check your email address.
Keep up with the latest tech news, reviews and previews by subscribing to the Good Gear Guide newsletter.

Lucian Constantin

IDG News Service
Show Comments

Cool Tech

Toys for Boys

Family Friendly

Stocking Stuffer

Logitech Ultimate Ears Wonderboom Bluetooth Speaker

Learn more >

SmartLens - Clip on Phone Camera Lens Set of 3

Learn more >

Christmas Gift Guide

Click for more ›

Brand Post

Most Popular Reviews

Latest Articles

Resources

PCW Evaluation Team

Maryellen Rose George

Brother PT-P750W

It’s useful for office tasks as well as pragmatic labelling of equipment and storage – just don’t get too excited and label everything in sight!

Cathy Giles

Brother MFC-L8900CDW

The Brother MFC-L8900CDW is an absolute stand out. I struggle to fault it.

Luke Hill

MSI GT75 TITAN

I need power and lots of it. As a Front End Web developer anything less just won’t cut it which is why the MSI GT75 is an outstanding laptop for me. It’s a sleek and futuristic looking, high quality, beast that has a touch of sci-fi flare about it.

Emily Tyson

MSI GE63 Raider

If you’re looking to invest in your next work horse laptop for work or home use, you can’t go wrong with the MSI GE63.

Laura Johnston

MSI GS65 Stealth Thin

If you can afford the price tag, it is well worth the money. It out performs any other laptop I have tried for gaming, and the transportable design and incredible display also make it ideal for work.

Andrew Teoh

Brother MFC-L9570CDW Multifunction Printer

Touch screen visibility and operation was great and easy to navigate. Each menu and sub-menu was in an understandable order and category

Featured Content

Don’t have an account? Sign up here

Don't have an account? Sign up now

Forgot password?