Firmalware

There’s a fascinating story from Reuters (with a far more detailed report from Kaspersky) about how a very sophisticated hacking operation, presumably the NSA, has been targeting computers by reflashing the firmware of hard drives such that the attacker controls what is loaded at boot time. If you think this has shades of Stuxnet about it, then you aren’t alone.

Why am I posting this? Well I think in the embedded community there’s been a certain amount of nonchalance concerning malware attacks on firmware, aka Firmalware. I see a lot of shrugs – it’s firmware, so it’s not modifiable, or who wants to take control of X, or to attack it they will need the source code and so on. Well if you read the articles – and I strongly recommend you do, then you’ll read that the attacker almost certainly did get hold of the source code for the disk drives, that they exploited undocumented commands, that they reprogrammed the disk drive firmware and that they proceeded to take complete control of the victim’s computer.

So what’s this to do with you? Well I strongly urge you to consider the consequences of what would happen if an attacker took control of the gadget you are working on. For example, sitting on my desk right now is a USB dongle used to receive over the air digital TV broadcasts. It doesn’t sound like it’s a great avenue for exploitation. However, an attacker could easily do the following if they had control of this device.

  1. On broadcast (i.e. over the air) command, switch the dongle into acting like a USB drive. USB drives are a major source of malware infection.
  2. Again on broadcast command, force the dongle to tune to a specific frequency resulting in the user being exposed to whatever the attacker wishes them to.

Although I’m not exactly the paranoid type, it really doesn’t take much imagination to work out how legions of embedded devices could be made to do some rather nasty things to their users.

The bottom line. If you haven’t thought about what happens if an attacker gets control of your gadget then you aren’t doing your job. Some things to ponder:

  1. How secure is your source code?
  2. If you have a bootstrap loader, how secure is it?
  3. When you distribute new firmware for installation on your gadget, is it distributed in encrypted form?
  4. Even if it’s distributed in encrypted form, is it downloaded in encrypted form?
  5. How do you protect the encryption keys?
  6. Are you setting the lock bits correctly so as to at least make binary extraction more challenging. (However don’t get too cocky)

The list could go on – but I think you get the idea.

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