I don't see any encryption bypass there.
Encrypted partition stays encrypted.
> From here it’s easy to manually use the TPM to unlock the disk with the Clevis tooling and mount the root volume for hacking (it takes a few tries sometimes, but it gets there in the end):
They use the exploit to get dropped into a root shell, and then asks the TPM to unlock the disk for them, which it promptly does.
That's not to say that an improvement can't be made as we move towards a future where TPM+LUKS might be the norm - just that you can't retrospectively claim fault on an OS that doesn't claim to support that.
And it still is perfectly reasonable behavior. Any distribution that decides (perhaps as a consequence of this) that on any boot process abnormality the default response is to enter an immediate reboot loop would be called crazy.
It’s still looks perfectly reasonable, just PCR should be fed with some value before that, maybe a hash of initramfs file? It seems to be reasonable as at this moment the state of the operating system differs from the one properly booted, which seems to fit the idea of secure boot.
This way it would be possible to still unlock LUKS with a pass phrase but not access TPM keys locked for configuration when initramfs shell is not running.
I agree with the logic that by default the OS is doing the right thing without any changes to support this model.
Like, you are dropping a general purpose computer into the middle of Russia, expect to be able to command it remotely to do anything, even remotely update it and reboot it; and at the same time never bother to come check it up in person or even have minimum chassis intrussion detection. Do people really expect this to work just by adding some TPM craziness?
The article is just connecting a keyboard sniffer/simulator but it would have been as easy to do anything to the network traffic, SSD, motherboard/CPU JTAGs, RTC, etc.
Games consoles are super locked down, to prevent piracy, and some modern consoles have gone years without a successful hack, despite being in the physical possession of the attacker. The iphone's activation lock is extremely hard to bypass, and even cops and border guards struggle to extract users' data.
Simply buy your PC from your operating system vendor directly, and forego options like being able to replace components and being able to install your own software, allowing the memory and PCI bus to be encrypted. Add some cloud backup features so the device can wipe itself at the drop of a hat without losing your data. After that, just have your OS vendor produce perfect code with no exploits, and you're secure!
Simple! /s
But it isn't so not the OSes problem.
However screenshot says 'Unsealing failing'. Yet Ubuntu-lv is mounted. I don't follow how Luks password was guessed for it.
Secure Boot with TPM-backed disk encryption works off of a series of numbered hashes. The idea of TPM based FDE is that the machine will use Secure Boot to boot only a software chain that the end-user trusts not to contain authentication bypasses. In Secure Boot, the EFI firmware provides hashes of each stage in the boot chain to the TPM, and the TPM only unlocks the full-disk encryption key (really the key encryption key, since the TPM isn't fast enough to actually decrypt the disk) slot if each stage / configuration is valid.
This issue breaks that chain. In some sense it's an illustration of this system being silly conceptually, but it is a real issue IMO.
I'm not sure why you would rely on just the TPM in this case, though. TPM only disk encryption is rather risky, you'd expect a TPM+PIN setup at the very least.
You'd still be at risk because of this flaw, because the root shell would allow sniffing the key from a secure session. Ideally, attempts to brute force the user account should prevent further attempts by rebooting or refusing further interactive input.
I think the target market is "I have a server in a data centre, I need unattended boot, I don't really need a high grade of security I just need to tick a checkbox saying the hard disk is encrypted"
If your organisation is large enough to start losing track of entire servers, and yet small enough you can't adopt effective organisational controls to prevent such losses, even mediocre encryption might give you some peace of mind - and it lets you avoid reporting data breaches, as the lost data was 'encrypted'.
So there we are somewhat breaking 'Secure Boot' process in general.
Also allows you to do that when you retire a server or cluster. I've been in situations where we had to wipe hundreds of multi-TB hard drives. If you've never done it, that takes a good deal of time. You can get appliances that do it, or try to build your own DBAN rig, but it still takes days. Or you can just shred them, but hard drive shredders are not cheap either, and that's rather wasteful and may not be environmentally conscious.
A large organisation will usually have tedious checks and record-keeping for wiping and discarding hardware, probably instituted after they wiped and discarded the wrong hardware.