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Using DNS RPZ to Block Malicious DNS Requests

October 2, 2013 at 10:00 am PST

After delivering several presentations at Cisco Live and Cisco Connect this year, I received a few questions regarding DNS Response Policy Zones (RPZ) and how can they be used to block DNS resolution to known malicious hosts and sites. I decided to write this short post to explain what it is and provide several pointers.

DNS RPZ is a technology developed by ISC available since Bind version 9.8. Network administrators can use DNS RPZ to essentially stop malware-infected hosts from reaching their command and control (C&C) servers by blocking DNS resolution to known malicious hosts and sites. This effectively turns a recursive DNS server into a DNS firewall. In fact, many people refer to DNS RPZ as the “DNS Firewall.” Various ISPs are testing and implementing this to provide additional protection to their customers.

Note: DNS RPZ will block DNS resolution, machines connecting to the C&C via IP address will not be blocked.

The following figure provides an overview of how DNS RPZ works.

RPZ-overview1

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“War, what is it good for” as a security metaphor?

I have a thing for metaphors. I wrote my dissertation on them. And they have helped me enormously as a non-engineer working in IT security.

Metaphors are powerful tools (that’s a metaphor, by the way). Literally referring to something as something else enables us to make mental connections between concepts that are not really the same. War and weapons have proven historically useful metaphors. In wartime, everything changes. We look at the situation, our opponents, and even ourselves very differently (I like the image of a noble warrior on the battlefield more than that of a guy who spends most of his day sitting and typing…)

But metaphors also cause trouble, especially when we use them to over-simplify. I am skeptical of “security as war” metaphors, including that of the arms race. The metaphor detracts from the very real threats of cyber- and information warfare. War doesn’t define security any more than war defines firearms. Unless we are specifically talking about threats from nation states (and a few other actors) using information technology as part of armed conflict, we are not talking about war. And this is not what we are usually talking about in information security.

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Hard Lessons about Hacking and Proxy Services

I was disheartened to read about the 22 September arrest of alleged LulzSec/Anonymous member Cody Kretsinger (known by the handle ‘recursion’) by the FBI as a suspect in the SQL injection attacks on multiple Sony websites. Note that I was not sad to see the good guys bust a cybercriminal, but I was sad to see a nice guy I had met and talked to briefly at BlackHat Las Vegas 2011 turn out to be a suspect wanted by the FBI.

Cody Kretsinger, second from right, at BlackHat 2011

One of the things we at Cisco try to do is reach out to those studying infosec and wanting to make a career in security. At BlackHat Cisco had a contest where the winner got a Pwnie Express PWN Phone, effectively a modified Nokia N900 with some pentesting software loaded. A group of guys, volunteers with the show from an IT school, were fascinated by the PWN Phone – possibly because in their circle a couple of them had Nokia N900s, a device relatively unknown in North America but somewhat popular in certain hacking circles due to the fact that its OS is Linux-based and thus can be made to run things like metasploit (like the PWN Phone does).

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What does it take to be PCI Compliant ?

Many people wonder what it takes to be PCI compliant. More importantly, people want to know the difference between PCI, FISMA, DIACAP and STIG. With so much alphabet soup, one has to wonder what it all means, and what is the best way to navigate these waters.

I’m not here to provide you with all the answers, but I can certainly help you to understand where PCI fits into the picture.

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