Criminals hack 300,000 home routers as part of mystery 'pharming' attack

DNS redirection is latest in growing number of attacks

Criminals have quietly compromised 300,000 consumer and small office routers as part of a newly-discovered global DNS redirection campaign, independent US research outfit Team Cymru has discovered.

Uncovered in January but dating back to at least December, the 'pharming' attack redirects DNS queries via new IP addresses, in effect setting up a silent man-in-the-middle that gives the criminals complete control over which sites the user can visit.

It's like an advanced form of phishing except that victim does not have to make the mistake of visiting the wrong website; the DNS redirection does that for the attacker.

According to Team Cymru, a wide range of routers appear to be vulnerable (depending on the firmware used), including D-Link, TP-Link, Micronet and Tenda. The overwhelming majority of hijacked routers appear to be in Vietnam but smaller numbers were also detected in Italy, Thailand, Colombia, the Ukraine, Bosnia and Herzegovina, and Serbia.

The 300,000 victim total derived from the number of IP addresses contacting the two IP DNS servers used in the redirection in a one-week period, Team Cymru said.

Given that routers did not appear to be using default passwords, how the attackers gained control is a worry. The routers in question all had documented security weaknesses, including authentication bypass and deadly Cross-Site Request Forgery (CSRF) exploits.

Team Cymru noted the similarities in modus operandi to another recent router DNS redirection online bank hijack (publicised by the Polish Computer Emergency Response Team) last month. That was designed to attack online bank website sessions, probably the purpose of the new attack.

"While these attacks both altered the DNS server IP addresses used by victim routers, subtle differences in the tradecraft employed makes it likely that we are observing either separate campaigns by the same group, or multiple actors utilizing the same technique for different purposes," said Team Cymru's analysis.

The latest revelation is more evidence that criminals are turning their attention to home and SME routers as a new soft target. Unlike attacks on PCs, they are considerably harder to detect and users would be unlikely to notice DNS redirection until it was too late.

Coincidentally, a recent Tripwire study found that many popular routers sold on Amazon - the class of device hacked for the latest attack - are vulnerable to compromise. Poor configuration has played a part in this but so too has insecure software design and patching by vendors.

Last year, a separate analysis by Independent Security Evaluators reported much the same thing - many popular home and SOHO routers are wide open to exploitation by hackers aware of their weaknesses. It's also a fact that CSRF attacks on routers have been a worry for years and yet these attacks remain surprisingly easy to pull off against this class of router.

Last month, SANS researchers reported that 'TheMoon' worm was targeting Linksys routers running certain firmware versions. The home router is starting to look like a new cybercrime's perfect back door.

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