Monday, December 15, 2008

Watch Out For The DNSChanger Trojan Horse; It Redirects The First Page Of All Google Or Yahoo Web Searches To False URLs

There's a trojan horse making the rounds that affects the first page of any Google or Yahoo web search (I did not test it on any others). It matches the description of the DNSChanger Trojan Horse, further described in an article published by There's also a Mac equivalent, called OSX.RSPlug.A Trojan Horse. This Trojan Horse has been around for a while.

Here's how I discovered it. I clicked on a picture of a scantily-clad woman in a Google image search, then copied the image URL and posted it to another website. All of a sudden, I was getting strange results on Google web searches. For example, when I typed Voice Of Deseret, this blog came up first on the first page like it always does, but the URL was for a different site. I noticed the same results for every other site listed on the first page. The redirect URLs were for a given series of commercial sites. However, the second and subsequent Google pages were unaffected.

This phenomena happened regardless of whatever search term I typed in. It appears whoever operated the site from where I got the girl's picture wrote a script which changes your DNS settings and falsely redirects your search to the set of commercial sites they are interested in promoting. It is not known whether it's deliberate or accidental; other references I reviewed implied that a person attempting to innocently boost a website in the SEO rankings could inadvertently create this effect.

Norton and Bit Defender could not get rid of the problem; their searches for viruses and malware came up negative. Finally, I exercised the "nuclear option" and deployed the System Recovery CD which came with my Gateway laptop. This deleted all the files on my laptop, re-formatted the hard drive, and installed the original "factory" files. The recovery was successful and the trojan horse is gone.

However, you may not need to go that far. According to TheRegister article, a less drastic solution is to hard-code your DNS entries in your computer's network configuration settings. Here's the article:

Researchers have identified a new trojan that can tamper with a wide array of devices on a local network, an exploit that sends them to impostor websites even if they are hardened machines that are fully patched or run non-Windows operating systems.

The malware is a new variant of the DNSChanger, a trojan that has long been known to change the domain name system settings of PCs and Macs alike. According to researchers with anti-virus provider McAfee's Avert Labs, the update allows a single infected machine to pollute the DNS settings of potentially hundreds of other devices running on the same local area network by undermining its dynamic host configuration protocol, or DHCP, which dynamically allocates IP addresses.

"Systems that are not infected with the malware can still have the payload of communicating with the rogue DNS servers delivered to them," McAfee's Craig Schmugar writes here of the new variant. "This is achieved without exploiting any security vulnerability."

The scenario plays out something like this:

-- Jill connects a PC infected by the new DNSChanger variant to a coffee shop's WiFi hotspot or her employer's local network.
-- Steve connects to the same network using a fully-patched Linux box, which requests an IP address.
-- Jill's PC injects a DHCP offer command to instruct Steve's computer to rout all DNS requests through a booby-trapped DNS server.
-- Steve's Linux box can no longer be trusted to visit authoritative websites. Although the address bar on his browser may show he is accessing, he may in fact be at an impostor website.
-- The only way a user might know the attack is underway is by manually checking the DNS server his computer is using (e.g. by typing "ipconfig /all" at a Windows command prompt). There are several countermeasures users can take, Schmugar said, the easiest being hard-coding a DNS server in a machine's configuration settings.

(In Windows, this can be done by going to Start > Control Panel > Network Connections and right clicking on Local Area Connection and choosing properties. Scroll down to Internet Protocol (TCP/IP) and click the Properties button. Then type in the primary and secondary for your DNS service. We're partial to OpenDNS, whose settings are and

In an interview, Schmugar said the DHCP attack doesn't exploit a vulnerability in either user machines or network hardware, allowing it to work with a wide variety of home and enterprise routers. It involves a ndisprot.sys driver that is installed on the infected box. Once there, it monitors network traffic for DHCP requests and responds with bogus offers that contain the IP address to the rogue DNS server.

This problem is different than the virus currently affecting Facebook sites. I have now discovered that Symantec picked up on it earlier and has posted some information HERE. Symantec refers to it as "Trojan.Flush.K".


bekkieann said...

Are you running any anti-spyware like Spybot Search and Control or AdAware? These are both free and often fill in the gaps missed by Norton, McAfee and others. I'm curious to know if these did not find this trojan.

Deseret Dawg said...

No, I'm not running the anti-spyware software you specified. But I did find out after the fact that Symantec did address this issue in greater detail HERE. Still doesn't explain why Norton 360 didn't detect it, unless this trojan horse is a newer variant.

Actually, reloading Windows XP was probably not a bad thing. It's probably good to scrub down and reformat the hard drive once in a while. Purges all the stray crap.

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