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DNS Vulnerability

by @ 10:42 pm
Filed under: computers,hacking

While programming is my main focus at my company, one of my side jobs at work is networking. I have no complaints as I'm curious and interested in the inner workings of computer networks. Our IT department handles most of the networking tasks, but I usually find myself getting involved in setting up connectivity in the company. Whether it's a firewall, a router, a reverse proxy, or a DNS server, I find the networking field too fascinating to ignore.

That's why when the latest DNS vulnerability, discovered by Dan Kaminsky, came to light in April 2008, I began investigating our DNS servers to determine the risk factors. Dan's site contains a simple tool to assess the risk and it identified all of our caching DNS servers as vulnerable. A patch from Microsoft took care of our Windows-based DNS servers, but there was also a Fedora server in the mix running an old version of BIND that needed attention. Patching that server would have required upgrading to a newer version of Fedora.

I knew I could buy some time using the safety-in-numbers logic, but today I finally decided to tackle that server and plug the hole. My intention was to install the newest version of Fedora (version 9) on a new hardware and then add a patched version of BIND on top. BIND is a great name server product but it has a large footprint that seems like an overkill as a caching server. There are several other free DNS products out there so I began to look for an alternative.

My search eventually led me to PowerDNS (PDNS) and I decided to give that product a try. After installing Fedora 9 on the server, I downloaded the latest RPM of PNDS and promptly installed it on the server. PDNS comes in two flavors. The authoritative version and the caching version, known as Recursor which is the one I was interested in. The install was a breeze and the configuration was as easy as importing some of the data from the old BIND server and making some quick edits to the recursor.conf file. A server restart to make sure everything is in order, and I had the new caching server up and running, resolving names.

PDNS has been free of the DNS cache poisoning vulnerability for a few years now, and Dan's site confirmed that the new server was indeed running at much safer levels.

There is little doubt that the bad guys are hard at work to poison as many DNS servers as they can get their hands on. If your unpatched servers haven't been targeted yet, it's only a matter of time before they are. Whatever method or product you use to avert this risk, the sooner you do it, the better. As a quick alternative, you can use one of several free and already safe services like the one offered by OpenDNS.com as direct name servers or as forwarders on your caching servers.

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