Technical Advisory – BLE Proximity Authentication Vulnerable to Relay Attacks


Many products implement Bluetooth Low Energy (BLE) based proximity authentication, where the product unlocks or remains unlocked when a trusted BLE device is determined to be nearby. Common examples of such products include automotive Phone-as-a-Key systems, residential smart locks, BLE-based commercial building access control systems, and smartphones and laptops with trusted BLE device functionality. The possibility of relay attacks against BLE proximity authentication has been known for years, but existing public relay attack tooling (based on forwarding GATT requests and responses) introduces detectable levels of latency and is incapable of relaying connections employing link layer encryption. Thus, products commonly attempt to prevent relay attacks by imposing strict GATT response time limits and/or using link layer encryption. Some systems also try to block signal amplification relay attacks through various localization techniques involving triangulation.

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