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My new Microsoft Surface Book let’s me switch to 3rd party CAs or even none at all, with no problem. This sounds like a Lenovo issue. On top of that, I would p
by helloooooooo 4y ago
My new Microsoft Surface Book let’s me switch to 3rd party CAs or even none at all, with no problem. This sounds like a Lenovo issue.
On top of that, I would prefer if my machine is by default, in a secure configuration when I buy it. Since the laptops come with Windows pre-installed and Microsoft signed bootloaders, it is fundamentally more secure than if the 3rd parties CAs are enables. I don’t want an attacker chain loading Linux and KVM beneath my Windows OS.
- cptskippy 4y ago> This sounds like a Lenovo issue. Lenovo locks down hardware. I tried to upgrade the WiFi card in my Yoga 2 and got an "unauthorized hardware" message from the UEFI and it refused to boot until I removed the hardware. I would not at all be surprised if they're just over reaching.
- Arnavion 4y ago>I don’t want an attacker chain loading Linux and KVM beneath my Windows OS. If your Windows install was protected by Bitlocker, and the decryption key was stored in the TPM, and the TPM was set up to require attestation to unseal the key, then such chainloading wouldn't be an issue. (This is also explained in the article.) BTW, the default for the firmware interface is that it is not password-protected, so even this particular Lenovo device is vulnerable to the evil maid attack you're describing in its "default secure configuration", because the maid can just toggle that option to enable the UEFI CA, or even disable SB entirely. Unless Lenovo is planning to make the UEFI password a required step in their purchase order process, you can expect that the default configuration is going to be an unprotected UEFI. That's why the way to resolve the threat is not to prevent other bootloaders, but to prevent them from reading the data on disk.
- tjoff 4y agoIt is still an issue. A different OS could load and mimic the normal boot procedure to steel any credentials entered. Also, the whole scenario you depict is quite unreasonable to expect of a default install - which is exactly what is being talked about.
- Arnavion 4y ago> It is still an issue. A different OS could load and mimic the normal boot procedure to steel any credentials entered. What credentials? The bitlocker key is in the TPM. It's not something a human can enter. >Also, the whole scenario you depict is quite unreasonable to expect of a default install - which is exactly what is being talked about. I'm confused. Are you referring to the scenario of the Windows install with the bitlocker key in the TPM, or the scenario of the evil maid attack? The former is already how Windows works by default, and the latter is precisely the scenario that helloooooooo was talking about, so I'm not sure which one you're calling unreasonable.
- tjoff 4y agoAnd normal people unlock bitlocker is by entering a passphrase. If you have the passphrase you can unlock it...
- AshamedCaptain 4y agoNot really; most people unlock Bitlocker via TPM, that's why a shitton of people don't even realize they have it. If the TPM doesn't give up the key, you are asked for the _recovery key_, not a passphrase. And the fact they have no clue what the "recovery key" is, that is how most people realize they had Bitlocker on... MS actually keeps a copy of _your_ PC's recovery key on their servers when you install Windows; that's one of the official reasons they have for requiring a MS account when you set Windows up: so that they can store your recovery key for you and give it back to you if ask nicely. (Moral implications of this best left for another discussion). This is for the personal editions of Windows, in the business editions of Windows; your IT (via ActiveDirectory) will store your recovery key for you.
- tjoff 4y agoI know. So walk me through it, you turn on the machine. Windows boots, you are greeted with a login/password prompt. The user enters their password and now typically have access to everything of value on that machine.
- helloooooooo 4y agoYes an attacker still could. BitLocker is handled within Microsoft binaries in the windows EFI partition. I believe it is specifically bootmgr.efi. You can still chain load up windows on KVM at this point, however getting the Windows partition decrypted may be difficult and requires faking up a few TPM measurements.
- AshamedCaptain 4y agoYou cannot "fake a few TPM measurements", it is the TPM itself which decides whether to give up the key or not.
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