A Dutch electronics engineer reckons Japanese auto-maker Subaru isn't acting on a key-fob cloning vulnerability he discovered.

Tom Wimmenhove claims to have discovered that Subaru's electronic keys don't use a random number. The “rolling code” instead merely increments codes.

Wimmenhove says he's built a cloning device (described here on GitHub) and used it on a 2009 Subaru Forester, but believes it would also work on a 2006 Baja, Forester models from 2005 to 2010, Impreza models from 2004 to 2011, the "Legacy" sedan's 2005 to 2010 models and the Outback from 2005 to 2010.

His test rig is only worth about US$25, comprising a Raspberry Pi, a DBV-T USB dongle to provide the radio receiver, and rpitx software (here) that turns the RPi into a transmitter. A suitable antenna is required so the receiver can detect signals at 433 MHz.

Because the key fobs simply increment the rolling code exchanged between car and key, all an attacker needs is to be close enough to capture the code used when the owner locks the car; incrementing that code lets the attacker unlock the car.

Here's Wimmenhove's demonstration:

Youtube Video

The attack has another nasty aspect: the attacker can brick the owner's key fob with an integer overrun: “increasing the rolling code with a sufficiently high value [will] effectively render the user's key fob unusable”, Wimmenhove writes.

A spokesperson for Subaru was not available for comment. ®