Snippet 15: Bluetooth Impersonation Attacks

BIAS, Bluetooth Impersonation AttackS, exploits a flaw in the Bluetooth standard itself: unilateral authentication in Legacy Secure Connections lets a third party impersonate either paired device, and attackers can downgrade even securely paired devices back into the vulnerable mode just by asking.

Key Takeaways

• BIAS is a standards-compliant attack, exploiting a hole in Bluetooth itself rather than a vendor bug
• It lets an attacker impersonate either side of a paired connection, affecting devices up to Bluetooth 5 across 28 chipsets
• Legacy Secure Connections allow unilateral authentication, and arbitrary role reversal lets either party be impersonated
• Devices paired with the stronger Secure Connections mode can be downgraded back to the weak legacy mode on request

Video Transcript

First one I want to talk about is the Bluetooth impersonation attacks. It's a suite of attacks. And the acronym here is BIAS. So these are the researchers. And you can go check it out. If you just Google BIAS Bluetooth, you'll get to their page where they've got all kinds of great information. There's a couple of categories and types of attacks. This one happens to be a standards compliant attack. What that really means is that there's a hole in the Bluetooth standard they exploited.

Other attacks depend on an incorrect implementation of Bluetooth. This doesn't rely on that. It just the Bluetooth standard had a bug in it basically. And the result of the attack is that an attacker, if you've got a pair of Bluetooth devices, Alice and Bob, an attacker, a third person can impersonate either one of those ends and then take over the communication. Affects all the way up to Bluetooth 5. And they've demonstrated on 31 devices and 28 unique chipsets from all the big names that we've heard of.

So a little background before the next slide where I dig into how it works exactly, when Bluetooth devices authenticate, they share a long-term key when they first pair. And then in subsequent sessions, they generate session keys using that long-term key and other parameters that are transmitted unencrypted and clear, like their Bluetooth address. So there's this session key is the takeaway point there. The other point to keep in mind is that Bluetooth allows either party to switch roles. So in this case, Bob is the master.

But unilaterally, prior to authentication, Bob and Alice can switch roles. So Alice would become the master and in effect, become the authenticator. So the diagram here shows the net result is that Charlie, the attacker, can either impersonate Bob or Alice. So how does it work? It works by exploiting Legacy Secure Connection mechanism in Bluetooth. It's called Legacy Secure Connection, LLC. And that allows for unilateral authentication. So the master can send its challenge, the slave sends its response. And the master actually doesn't verify.

He can unilaterally choose to not verify and thus establish the connection. So it works in LLC mode when you want to impersonate the master, but it also works if you want to impersonate Alice, the other party in the attack. And that's because Bluetooth allows for arbitrary role reversal. And then the last bullet, which is interesting, is that Bluetooth has a more secure authentication scheme that requires mutual authentication instead of unilateral authentication called Secure Connection, SC.

But researchers show that either party can unilaterally downgrade both connections to the LLC authentication by just asking. And that was even true if the original devices paired and did their original key exchange using SC mode. So here's a plot from their paper that shows how the affected devices in LLC mode. And then not all devices suffered from that downgrade attack where you could unilaterally move back to LLC. And this shows master impersonation and slave impersonation.

So in LLC mode, if that was the initial pairing, all these devices were vulnerable.