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What DNS Pinning Means to You

Emerging vulnerability is widespread and tough to fix

9:42 AM -- Browsers, by nature, aren’t very secure. They allow traffic to flow freely from the Internet to your machine behind your corporate firewall. That definition alone should scare you.

Browsers allow employees to surf anywhere on the Internet they choose, within any content controls you may have in place. And given the rash of social networking hacks, even the most benign-sounding places on the Internet are turning into proving grounds for Web application hackers.

Anti-DNS pinning (also known as DNS rebinding) allows an attacker to use DNS tricks to contact an IP address other than the one their browser is currently connected to. The browser is supposed to prevent this by binding the host name to a particular IP address, but this protection is easily subverted if the attacker knows his stuff.

This means that once a user visits a malicious site, that site can make that user's browser point to any other IP address -- and, using JavaScript, the attacker can pull the contents of that site.

Of course, attackers on the Internet can connect directly to the sites they are interested in. But that won't work in an intranet environment. DNS rebinding allows attackers to "see" what is behind a firewall, because the user who is connecting to the malicious Website is sitting behind it. The attacker uses the person’s own browser to forcefully view other pages inside a protected network.

Researchers have known about DNS pinning for about a year now, but there has been a ton of research emerging over the last several months, as more people are starting to understand it. Almost every big company is vulnerable to this flaw, and even some tools like Google Desktop have had issues with it.

Some of the recent research proves that people sitting behind proxy servers are particularly in danger of exploitation. Browser makers also have recognized that their protections against DNS pinning are not performing as expected, allowing for exploitation.

There will be a lot more DNS pinning information coming out in the months ahead, but as a security pro, there is not much you can do at this point. All of the attempts to solve this issue have failed so far, but there is much research still to come.

In the meantime, the only tool that has had some measure of success in stopping DNS pinning exploits is a Firefox plugin called LocalRodeo. While not perfect, it limits connections to intranet IP addresses. A better fix will come in time -- but probably no time soon.

— RSnake is a red-blooded lumberjack whose rants can also be found at Ha.ckers and F*the.net. Special to Dark Reading

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