[Snoozus]

thank you for this, I have a follow up question: Now an attacker can not install an old, vulnerable version. But couldn't they just install a new, vulnerable version? Is there something that enforces encryption key deletion in one case and not the other?

[jeroenhd]

AFAIK the signature mechanism hasn't been defeated, so the attacker can only load software signed by the factory keys.

Which includes old, vulnerable versions and all patched, newer versions. By burning in the minimum version, the old code now refuses to boot before it can be exploited.

This is standard practice for low-level bootloader attacks against things like consoles and some other phone brands.