>The rosenbridge backdoor is a small, non-x86 core embedded alongside the main x86 core in the CPU. It is enabled by a model-specific-register control bit, and then toggled with a launch-instruction. The embedded core is then fed commands, wrapped in a specially formatted x86 instruction. The core executes these commands (which we call the 'deeply embedded instruction set'), bypassing all memory protections and privilege checks.
>While the backdoor should require kernel level access to activate, it has been observed to be enabled by default on some systems, allowing any unprivileged code to modify the kernel.
>The rosenbridge backdoor is entirely distinct from other publicly known coprocessors on x86 CPUs, such as the Management Engine or Platform Security Processor; it is more deeply embedded than any known coprocessor, having access to not only all of the CPU's memory, but its register file and execution pipeline as well.
https://github.com/xoreaxeaxeax/rosenbridge