Security researchers have long known about the vulnerabilities of the RFID readers that many buildings use instead of door locks, but facilities managers have been slow to upgrade to more secure systems.
To draw attention to the problem, at next week's Black Hat conference, Accuvant researchers will be releasing an open source piece of hardware that can be used to circumvent these readers.
When these readers first started being used about 20 years ago, no security was built in, said Mark Baseggio, managing principal consultant at Accuvant.
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Today, as many as 80 percent of buildings are vulnerable.
"It became a concern for me because I'm a physical penetration tester, and I kept going to client sites and the client would be completely ignorant of the vulnerabilities in these systems," he said.
The new device -- called the BLEkey -- will be distributed to the first 200 people who stop by Accuvant's recruiting booth at Black Hat. In addition, the company will be publishing the hardware design and source code online, so that anyone can make their own.
Using the device does require some fiddling with an RFID reader, but Baseggio pointed out that many buildings have them set up on unmonitored doors in back alleys.
The attackers just need to open up the reader, push in the BLEkey and two wires, screw it back together, and walk away.
"Then you can sit 20 feet away from the door with your cellphone, watch people's cards as they walk in, or hit a button on your cellphone and open the door and go in," he said. "I could program the device to lock the door behind me for a minute so nobody could follow me."
Baseggio said that he didn't know if attackers were already taking advantage of this vulnerability.
"But it's hard to fathom that this 20-year-plus vulnerability hasn't been exploited yet," he said. "It's widely known among security types."
BLEkey is a hardware device with a system on a chip and built-in Bluetooth that gets installed in the RFID reader. There's also a client application for Linux that can work with an off-the-shelf card writers to generate cloned cards.
"You can also buy your own RFID reader off eBay and connect this device to it, and it will create a skimmer so that you can read people's cards right off their desks or their belts," said Eric Evenchick, embedded systems architect at Gardena, Calif.-based Faraday Future.
According to Baseggio, manufacturers know about the vulnerability, and have more secure technologies available for sale.
"But most of our customers don't know about it," he said.
There's the Open Supervised Device Protocol, an open standard which supports encryption, he said. But the encryption is optional, so customers need to check that the vendor configures the device properly.
There are also proprietary systems, but they typically haven't been fully audited, he said. They might be very secure, but it's hard for customers to know for certain.
Companies that have the vulnerable readers in place can take steps to make them more secure until they're updated, he added.
For example, the card readers have a built-in tamper switch that should set off an alarm when an attacker takes off the cover to hack into the device.
"Typically, not enough physical wiring is installed so that the tamper switch is on," he said. "A business needs to ensure that a tamper switch is on."
Some kind of monitoring system would also help, he said, whether a human guard or a video camera, with records kept about who walks through the door and when.
For particularly sensitive areas, the cards should be kept in RFID sleeves, so that they can't be read right from people's pockets, he added.