NSA's whitelisting approach economically blocks computer viruses

Military computers soon will be configured to execute only administrator-approved software applications in certain areas of a computer, Pentagon officials told Nextgov. The Defense Department's unique version of the "application whitelisting" approach focuses on where downloads are allowed to launch in a system. It is intended to be a relatively inexpensive protection against downloads that antivirus programs fail to flag as threats.

"You can download it, but you can't install it," said Paul Bartock, a technical director for the Information Assurance Directorate at the Pentagon's National Security Agency, who helped develop the economical technique.

One weakness with even the best antivirus programs is they blacklist software only after it has been diagnosed as malicious. Unknown worms can't be blocked. And hackers continuously tweak their code so it remains unknown.

However, NSA's approach in essence blocks every application from executing until a network administrator has approved, or whitelisted, it. Whitelisting is a recommended best practice, but Defense and industry have lagged in adoption because of the staffing involved in adding and removing applications from the list, NSA officials said.

To save time, NSA created a way to grant applications access based on where they are trying to open in a system -- for example, certain disk drives or directories. With typical whitelisting, an administrator has to change the list every time a developer releases a new patch or program update. Under NSA's approach, administrators are able to focus their attention on fewer potential entry points for viruses, thus reducing the time involved in installing new applications.

Now, NSA is arranging for the baseline configurations of all new Defense computers to employ the tactic, said Eric Chudow, who works with Bartock in the directorate.

This method already has thwarted one type of worm that antivirus programs failed to catch. Chudow explained: "An email tried to install malware. On the newer baseline computers, the administrators could see this was malware," but on the older models, "the antivirus wasn't able to protect against it yet. Two weeks later, the antivirus vendors issued a signature for that particular piece of malware."

Commercial whitelisting software can cost hundreds of thousands of dollars and require three full-time employees to change the list for every patch and upgrade. NSA officials were able to do the job without licensing special software. They used software-restriction features that come with most operating systems, along with an existing intrusion detection system, and then wrote some special permissions, officials said.

The project required monitoring the agency's network about 20 hours a week for three months to make sure the new configuration was not obstructing important applications, officials added. For ongoing upkeep, only an hour of attention per week is required.

Almost anyone, including home computer users and health technicians, can try the technique, Bartock said.

The procedures are largely invisible to computer users, unless for example, a soldier tries to launch a file-sharing tool. "It's actually pretty negligible interference, as long as the end users aren't using any applications that they aren't supposed to," Chudow said.