CVE-2019-17627

Vulnerability

The Yale Bluetooth Key application for mobile devices communicates with door locks via Bluetooth Low Energy (BLE). The authentication protocol uses an 8-byte key (keyString) that can be derived by sniffing a single authorized unlock session. The lock sends an authentication request, and the app responds with a computed response. By reversing the app, the function encodeCounter reveals that the key is split into six parts and added to the request payload to produce the response. This allows an attacker to calculate the key offline. Affected devices include the Yale ZEN-R lock and unspecified other locks. [1]

Exploitation

An attacker must be within BLE range to sniff the communication between a legitimate phone and the lock during an authorized unlock. Using a low-cost BLE sniffer (e.g., a $5 USB dongle), they capture the authentication request and response packets. Then, by subtracting the request payload bytes from the response payload bytes (as per the encodeCounter algorithm), the attacker recovers the six parts of the authentication key. No authentication or user interaction beyond sniffing is required. [1]

Impact

Once the attacker obtains the 8-byte authentication key, they can unlock the door from any Bluetooth-enabled device by replaying the computed authentication response. This results in unauthorized physical access to the secured area. The confidentiality, integrity, and availability of the lock are compromised, allowing lock bypass without any cryptographic secrets. [1]

Mitigation

No fix or patch has been disclosed in the available references. Users of affected locks should monitor for firmware updates from Yale and consider disabling Bluetooth access if not needed. Until a fix is released, the vulnerability remains exploitable via physical proximity. [1]