Technical Advisory – Tesla BLE Phone-as-a-Key Passive Entry Vulnerable to Relay Attacks

Vendor: Tesla, Inc.
Vendor URL: https://www.tesla.com
Versions affected: Attack tested with vehicle software v11.0 (2022.8.2 383989fadeea) and iOS app 4.6.1-891 (3784ebe63).
Systems Affected: Attack tested on Model 3. Model Y is likely also affected.
Author: Sultan Qasim Khan 
Risk: <6.8 CVSS v3.1 AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N> An attacker within Bluetooth signal range of a mobile device configured for Phone-as-a-Key use can conduct a relay attack to unlock and operate a vehicle despite the authorized mobile device being out of range of the vehicle.

Summary

The Tesla Model 3 and Model Y employ a Bluetooth Low Energy (BLE) based passive entry system. This system allows users with an authorized mobile device or key fob within a short range of the vehicle to unlock and operate the vehicle, with no user interaction required on the mobile device or key fob. This system infers proximity of the mobile device or key fob based on signal strength (RSSI) and latency measurements of cryptographic challenge-response operations conducted over BLE.

NCC Group has developed a tool for conducting a new type of BLE relay attack operating at the link layer, for which added latency is within the range of normal GATT response timing variation, and which is capable of relaying encrypted link layer communications. This approach can circumvent the existing relay attack mitigations of latency bounding or link layer encryption, and bypass localization defences commonly used against relay attacks that use signal amplification. As the latency added by this relay attack is within the bounds accepted by the Model 3 (and likely Model Y) passive entry system, it can be used to unlock and drive these vehicles while the authorized mobile device or key fob is out of range.

Impact

If an attacker can place a relaying device within BLE signal range of a mobile phone or key fob authorized to access a Tesla Model 3 or Model Y, they can conduct a relay attack to unlock and operate the vehicle.

Neither normal GATT response latency nor successful communications over an encrypted link layer can be used as indications that a relay attack is not in progress. Consequently, conventional mitigations against prior BLE relay attacks are rendered ineffective against link layer relay attacks.

Details

NCC Group has developed a tool for conducting a new type of Bluetooth Low Energy (BLE) relay attack that can forward link-layer responses within a single connection event, and introduces as little as 8 ms of round-trip latency beyond normal operation. As typical connection intervals for this system are 30 ms or longer, and the added latency is within the range of normal response timing variation for BLE devices, the added latency can be made effectively invisible to the vehicle and phone software. Furthermore, this new type of relay attack can relay connections employing BLE link layer encryption, including following encrypted connections through parameter changes (such as changes to the channel map, connection interval, and transmit window offset).

This relay attack tool can be used for any devices communicating over BLE, and is not specific to Tesla vehicles.

Testing on a 2020 Tesla Model 3 running software v11.0 (2022.8.2) with 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. In the test setup, the iPhone was placed on the top floor at the far end of a home, approximately 25 metres away from the vehicle, which was in the garage at ground level. The phone-side relaying device was positioned in a separate room from the iPhone, approximately 7 metres away from the phone. The vehicle-side relaying device was able to unlock the vehicle when within placed within a radius of approximately 3 metres from the vehicle.

NCC Group has not tested this relay attack against a Model Y or in conjunction with the optional Tesla Model 3/Y BLE key fob. However, based on the similarity of the technologies used, NCC Group expects the same type of relay attack would be possible against these targets, given the use of similar technologies.

During experimentation to identify latency bounds, NCC Group discovered that relay attacks against the Model 3 remained effective with up to 80 ms of round trip latency artificially added beyond the base level of latency introduced by the relaying tool over a local Wi-Fi network. This latency margin should be sufficient for conducting long-distance relay attacks over the internet. However, NCC Group has not attempted any long distance relay attacks against Tesla vehicles.

Recommendation

Users should be educated about the risks of BLE relay attacks, and encouraged to use the PIN to Drive feature. Consider also providing users with an option to disable passive entry. To reduce opportunities for relay attacks, consider disabling passive entry functionality in the mobile app when the mobile device has been stationary for more than a minute. Also consider also having the mobile application report the mobile device’s last known location during the authentication process with the vehicle, so that the vehicle can detect and reject long distance relay attacks.

For reliable prevention of relay attacks in future vehicles, secure ranging using a time-of-flight based measurement system (such as Ultra Wide Band) must be used.

Vendor Communication

April 21, 2022: Disclosure to Tesla Product Security
April 28, 2022: Response from Tesla Product Security stating that relay attacks are a known limitation of the passive entry system.
May 9, 2022: Tesla Product Security notified of NCC Group’s intent to publish research regarding BLE relay attacks and their applicability to Tesla products.
May 15, 2022: Advisory released to public

Thanks to

Jeremy Boone for support and guidance throughout the research process developing this attack.

Editor’s Note (May 15 2022)

This research involves a generic link-layer relay attack on Bluetooth Low Energy, which affects products other than those mentioned here. That advisory was also published today and is available at:
https://research.nccgroup.com/2022/05/15/technical-advisory-ble-proximity-authentication-vulnerable-to-relay-attacks/

About NCC Group

NCC Group is a global expert in cybersecurity and risk mitigation, working with businesses to protect their brand, value and reputation against the ever-evolving threat landscape. With our knowledge, experience and global footprint, we are best placed to help businesses identify, assess, mitigate respond to the risks they face. We are passionate about making the Internet safer and revolutionizing the way in which organizations think about cybersecurity.

Published date: May 15, 2022
Written by: Sultan Qasim Khan