Rogue DNS Attacks – A less understood hacker attack

The title of this article originally included “…and why you could lose your internet this July”, but that was in Feb. 2012 when I started writing this before that life got in the way.  I’ve left the part about losing your internet but edited it to be more relevant to today.  See the section on “Operation Ghost Click” at the bottom.  These types of attacks are a little better understood these days, but still unknown to much of the public.

The Rogue DNS Attack, a.k.a. “DNS Hijacking” is one of the more misunderstood types of attacks that can open the door for hackers to use all kinds of trickery to steal information you store on or transmit from your computer, like the embarrassing video you took of yourself singing and dancing to MC Hammer wearing your Dad’s very large pants and forgot to delete.  Oh yeah and any password you type into any website.  Even your dog.

What’s that?  You don’t have a dog?  Actually you did… until they stole it.  I guess they also stole your memory of your dog.



To understand them, you first need at least a basic understanding of how DNS servers work.  The short version is that any time you type a website’s name into your browser (, to use an example everyone is thoroughly familiar with.), or click a link, etc. your computer first sends the domain name to a DNS server, which responds with the IP address(es) needed to actually reach the server where the website is hosted.

For a more detailed explanation of how the devices in your network fit together, see my previous post, How Does Your Computer Connect To The Internet?



So in addition to the legit DNS servers you know and love (obviously), there are “evil” DNS servers in the world that would love for you to use their “services” instead.  If your DNS settings were somehow changed to point to one of these Rogue DNS Servers, you’d be in a lot of trouble.  In fact, there’s a possibility you are already pointing to one now and didn’t even know it!  But more on that later.



We’ll start with the symptoms since knowing how to spot it is usually the most important piece.  First, you may notice your browser behaving strangely.  There are a few scenarios that could be involved, some of which may cause noticeable changes in behavior.

Scenario 1: When you open a browser (any browser), and try to go to a website, some other unexpected page comes up.



  • Often this page will claim it has detected spyware or a virus and that you must download some tool to remove it.  Don’t ever download a virus removal tool advertised in this manner.  The “tool” most likely is actually a virus or maybe in rare cases a red herring to distract you from some other attack.
  • Sometimes there is a legitimate reason for the redirect… for example, some public wireless services require you to agree to their terms or authenticate on some local page before they let you get out to the public DNS.  This is (usually) not an attack, but does behave much like one.



Scenario 2: When you are opening webpages you start noticing that although the webpage you requested is opening, the status bar at the bottom of your browser window is telling you it’s requesting data from some website you’ve never heard before and it happens over and over again regardless of what website you browse to.  But you may eventually get to the site you wanted, so it may seem like nothing is wrong.

There is also a third scenario that may not be noticeable at all:

Scenario 3:  Sometimes you will get a certificate error from a site you have visited before.  There are reasons for a certificate error that are less dangerous (company let their certificate expire or your clock somehow got reset to Jan 1, 1970 and the browser wrongly thinks the certificate expired).  Because of this, or because maybe you have to make a bank transaction NOW or update your facebook status NOW people assume it’s not worth investigating and elect to go to the site anyway, or worse, permanently accept the bad certificate.  If you’ve done this, or the attacker really knows what they’re doing, there may even be no noticeable symptoms at all!



I’m glad you asked!  You really do ask good questions.  The first of the scenarios listed above is bad for obvious reasons: it prevents you from accessing the internet, essentially making machines useless for the average user.  But then you just call up a computer repair service. Or like my family does with me, call your computer programmer friend/relative because you think the Geek Squad prices are too high, which is like asking your accountant to do your bookkeeping for you for free even though bookkeeping isn’t really his thing… What were we talking about again?  Oh yeah…

The second and third scenarios are WORSE.  Most users don’t notice anything wrong and continue to browse the web, not realizing that you are being redirected to a fake website posing as the real one (Scenario 2) or pointing to a proxy server which can act like ANY website you requested.  For now, don’t worry about what a proxy server is, just know that there are good ones and bad ones.  And in this case, the proxy server can see everything you input and can see and manipulate the responses you are getting from the requested site.  Attacks like this are known as:



