Android NFC hack enables travelers to ride US subways for free, researchers say

The researchers who developed the application said transit systems in other US cities could be vulnerable

By Loek Essers, IDG News Service |  Security, Android, NFC

Contactless fare cards in the New Jersey and San Francisco transit systems can be manipulated using an Android application, enabling travelers to reset their card balance and travel for free, researchers demonstrated on Thursday during the EUSecWest security conference in Amsterdam.

An NFC (near field communication) Android smartphone can read the data from a fare card with, for instance 10 rides on it, using the "UltraReset" application, said Corey Benninger and Max Sobell, security researchers at the Intrepidus Group and the application's developers. When travelers have used up their balance they are able to write the stored data back to the card using the same app, resetting the balance to 10 rides, the researchers said.

"I can do that over and over again if I chose to," Benninger said during his talk. UltraReset works on Android 2.3.3 or later. (See a video of the researchers demonstrating the NFC hack in this Vimeo clip.)

The application takes advantage of a flaw found in particular NFC-based cards, the researchers said, adding that these cards are used in the San Francisco Muni and the New Jersey Path transit systems.

Both systems were tested by the researchers and both cities were informed about the possible abuse of the system, they said. "Both systems are still vulnerable as far as we know," said Benninger, who added that San Francisco was informed in December 2011.

The hack exploits the Mifare Ultralight chip used in disposable contactless NFC cards, the researchers said. This type of chip allows anyone who has the know-how to rewrite data to the NFC chip, they said. "I coded the app in one night," Benninger said, "and I'm not a coder so if somebody knows what they are doing it is pretty easy to do."

The Mifare Ultralight can work much like a standard punch card system, but instead of punching holes in a paper ticket the card can flip bits on to indicate that a travel unit has been used, the researchers said. Those bits can never be turned back, but in the vulnerable systems user information on the card is checked but the bits are never turned on, which enables exploiters to rewrite the cards, they added.

Other U.S. cities including Boston, Seattle, Salt Lake City, Chicago and Philadelphia also use a contactless ticketing system and those systems could also be vulnerable for the same technique, they said. Those systems, however, were not tested by the researchers, who said they had not been able to travel everywhere.

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