Preface: Quite a lot of UEFI vulnerabilities and hardware misconfigurations have been found in past. This is an alert signal. As a matter of fact, the problem is that it’s very difficult to get malicious code into UEFI systems.
Background: Reading the first sector from a disk and loading it to 0x7C00 is a BIOS specific booting protocol. But it never been use. It is a old technology. UEFI bootloaders are loaded from a filesystem. UEFI requires the firmware and operating system loader (or kernel) to be size-matched; for example, a 64-bit UEFI firmware implementation can load only a 64-bit operating system (OS) boot loader or kernel.
Synopsis: A local attacker with access to system memory may exploit the UEFI vulnerability attack. Perhaps this is not the only way.
Dell mitigates design flaws in a specific product (Inspiron 5675). Please refer to the link below. https://www.dell.com/support/kbdoc/zh-hk/000180645/dsa-2020-247-dell-client-platform-security-update-for-uefi-bios-runtimeservices-overwrite-vulnerability