Here’s how a MITM attack works.  Using as an example, you browse to   In the case of a Rogue DNS attack, our computer does it’s DNS request and gets the IP address of a malicious proxy server instead of the real

The proxy server then browses to behind the scenes, pretending to be you, gets the resulting page and forwards it on to you as though it were the real webpage.  It basically pretends to be  This by itself wouldn’t be such a problem (maybe slow your browsing down a bit), except now you think you are pointing to the real and are likely to enter your username and password, which the proxy server is logging so the owners now have your password and possibly everything you saw while you were on the site.

Not only that, but the proxy server, before forwarding the results to you, can also modify these results however they want before sending them back.  For example, if you search for “how to remove a virus”, maybe there are a few known sites that show you how to remove it and it can hide those links from you so you will have a tougher time finding them.  They can also take a file you are downloading (like a bank statement) and replace it with a virus, or inject malicious code into the PDF, etc.  They can even inject malicious javascript into the webpage that your computer will run.  Hope your browser is up to date!

Or put more simply, once you’re pointing to one of these bad proxy servers, there’s an endless number of tricks they could use to steal your identity and remain undetected.

Since your browser thinks you’re talking directly to Google, which you might have listed as a trusted site, it executes the malicious code.  Or even worse, you log into your web-based email site (gmail, ymail, hotmail, etc.) and your browser tells you the certificate provided by the site is invalid, but because you need to get to your email now (or just don’t know any better), you accept the invalid certificate.  Now the malicious site can act as a SECURE intermediary between you and your site, which means they can see your username, password and everything else you input or view on that site even if the site is “secure”, a.k.a. encrypted with an SSL certificate.




There is no way to confirm for sure, because hackers will always try to find ways to outsmart any standard method for protecting against anything.  But for most cases you can do the following:

First, find out which DNS server(s) you are using.



Click  Start > Run  (or if there is no “Run” option, click “Search programs and files”)

Type the following command and press ENTER:


This will open up a “Command Prompt” window.  Type the following and hit ENTER to see your network settings:

ipconfig /all

Find your network adapter and look for the line that says “DNS Servers”


Linux (and probably Mac – I don’t have one to test with):

Open a terminal window if you aren’t already at a shell prompt, type the following and press ENTER:

cat /etc/resolv.conf


Now it can be tough to know if a DNS server is bad just from the IP address.  But if you happen to know what your DNS server was originally and it has changed, this is a bad sign.

If you don’t know what DNS server you should be using, you can try looking up the IP address using the nslookup command (Windows) or host command (Linux – if nslookup not available).


Use a small website, because huge sites like Google, Twitter, Facebook, etc. do complex tricky stuff to handle their massive loads, so doing an nslookup may give you 15 results and those results may change every so often.

Generally when you run this command it will first tell you the DNS server it used, followed by the IP Address(es) of the domain you entered (in this case,

Then, run the command again, except force it to use a known public DNS server.  I generally use the Google public DNS ( or, but it’s a good idea to pick your own from a database of known DNS servers.


Did you get the same results?  If not, chances are the DNS server you were using is bogus.



There are a number of ways this can happen.  Here are the usual suspects:

Attack 1: HACKING YOUR MACHINE – Someone hacked into your computer and changed your settings.  Probably the least common method, unless you make it a habit to piss off hackers.  (Pro tip: don’t be mean to hackers.  They tend not to be forgetful.)

Attack 2: MALWARE – Someone tricked you into running a malicious application and now you have a virus that is hiding behind the scenes and changing your DNS settings to point to this bad server.  Example: DNSChanger

Attack 3: HACKING YOUR NETWORK HARDWARE – Someone hacked into the DHCP server on the network to which you are connected.  They changed the settings of your previously legitimate DHCP server to point to a Rogue DNS Server.  Now the router is broadcasting the rogue DNS server to all machines that connect to it.

