Attackers can take control over a target’s computer and bypass all local security systems by abusing a hardware debugging interface included with Intel CPUs. The JTAG (Joint Test Action Group) is a debugging framework that has been included for many years with Intel chipsets. 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. In Skylake CPU line released in 2015, developers and engineers can access this powerful utility via common USB 3.0 ports, accessible from the device’s exterior.
Source: https://www.bleepingcomputer.com/news/hardware/intel-cpus-can-be-pwned-via-usb-port-and-debugging-interface/