Your DNS Server Is Helping DDoS Attacks

Andrew Froehlich, Network Engineer & IT Consultant | 5/1/2013 | 13 comments

Andrew Froehlich
In the first quarter of this year, it was reported that the Internet experienced a 700 percent DDoS bandwidth increase. As DDoS attacks force more bandwidth onto a target, it means that even the largest enterprise networks can succumb to over-utilization.

DDoS attacks are growing increasingly sophisticated and take advantage of dozens, hundreds, or even thousands of compromised machines that form enormous botnets. But more importantly, they increasingly make use of non-compromised, but misconfigured, public DNS servers. Your enterprise might be responsible for these servers.

Public DNS servers are most commonly owned and operated by Internet service providers (ISPs) or major Internet companies such as Google. But enterprise organizations that support multiple datacenters often find it valuable to run their own public DNS. There are a number of benefits to running your own public DNS server. For example, with a locally managed DNS server, you're able to set TTLs; flush updates; build multi-site, high-availability configurations; and make other parameter adjustments.

But running a public DNS server also comes with added responsibilities. First of all, it must be designed to be highly reliable. If a public DNS server malfunctions, lots of people are going to notice. Additionally, there is a growing problem of being both a DDoS target and an oblivious accomplice in attacks. There's not too much you can do about being targeted, but there are steps that can be made to prevent you from inadvertently assisting in an attack.

A single DNS query is a very low-bandwidth transaction. A DNS server can handle thousands of DNS requests every second and the amount of bandwidth consumed per request is typically under 512 bytes. Bandwidth ramps up with zone transfer files. Zone files contain domain name to IP address mappings for an entire domain. Depending on the size of that domain, the files can get very large. Recent DDoS attacks have taken advantage of the fact that many public DNS resolvers do not verify the source IP address for DNS requests.

Because of that, DDoS bots can request zone transfer files from thousands of DNS servers at once, giving a source IP address of the site that is under attack. The misconfigured DNS servers then send the zone files back to the target network, often overwhelming the target's Internet bandwidth and knocking the site offline.

If your company manages a public DNS server, you may be under the false impression that it is properly set up and secured. But you may be surprised to find that the vast majority of public DNS servers are vulnerable to spoofs or other DDoS exploits. The Open DNS Resolver Project claims that they have scoured the Internet and have identified over 27 million open DNS servers. And of those, over 25 million "pose a significant threat." That number is frightening and needs to be lowered considerably until it becomes too difficult for hackers to find open DNS servers to exploit.

So please, do your fellow Internet neighbors a favor and ensure your DNS settings are properly set. This is one way we can take a tool away from a hacker's growing toolset. Given the increasing threats from DDOS attacks to the financial industry, it may be the entire economy you are protecting.

View Comments: Newest First | Oldest First | Threaded View
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Susan Nunziata   Your DNS Server Is Helping DDoS Attacks   5/31/2013 7:55:15 PM
Re: over 25 million "pose a significant threat."
@Damian: Even regulations wouldn't solve the problem, because by the time the regulations were enacted the technology would have progressed so far as to make the regulations obsolete.

Perhaps there needs to be a sort of vigitlante enterprise security group formed across enterprises and across vertical markets to take matters into our own hands. 
Damian Romano   Your DNS Server Is Helping DDoS Attacks   5/31/2013 5:47:54 AM
Re: over 25 million "pose a significant threat."
@susan - And with more and more being put online and the more technologies being released, that only produces more criminal activity and hence, the increased need for security awareness. 
Susan Nunziata   Your DNS Server Is Helping DDoS Attacks   5/29/2013 3:33:23 PM
Re: over 25 million "pose a significant threat."
@Damian: it is truly scary and unfortunate that businesses take this mindset about security, even as they're increasingly moving their operations online and into the cloud. Given that there have been some pretty major breaches already, I do wonder what it will finally take to convince organizations of the importance of investing in security, and looking for weaknesses like the ones pointed out in this article. Yikes!
Damian Romano   Your DNS Server Is Helping DDoS Attacks   5/29/2013 2:40:50 AM
Re: over 25 million "pose a significant threat."
@Susan - I wish I had the answer to that question. Security is always going to be something viewed as not necessary until it's too late. Security is money. And in the eyes of many, money wasted because it oftentimes can't be measured via ROI difinitively. 
Susan Nunziata   Your DNS Server Is Helping DDoS Attacks   5/29/2013 1:03:12 AM
Re: over 25 million "pose a significant threat."
@Damian: What do you think needs to change? How can the discussion of security be approached in terms that make sense to the business decision-makers who control the purse-strings?
Damian Romano   Your DNS Server Is Helping DDoS Attacks   5/29/2013 12:16:09 AM
Re: over 25 million "pose a significant threat."
@Susan - I truly believe most people do in fact think that way, if we pretend the problem isn't real that it will just go away. Otherwise we may have to take responsibility for our actions. The sad part is, the non-action is what they'll really be responsible for in the end. 
Susan Nunziata   Your DNS Server Is Helping DDoS Attacks   5/29/2013 12:07:32 AM
Re: over 25 million "pose a significant threat."
@Damian: that is truly terrifying. Is this a matter of denial influencing decision-makers? The thinking that: If we pretend the problem isn't real, it will just go away?
Susan Nunziata   Your DNS Server Is Helping DDoS Attacks   5/29/2013 12:05:56 AM
Re: over 25 million "pose a significant threat."
@Kerstin: Great question: Now that the information is out, what sort of action plan is being developed to find a solution?

Let's hope there is a quick-response team working on this very question. 
Damian Romano   Your DNS Server Is Helping DDoS Attacks   5/15/2013 2:09:51 AM
Re: over 25 million "pose a significant threat."
@Susan - Security for some odd reason just isn't something anyone really wants to delve into. Most people think that just because they have an anti-virus software that they're completely protected. 
Kerstin Carson   Your DNS Server Is Helping DDoS Attacks   5/4/2013 5:05:33 AM
Re: over 25 million "pose a significant threat."
Susan Nunziata has asked a key question. With internet technology evolving in so many dynamic ways and the threat of hackers well known within the industry (so much so that academia has stepped in to develop training programs focused on internet security), DNS server misconfiguration shouldn't be the problem that the Open DNS Resolver Project cites.

What sort of community, like Open DNS Resolver Project, is being developed to convene, exchange ideas, and lower the number of significant threats of DNS attacks? Now that the information is out, what sort of action plan is being developed to find a solution?
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