Attack 4: ROGUE DHCP SERVER – This is an even more sneaky attack than the above three.  A Rogue DHCP Server does the same thing as your legitimate DHCP server.  Now any new machine that connects to your network will issue a DHCP request as usual to get an IP address and DNS servers, etc., but instead of the usual single response from your legit DHCP server, suddenly there are two responses being sent.  If your machine picks up the bad DHCP response instead of the legit one, it will blindly start using the Rogue DNS server instead of the good one that your ISP recommended.

The first 2 methods can often be prevented using standard best practices for keeping your computer secure like using strong passwords, keeping your software updated, not executing files or clicking links in suspicious emails, etc.



If you are already a victim of this attack, fixing it depends on how you were attacked.

If it was a one-time hack that caused it, and no malware was involved, rebooting your machine, reconnecting to the network or forcing a DHCP request will fix your issue.  Now you just need to make sure you update all your software and passwords so you don’t get hacked again.

If you have malware, this is a more general problem beyond the scope of this article, but the first thing to do if at all possible is IMMEDIATELY DISCONNECT the computer from the internet and do not reconnect it until you have removed the malware. If possible, use another machine for any needed research, downloads, etc.  Most malware is designed to be tricky to clean, so if you don’t have a backup image or can’t restore your machine to factory defaults, you may have to call Geek Squad or your local computer repair place for help.  Or you can try some of the how-to videos on youtube.  Here’s one example.

My next article will get into how attack 4 can happen, and what to do if it happens to you.  I will also detail my experience with a Rogue DHCP Server attack in my office.



A couple extra things I pulled out of the above article because it was getting too long:


I included this because I saw a lot of people posting things in forums where they were going to Google and the search results were redirecting them to bad websites.  Often people were responding saying it’s the “Google Redirect Virus”.  There is an actual virus known as the “Google Redirect Virus”, which is a type of browser hijacking virus.  I even recall some discussions about how this is because Google was hacked, etc.

First off, the number one site on the internet is Google.  Since most people use search engines to find practically all information on the internet that’s not from a social networking site, Google tends to be the most common page many users look at.  There are some people that call this issue the “Google Redirect Virus”.  This is because they notice funny behavior while they are clicking links in their Google search results.  But as you will see the problem has absolutely nothing to do with Google, except for the fact that it is programmed to only spring into action when you use Google.  The same thing could be done for any other site on the web.


The biggest example of this is an Estonian ring of cybercriminals taken down by the FBI in Nov. 2011 in an investigation dubbed Operation Ghost Click.  (witty, huh?)  This ring used a computer virus to infect millions of computers and trick them into pointing to their Rogue DNS Servers.  The FBI seized a large network of these servers, but since shutting them all down would “break the internet” for millions of victims, they replaced the bad servers with legitimate ones, and they referred the public to a webpage that helps you identify if you’re using one of them.

In fact, there was a period of time in early 2012 where the FBI was no longer able to maintain the Legit DNS Servers that replaced the bad ones, and they were planning to shut them all down.  many were worried that all of the remaining victims would lose internet access.  See the CNBC article titled: FBI: Hundreds of Thousands May Lose Internet in July

I wasn’t worried that this would be a major issue, because who do you blame when the internet stops working?  Your evil ISP whose customer service notoriously drives people crazy.  And those ISP’s don’t like outages, even if they’re not really at fault.  So I’m sure their networking geniuses came up with a way of rerouting traffic to known FBI DNS servers back to a legitimate one so that even victims who were still affected would maybe get a warning page or just redirected as if nothing were wrong.

But does this mean Rogue DNS Servers are no longer a problem?  Very doubtful.  There will probably be new ones popping up all over the place.  Ones not among those seized by the FBI.  So even if you aren’t pointing to one of the DNS servers seized by the FBI, you could still be pointing to a Rogue DNS Server.  In fact, when someone at my company had this problem the link above did not detect it.