Despite security measures in place, researchers have found how to analyze and exploit Bluetooth transmissions for tracking mobile devices. Although the methodology has some limitations, it still poses a significant threat to users.
Mobile Devices Tracking Via Bluetooth Transmissions
Researchers from UC San Diego have shared a detailed research paper about tracking mobile devices by analyzing Bluetooth transmissions.
In brief, the technique works on the analysis of the beacons that devices mobile devices transmit when using the Bluetooth Low Energy (BLE) protocol.
Although, it always remains technically possible to track these beacons since the devices continuously transmit them for communication with available recipient devices when needed. However, the devices implement various measures to prevent such unsolicited Bluetooth tracking, like re-encrypting MAC addresses.
Nonetheless, the researchers have now elaborated on bypassing the security measures to stalk the beacons.
The process basically involves fingerprinting the unique physical layer to identify target devices. This fingerprinting remains unaffected even if the MAC address resets.
Regarding how the attack executes, the researchers explain,
First the attacker must isolate the target to capture a fingerprint of its wireless transmissions. Then it must find features that uniquely identify the target, namely the unique physical-layer features of the device’s BLE transmitter hardware. Then, the attacker sets up a receiver in the location where they want to see if the transmitter is there and passively sniffs for the target’s BLE transmissions. They will know when the target device is near the receiver when it captures one or more packets that matches the target’s physical layer fingerprint.
Once fingerprinted successfully, the adversary can then stalk the victim whenever accessible, particularly when the target device transmits more frequently.
All it takes for an adversary to execute this attack is bearing a Software Defined Radio sniffer that can record g raw I/Q radio signals.
Attack Limitations And Countermeasures
Despite being easy, the method also has some limitations that make it a presently impractical threat in a real-world scenario.
For instance, temperature changes can impact device metrics to cause changes in the fingerprint. Likewise, two or more devices may exhibit similar fingerprints, thereby alleviating the uniqueness for device identification. Similarly, tracking the target device becomes difficult if the device has a low transmit power.
As for countermeasures, the researchers explain that applying fixes at the software level isn’t enough since the method makes use of hardware.
Nonetheless, a simple workaround can come into action if the device workload keeps on changing with the MAC address. Such workload fluctuations will also trigger changes in battery consumption and the device temperature. However, constantly high temperatures may damage the battery life.
Another proposed countermeasure is redesigning the BLE chipset signal chain by “adding random time-varying extra frequency offset the crystal oscillator.”
The researchers have shared the code for this project on GitHub for all to review.
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