Attackers with access to a device can take control over a target's computer and bypass all local security systems by abusing a hardware debugging interface included with Intel CPUs, which in recent years has become accessible via an external USB 3.0 port.

The debugging interface is JTAG (Joint Test Action Group), a debugging framework that has been included for many years with Intel chipsets.

JTAG works under the software level, allowing engineers, developers, and system administrators access to a hardware debugging utility that can provide insight into how the OS kernel, hypervisors, and local drivers are performing.

[...] In older Intel CPUs, the JTAG interface was only accessible by connecting a special device to the ITP-XDP port found on the motherboard, inside a computer's chassis.

Starting with the Skylake CPU line released in 2015, Intel dropped the ITP-XDP interface and allowed developers and engineers to access this powerful debugging utility via common USB 3.0 ports, accessible from the device's exterior, via a new a new technology called Direct Connect Interface (DCI).

Two Positive Technologies security researchers, Maxim Goryachy and Mark Ermolov, argue that this has significantly simplified the attack procedure needed to take control of Intel-based machines.

The two explain that while most hardware vendors disable the DCI interface before they ship products out of the factory's gateway, the DCI interface can be re-enabled via a computer's BIOS settings.

If a target doesn't password-protect its BIOS, attackers can enable this setting, and then connect via USB and alter core processes, undetectable to any type of security software installed on a targetted[sic] machine.