The upcoming Black Hat security conference in Las Vegas offers an annual parade of security researchers revealing new ways to break various elements of the Internet. But few of the talks have titles quite as alarming as one on this year's schedule: "How to Hack Millions of Routers."

Craig Heffner, a researcher with Maryland-based security consultancy Seismic, plans to release a software tool at the conference later this month that he says could be used on about half the existing models of home routers, including most Linksys, Dell, and Verizon Fios or DSL versions. Users who connect to the Internet through those devices and are tricked into visiting a page that an attacker has set up with Heffner's exploit could have their router hijacked and used to steal information or redirect the user's browsing.

Heffner's attack is a variation on a technique known as "DNS rebinding," a trick that's been discussed for close to 15 years. "There have been plenty of patches over the years, but this still hasn't really been fixed," he says.

The hack exploits an element of the Domain Name System, or DNS, the Internet's method of converting Web page names into IP address numbers. (When you visit, for instance, a domain name server might convert that name into the IP address Modern browsers have safeguards that prevent sites from accessing any information that's not at their registered IP address.

But a site can have multiple IP addresses, a flexibility in the system designed to let sites balance traffic among multiple servers or provide backup options.

Heffner's trick is to create a site that lists a visitor's own IP address as one of those options. When a visitor comes to his booby-trapped site, a script runs that switches to its alternate IP address--in reality the user's own IP address--and accesses the visitor's home network, potentially hijacking their browser and gaining access to their router settings.

That DNS trick isn't new, and browsers have installed patches for earlier versions of the exploit. But Heffner says he's tweaked it to bypass those safeguards; He won't say exactly how until his Black Hat talk. "The way that [those patches] are circumvented is actually fairly well known," says Heffner. "It just hasn't been put together like this before."

Heffner tested his attack against 30 router models and found that about half were vulnerable.

Potential fixes implemented in the free DNS replacement OpenDNS and the Firefox NoScript plug-in won't prevent his exploit, Heffner adds.

One comfort for users may be that Heffner's method still requires the attacker to compromise the victim's router after gaining access to his or her network. But that can be accomplished by using a vulnerability in the device's software or by simply trying the default login password. Only a tiny fraction of users actually change their router's login settings, says Heffner. "Routers are usually poorly configured and have vulnerabilities," he says. "So the trick isn't how to exploit the router. It's how to get access to it."

That means concerned users should make sure their router's firmware is updated and patched, and that they're not using default security settings.

Heffner, like most security researchers revealing dangerous bugs, argues that releasing an exploit may be the most effective way to draw attention to severity of the problem and convince both browser and router makers to fix the fundamental vulnerability. "Iím not the first to give a Black Hat talk on DNS rebinding, and I wonít be last," he says. "Everyone has had ample time to fix this."

Source: Ars Technica