The Z-Wave specification requires that S2 security can be downgraded to S0 or other less secure protocols, allowing an attacker within radio range during pairing to downgrade and then exploit a different vulnerability (CVE-2013-20003) to intercept and spoof traffic.

Z-Wave devices from Sierra Designs (circa 2013) and Silicon Labs (using S0 security) may use a known, shared network key of all zeros, allowing an attacker within radio range to spoof Z-Wave traffic.