1. Life & Code
(The title of this section is taken from Johnny’s blog of the same name, Life and Code. Although my implementation of the phrase isn’t in terms with Johnny’s, yet I could resist using it. 🙂 )
Life: Three days ago I found that there are some strange entries in my local Apache web server logs. Something like:
127.0.0.1 - - [18/Dec/2007:19:39:26 +0530] "GET /iview/msnnkhac001160x600Xdig1600000185msn/direct;wi.160;hi.600/01 HTTP/1.1" 404 352
127.0.0.1 - - [18/Dec/2007:19:42:19 +0530] "GET /pagead/show_ads.js HTTP/1.1" 404 320
Code: Bitdefender informs of a malware, termed as Trojan.Qhost.WU, is redirecting all the requests made to the Google’s ad server (page2.googlesyndication.com) by the victims browser to a rougue ad server.
2. Impact of the issue:
Reportedly, a big part of Google’s earnings comes from it’s Ad services. Thus this trojan is not only depriving Google of it’s earning’s, but also the publishers who work hard and hope to make some quick buck for their evening coffee.
3. The enigmatic “hosts” file:
You all know that every system connected directly to the internet is assigned a unique IP address. The domain name (viz. http://projectbee.org) is nothing but a unique name assigned to a unique IP (although more than one domain name can be mapped to an ip address, that is not our concern right now). This mapping is stored in DNS servers. Each time the browser tries to open up a site, a nearby DNS server is queried to find the ip address.
However, before all this, the DNS server of your local system, hosts file, is queried. (Don’t mistake me, this DNS server is just a metaphor 🙂 ). The hosts file stores a domain name to ip address mapping for domains that don’t need a query to DNS server. e.g., localhost is mapped to 127.0.0.1, the loopback ip, i.e. the ip of local system.
On your windows 2000/NT onwards system, it’s located at %systemroot%\system32\drivers\etc\hosts and on your *nix systems at /etc/hosts. More info on location can be found here.
Now coming back to my problem; unable to find any satisfactory answer, I posted it on Slackers. (Giorgio) Maone, better known as author of the awesome NoScript plugin for Fx, immediately responded, and asked me to check my hosts file.
I had added a number of entries of ad serving sites to point to the local ip in my hosts file and forgotten. I did this to prevent ads from being loaded. Hence, each time any of these sites were called, the hosts file redirected the requests to my local server.
So pretty obviously, I was/am not infected.
“Why do you post the junk about your issue then?”, you ask.
“Because it was a strange coincidence, and because I can, honey :P”
4. How the exploit works?
It’s fairly simple, the malware modifies your hosts file and adds an entry for page2.googlesyndication.com to prevent DNS lookups and direct all the requests to the malicious server.
5. How do I protect myself?
1. Locate your hosts file and remove any entry for page2.googlesyndication.com. Alternately, you can even modify the entry to point to your local ip, in case you don’t wish to see those ads.
2. Let your Antivirus/AntiSpyware do it for you.
What! Dump M$ Windows for Linux. 😛
Seriously, “Linux ain’t easy to use” is a myth. Moreover, if you are into flashy looks, try compiz-beryl package. It IS Awesome… (and consumes amazingly less resources than…uh Vista.)
7. Bonus Tip
In case you wish to prevent your kids, partner, (or even parents) from visiting some sites; or do not wish to see those crappy ads from being loaded, you might consider editing your hosts file. For more information or even sample hosts files, use Yahoo! search.