Security researchers at the NCC Group have developed a tool to carry out a Bluetooth Low Energy (BLE) relay attack that bypasses all existing protections to authenticate on target devices.
BLE technology is used in a wide spectrum of products, from electronics like laptops, mobile phones, smart locks, and building access control systems to cars like Tesla Model 3 and Model Y.
Pushing out fixes for this security problem is complicated, and even if the response is immediate and coordinated, it would still take a long time for the updates to trickle to impacted products.
How the attack works
In this type of relay attacks, an adversary intercepts and can manipulate the communication between two parties, such as the key fob that unlocks and operates the car and the vehicle itself.
This places the attacker in the middle of the two ends of the communication, allowing them to relay the signal as if they were standing right next to the car.
Products that rely on BLE for proximity-based authentication protect against known relay attack methods by introducing checks based on precise amounts of latency and also link-layer encryption.
NCC Group has developed a tool that operates at the link layer and with a latency of 8ms that is within the accepted 30ms range of the GATT (Generic ATTribute Profile) response.
“Since this relay attack operates at the link layer, it can forward encrypted link layer PDUs. It is also capable of detecting encrypted changes to connection parameters (such as connection interval, WinOffset, PHY mode, and channel map) and continuing to relay connections through parameter changes. Thus, neither link layer encryption nor encrypted connection parameter changes are defences against this type of relay attack.” – NCC Group
According to Sultan Qasim Khan, a senior security consultant at NCC Group, it takes about ten seconds to run the attack and it can be repeated endlessly.
Both the Tesla Model 3 and Model Y use a BLE-based entry system, so NCC’s attack could be used to unlock and start the cars.
While technical details behind this new BLE relay attack have not been published, the researchers say that they tested the method on a Tesla Model 3 from 2020 using an iPhone 13 mini running version 4.6.1-891 of the Tesla app.
“NCC Group was able to use this newly developed relay attack tool to unlock and operate the vehicle while the iPhone was outside the BLE range of the vehicle” – NCC Group
During the experiment, they were able to deliver to the car the communication from the iPhone via two relay devices, one placed seven meters away from the phone, the other sitting three meters from the car. The distance between the phone and the car was 25 meters.
The experiment was also replicated successfully on a Tesla Model Y from 2021, since it uses similar technologies. Below is a demonstration of the attack:
These findings were reported to Tesla on April 21st. A week later, the company responded by saying “that relay attacks are a known limitation of the passive entry system.”
The researchers also notified Spectrum Brands, the parent company behind Kwikset (makers of the Kevo line of smart locks).
What can be done
NCC Group’s research on this new proximity attack is available in three separate advisories, for BLE in general, one for Tesla cars, and another for Kwikset/Weiser smart locks, each illustrating the issue on the tested devices and how it affects a larger set of products from other vendors.
The Bluetooth Core Specification warns device makers about relay attacks and notes that proximity-based authentication shouldn’t be used for valuable assets.
This leaves users with few possibilities, one being to disable it, if possible, and switch to an alternative authentication method that requires user interaction.
Another solution would be for makers to adopt a distance bounding solution such as UWB (ultra-wideband) radio technology instead of Bluetooth.
Tesla owners are encouraged to use the ‘PIN to Drive’ feature, so even if their car is unlocked, at least the attacker won’t be able to drive away with it.
Additionally, disabling the passive entry functionality in the mobile app when the phone is stationary would make the relay attack impossible to carry out.
If none of the above is possible on your device, keep in mind the possibility of relay attacks and implement additional protection measures accordingly.
