Security flaw in ‘nearly all’ modern PCs and Macs exposes encrypted data

I suppose the original article is https://press.f-secure.com/2018/09/13/firmware-weakness-in-m...

But even that is very light on details:

The attack exploits the fact that the firmware settings governing the behavior of the boot process are not protected against manipulation by a physical attacker. Using a simple hardware tool, an attacker can rewrite the non-volatile memory chip that contains these settings, disable memory overwriting, and enable booting from external devices. The cold boot attack can then be carried out by booting a special program off a USB stick

I suppose they attach something JTAG?