IoT and Stuff – Cautionary Tales

Overview

IoT (Internet of Things) is an interesting phenomena where “things” become connected and provide either some control and / or sensor capability through this connection. Examples include connected thermostats, weather stations, garage door openers, smart door locks, etc.

It is an area of explosive growth, and like any other system it will have its security failures.

Tale 1 – Hacking Internet Connected Light Bulbs

LIFX lightbulbs are smart LED lights with two wireless interfaces; a Wi-Fi interface to connect to the local network and provide a control path for computers / smartphones, and an IEEE 802.15.4 mesh network to communicate between multiple LIFX smartlights. This dual wireless interface meant that any number of LIFX smartlights could be controlled and managed through a single Wi-Fi connection. Since any of the LIFX smartlights could operate as the “master” device that connected to both networks, it was necessary for each smartlight to have the Wi-Fi network access credentials.

Vulnerability

The vulnerability involves a couple of aspects in the design. These include:

  1. When an additional LIFX smartlight was added to the network, it exchanges data over the IEEE 802.15.4 network in the clear (unencrypted); except for the Wi-Fi credentials and some configuration details. All of this data was sent as encrypted blob.
  2. The encryption key for this blob was a pre-shared key hard coded into the firmware for every LIFX smartlight (of that firmware revision). This key was accessible via JTAG (which was pinned out on the PCB) or through the firmware image (which was not available at the time of the compromise).
  3. The system allowed a client on the IEEE 802.15.4 network to request (and receive) this encrypted configuration / credentials blob at any time in the background.

Compromise

The compromise allows an attacker physically close to the system to:

  1. Acquire the LIFX pre-shared encryption key from the firmware or JTAG interface.
  2. On the IEEE 802.15.4 network, request the encrypted configuration / credentials blob (masquerading as a LIFX smartlight).
  3. Crack open the blob using the encryption key from step 1.
  4. Connect to the Wi-Fi network using the credentials from the blob.
  5. Access the network and / or control the LIFX light bulbs.

Assessment

From this there are at least a few poor design choices that enabled this compromise. The first of these is to use a static pre-shared key to encrypt sensitive wireless data. The ability to establish a secure channel based on PKI has been standard practice for decades, allowing the use of dynamically generated keys at a session level. The use of a static pre-shared key is just lazy design.

The second of these is the ability to request the encrypted credential blob silently. For an initial configuration of an additional smartlight to the network, it is reasonable to require user confirmation to share the data with the additional smartlight. An attacker requesting this data in the background should not be allowed to get this data without user confirmation, or simply rejected when not part of a new bulb configuration.

Although having the JTAG port pinned out may seem to be a poor design choice, it is not really add significant risk. JTAG availability on the device pins would have been more than sufficient for a physical hacker, and that is assuming that the same data would not have been available in a firmware download. A JTAG port does not present a significant risk if keys are managed securely, and the security architecture takes this exposure into account.

Tale 2 – Smart Home Denial of Service

Vulnerability

The vulnerability in this story is that the smart home in this story had connected all of the smart devices in the house through a common Ethernet infrastructure – effectively rendering every device as a node on a flat network. This flat network meant that any one device can saturate the network with packets, effectively breaking the network. It also means that any one device can also monitor every packet on the network, or selectively disrupt packets. Essentially the security of this flat network can be compromised in multiple ways by any device on the network, and the overall security of the network is only as good as the weakest device.

Compromise

This particular compromise was based on a smartlight beaconing on the network as a denial of service attack. This event was not malicious, but if we consider the triad of confidentially, integrity and availability it is still a security failure. A self induced denial of service is still a denial of service.

Assessment

As a systems engineer the smart home described in this article makes me uncomfortable. The designer indicated that he had not installed his smart door locks since he did not want to be locked out / in by the locks. The designer also indicated that the light bulb denial of service rendered all the smart devices in his house broken / unavailable.

As a systems engineer this bothers me for a couple of reasons. The first of these is that it is possible to segment the network so that a failure does propagate through the entire network – effectively setting up security domains on functional boundaries. Even a trivial level of peering management would provide some level of isolation without giving up the necessary control protocols.

The second part that I find bothersome is that it appears that the entire system was designed with a single centralized control mechanism / scheme. Given the relatively poor reliability of network systems as compared with traditional home lighting / appliance controls, it makes sense to to install a parallel control scheme that is based on a local (more reliable) control path that operates much closer to the device being controlled.

In summary – the architecture of this particular smart home implementation is brittle in that a single device failure can precipitate an entire system failure. In addition it is fragile in that the control scheme is dependent on a number of disparate sequential operations that provide a multitude of single point failures for every device. Lastly, the system is not robust in that there is not an alternate control scheme. In my opinion this smart home may be an interesting experiment, but is a weak systems design with lots of architectural / system flaws.

Tale 3 – ThingBots

This is not a cautionary tale about a specific device or attack, but a cautionary tale about embedded devices in general, and by inclusion – IoT devices. Back in last week of 2013/first week of 2014, Proofpoint gathered some data from a number of botnets sending out spam. Specifically, they identified the unique IP addresses in the botnets, and characterized them forensically, and found that roughly a quarter of the zombie machines were not traditional PCs, but things like DVRs, security cameras, home routers, and at least one refrigerator. From this they coined the term ‘ThingBot’, which is a botnet zombie based on some ‘thing’.

The message is that when it comes to compromise and attack, there are no devices that will not be attacked, there is no point where your devices is not a target for a botnet. Harden all embedded devices and design defensively.

Bottom Line

The messages in these three tales are diverse, but can be summarized by:

  1. Every connected device is a target. Simply being a connected device is sufficient.
  2. Key management may be mundane but is even more critical on devices since often the only interface is networked.
  3. Most importantly РSystem design matters. Most security issues occur at the integration  interfaces between components of one type or another Рand good system design reduce that exposure.

References

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