Researchers have demonstrated that the Z-Wave wireless communications protocol, which is used by more than 100 million Internet-of-Things (IoT) devices, is vulnerable to security downgrade attacks.
Z-Wave, a protocol primarily used for home automation, uses low-energy radio waves for wireless communications over distances of up to 100 meters (330 feet). Z-Wave was developed by Zensys in 2001 and in 2008 it was acquired by Sigma Designs, which recently sold it to Silicon Labs for $240 million.
According to the Z-Wave Alliance, an organization dedicated to advancing Z-Wave, the protocol is currently used by 700 companies in over 2,400 IoT and smart home products, including thermostats, locks and home monitoring systems.
UK-based Pen Test Partners has conducted an analysis of Z-Wave and discovered that a hacker in range of the targeted devices during the pairing process can launch an attack and crack supposedly secure communications.
The researchers demonstrated their findings on a Yale smart lock – they showed how an attacker can unlock a door – but the method, which they have dubbed “Z-Shave,” works against any device using Z-Wave.
Z-Wave relies on a shared network key to secure traffic between the controller and the client device when they are paired. The initial version of the pairing process, known as S0, was found to be vulnerable to sniffing attacks back in 2013, which led to the introduction of a more secure process named S2.
The problem with S0 is that it protects the network key with a known encryption key (0000000000000000), allowing an attacker in range of the targeted device to intercept communications. S2 addresses this problem by using stronger encryption, but researchers discovered that an attacker can downgrade the connection from S2 to S0, basically removing the protection.
The hacker needs to be present during the initial pairing process to perform the downgrade, but Pen Test Partners pointed out that the attacker could use a battery-powered hacking device that is left outside the targeted property for an extended period of time, waiting for the pairing process to be initialized.
“The risk is mitigated as one has to be present during the pairing process, but the Z-Wave RF range is significant. We’re investigating whether it might be possible to de-authenticate a Z-Wave client device, but that’s work in progress,” researchers explained.
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.
In a blog post published on Wednesday, Silicon Labs assured users that the risk is low and highlighted that it’s not aware of any real-world exploitation.
“While it’s possible that an attacker could intercept the S0 encrypted key exchange frame and decipher it using the hardcoded key, this is only possible during the initial set-up or reinstallation of the device,” Silicon Labs said. “To do this, the attacker would need to be within close proximity of the device during the very moment the device is installed – an extremely small window of opportunity. Furthermore, Z-Wave devices can switch their radio to low power transmission mode during key exchange process to make packet interception attack much more difficult.”
The company added, “It would not be possible to execute an attack without the homeowner becoming aware because they would receive a warning from the S2 controller during the pairing process.”
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