3 mins read
The carwhisperer project intends to sensibilise manufacturers of carkits and other Bluetooth appliances without display and keyboard for the possible security threat evolving from the use of standard passkeys.
A Bluetooth passkey is used within the pairing process that takes place, when two Bluetooth enabled devices connect for the first time. Besides other public data, the passkey is a secret parameter used in the process that generates and exchanges the so-called link key. In Bluetooth communication scenarios the link key is used for authentication and encryption of the information that is exchanged between the counterparts of the communication.
The cw_scanner script is repeatedly performing a device inquiry for visible Bluetooth devices of which the class matches the one of Bluetooth Headsets and Hands-Free Units. Once a visible Bluetooth device with the appropriate
device class is found, the cw_scanner script executes the carwhisperer binary that connects to the found device (on RFCOMM channel 1) and opens a control connection and connects the SCO links.
The carwhiperer binary connects to the device found by the cw_scanner. The passkey that is required for the initial connection to the device is provided by the cw_pin.pl script that replaces the official Bluez PIN helper (graphical application that usually prompts for the passkey). The cw_pin.pl script provides the passkey depending on the Bluetooth address that requests it. Depending on the first three bytes of the address, which references the manufacturer, different passkeys are returned by the cw_pin.sh script. In quite a few cases the preset standard passkey on headsets and handsfree units is ‘0000’ or ‘1234’.
Once the connection has been successfully established, the carwhisperer binary starts sending audio to, and recording audio from the headset. This allows attackers to inject audio data into the car. This could be fake
traffic announcements or nice words. Attackers are also able to eavesdrop conversations among people sitting in the car.
In order to avoid getting attacked by carwhisperer, manufacturers should not use standard passkeys in their Bluetooth appliances. Moreover, there should be some kind of direct interaction with the device that allows a device to connect. Another recommendation would be to switch the handsfree unit to invisible mode, when no authorized device connects to it within a certain time.
Not all Bluetooth carkits are subject to this threat. There is quite a few Bluetooth carkits that use random passkeys that are generated for every individual device during the production process. Carkits that are integrated with a full infotainment system could use (and sometimes already do use) the infotainment system’s UI for acquiring a passkey from the user.
Please use this Proof-of-Concept application responsible !
carwhisperer - Talk to Technophile Strangers (be nice)
(written for for Linux using BlueZ)
by Martin Herfurt
more information on the Car Whisperer project page
For questions about the Car Whisperer application, feel free to ask Martin Herfurt.
Martin is an independent security researcher focusing - but not exclusively - on various aspects of product security related to Bluetooth wireless technology. As one of the co-founders of the trifinite.group, Martin worked with the Bluetooth SIG, helping the technology and its adopters overcome early design and implementation issues.