Technology

@marcan@treehouse.systems (Hector Martin from Asahi Linux) said the following on Mastodon:

Ars headline: "Found in the wild: The world’s first unkillable UEFI bootkit for Linux"

Article then proceeds to describe a toy GRUB wrapper bootkit that has nothing to do with UEFI firmware (other than running on UEFI systems like any other UEFI bootloader), does not persist in UEFI firmware whatsoever (it just is installed in the ESP partition on disk), and can be killed by not just a drive swap, but any OS reinstall, and even simply a GRUB update/reinstall.

And which looks like a toy demo from every angle, that any experienced security researcher could have cooked up in a couple afternoons. Hardcoded kernel patch offsets for a single specific Ubuntu kernel build and all. No novel techniques in use. This could have even been a homework exercise as far as I'm concerned.

In fact, it has an obvious mistake, touched on by the original article: LD_PRELOAD is set to a string trailing with " /init", no doubt a copy+paste of the command line used to achieve the same execution during testing. The correct string would have omitted the " /init", and the mistake would have caused an error message like this to be printed for every executable launched until LD_PRELOAD is overridden:

ERROR: ld.so: object '/init' from LD_PRELOAD cannot be preloaded (invalid ELF header): ignored.

Furthermore, this bootkit is incomplete, since it relies on chaining into components installed via another mechanism (e.g. /opt/injector.so in the initramfs). A true bootkit only relies on its own first stage to drop all subsequent stages. That's the whole point of setting up a boot chain compromise like this. Otherwise you can defeat it by removing any of the stages, even if the bootkit stage is intact. As it stands, this bootkit isn't really a bootkit, it's just a module signing side-step that allows a traditional rootkit to be loaded on a system with Secure Boot enabled (and, since the Secure Boot is still working as intended, that results in a prompt on the first reboot asking the user to install the "bootkit"'s certificate into the UEFI trusted certificate store, since it is obviously not trusted by default). So it can't even be installed without clear warning to the user that something is wrong.

Come on, @dangoodin. I expect better than this from Ars, and I expect a correction, because this is just inexcusable misinformation. The original article clearly mentions how to kill this "unkillable" bootkit, which tells me you didn't even read the original article all the way.

A simple remedy tip to get rid of the bootkit is to move the legitimate /EFI/ubuntu/grubx64-real.efi file back to its original location, which is /EFI/ubuntu/grubx64.efi.

Update: article & headline have been updated.