A microcode (uCode) hot-upgrade method for bare metal cloud deployment and associated apparatus. Under the uCode hot-upgrade method, a uCode path is received at an out-of-band controller (e.g., baseboard management controller (BMC)) and buffered in a memory buffer in the out-of-band controller. The out-of-band controller exposes the memory buffer as a Memory-Mapped Input-Output (MMIO) range to a host CPU. A uCode upgrade interrupt service is triggered to upgrade uCode for one or more CPUs in a bare-metal cloud platform during runtime of a tenant host operating system (OS) using an out-of-bound process. This innovation enables cloud service providers to deploy uCode hot-patches to bare metal servers for live-patch without touching the tenant operating system environment.