The GRUB2 upstream reintroduced CVE-2020-15705. This refers to a distro specific flaw which upstream introduced in Grub 2.05. If certificates that signed GRUB2 are installed into db, GRUB2 can be booted directly. It will then boot any kernel without signature validation. The booted kernel will think it was booted in Secure Boot mode and will implement lockdown, yet it could have been tampered. This flaw only affects upstream and distributions using the shim_lock verifier.