IoT security is a hot topic these days, and rightly so. Matthew Garrett has spent a lot of time reverse engineering various IoT light bulbs to determine how secure they are, with depressing results. So when I saw Bruce Schneier’s recent post Security Analysis of the LIFX Smart Light Bulb which started with “it’s terrible” I thought this was more of the same. Except it’s not. The original article is Pwn the LIFX Mini white (and the author has at least a couple of other device teardowns in the same vein).
What these articles are concerned with is not the usual protocol level security which Matthew investigates. Instead they’re about physical device security. In particular the points raised are:
- Wi-Fi details are stored in the clear on the device
- The device does not have secure boot or flash encryption enabled
- The private key for the device can be retrieved easily
All of these boil down to the same root cause; without effective DRM there is no way to protect devices from physical attacks. That can be as simple as having only internal flash and being able to blow a set of EFUSEs to prevent readout/debug interfaces functioning, or it can be a full built in boot ROM with cryptographic verification of an image pulled in from external flash (potentially encrypted) and the building up of a chain of trust. I see 2 main problems with this.
Firstly, getting security like this right is hard. Games console manufacturers are constantly trying to protect their devices against unauthorised code running, and while they seem to be getting better it’s taken quite a number of mistakes to get there. They have a much bigger financial imperative to get this right, as console DRM attacks are frequently used for piracy. An IoT vendor could end up adding significant cost to their BoM if they have to buy a more advanced chip to be able to do the appropriate end-to-end flash encryption required. (The LIFX is using the ESP32, which does have some of these features that are not present in the more basic (and cheaper) ESP8266. I’ve no idea if anyone has done a full analysis of the ESP32 security.)
Secondly, locking devices down in this way has a big impact on user freedom. It should come as no surprise that this is my primary concern, as I believe it is detrimental to the end user in multiple ways.
- There’s a lot of poor security in the IoT protocol arena. If it’s not possible for anyone other than the manufacturer to update a device, or retrieve the firmware image to examine how a device operates, security will suffer.
- Updates being locked down to the manufacturer leaves the user open to the prospect of forced obsolescence when the manufacturer decides they will no longer support the device, or goes out of business (assuming a device that has some sort of cloud component).
- Part of the appeal of a lot of the current IoT devices is the fact they can be repurposed for uses beyond what the manufacturer imagined. Just look at the Sonoff-Tasmota project - this excellent 3rd party support is one of the main reasons I purchased several Sonoff devices. If I hadn’t been able to replace the firmware they wouldn’t have been of interest to me or countless other people who’ve purchased them.
There are ways to enable user freedom while still having a locked down setup by default, but they’re hard to do in the embedded IoT space (generally no hardware infrastructure that allows plugging in a USB stick with a new root certificate on it and enrolling it like EFI Secure Boot), and add significant cost and complexity to devices that are meant to be cheap and ubiquitous. I see the validity in raising concerns about discarded devices leaking Wi-Fi credentials, but it’s something any device you connect to your Wi-Fi is potentially going to do. That means your laptop, your phone and all the random other devices you allow to connect to your Wi-Fi. It’s something we need to be aware of generally, rather than singling some cheap IoT light bulbs out.
The lack of physical security for the firmware image or device credentials is not so worrying to me. A surveillance device in a light bulb is not a new concept; in fact the added complexity of an IoT bulb makes it easier to justify the complex circuitry being present. If it requires physical access to be able to subvert the device like this that’s significantly less worrying than being able to do so remotely.
Don’t get me wrong, I love a good device teardown, and I think there’s an interesting discussion that’s already underway about how to improve physical device security without restricting user freedom. I just don’t think this is the major failure that some commenters are suggesting.