Researchers from Pen Test Partners have conducted an analysis of Z-Wave wireless communications protocol used by millions of IoT devices and discovered that it is vulnerable to cyber attacks.

The Z-Wave protocol is widely adopted for home automation, it leverages low-energy radio waves for wireless communications over distances of up to 100 meters (330 feet).

The protocol is currently used by 700 companies in over 2,400 IoT and smart home products.

Z-Wave uses a shared network key to secure communications among devices, the key is exchanged between the controller and the client devices when the devices are paired.

The earlier pairing process (‘S0’) had a vulnerability – the network key was transmitted between the nodes using a key of all zeroes, and could be sniffed by an attacker within RF range.

The initial version of the pairing process (S0) is known to be vulnerable to MITM attacks since 2013, for this reason, experts introduced a more secure process named S2.

While S0 was using a known encryption key (0000000000000000), S2 leverages stronger encryption, but the experts found a way to force a downgrade of the pairing process from S2 to S0.

The white hat hackers discovered that an attacker in range of the targeted devices during the pairing process (‘S0’) can easily sniff the network key because it was shared between

The experts dubbed the attack “Z-Shave,”

“The earlier pairing process (‘S0’) had a vulnerability – the network key was transmitted between the nodes using a key of all zeroes, and could be sniffed by an attacker within RF range. This issue was documented by Sensepost in 2013. We have shown that the improved, more secure pairing process (‘S2’) can be downgraded back to S0, negating all improvements.” reads the analysis published by the experts.

“Once you’ve got the network key, you have access to control the Z-Wave devices on the network. 2,400 vendors and over 100 million Z-wave chips are out there in smart devices, from door locks to lighting to heating to home alarms.”

The experts published a video PoC of the attack on a Yale smart lock “Z-Shave,” works against any device using Z-Wave.

Researchers at Pen Test Partners explained that an attacker could use a battery-powered hacking device that is left outside the targeted building waiting for the pairing process to be initialized.

“A downgrade to no security may sound like it has more serious impact, but it means that the attacker cannot obtain the S0 network key. This means the only node placed at risk is the one just added. If an S0 network key is obtained, all S0 devices connected in the past and future are placed at risk.” explained the experts.

“The bigger difference is that our attack can be carried out by an active attacker within RF range at the time of pairing. And when we say active attacker – we don’t mean a guy in a hoody sat in a car with a laptop. A battery-powered drop-box could be left outside the property for weeks, waiting for a pairing event to occur.”

It turns out that a variant of this downgrade attack was discovered last year by cybersecurity consulting firm SensePost, but the vendor told experts at the time that this was by design and needed for backwards compatibility.

The experts explained that the Z-Wave Alliance still hasn’t addressed the issue, a delay that could have serious consequences.

“We aren’t certain how backward compatibility with S0 can be supported whilst enforcing stronger S2 security. This underlines the challenge with many protocols: how do you improve security without creating mountains of electronic waste for devices that are no longer supported?” concluded the experts.

“At the very least, the user should be fully alerted to the fallback to weak security.”

Pierluigi Paganini

(Security Affairs – Z-Wave, hacking)

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