"Wow, we (+@h0t_max and @_Dmit) have found two undocumented x86 instructions in Intel CPUs which completely control microarchitectural state (yes, they can modify microcode)" https://twitter.com/_markel___/status/1373059797155778562
These instructions don't work if the CPU isn't in its service mode state. "Red unlocked" they call that state, I think? So this doesn't look like anything to worry about.
This seems more like more progress towards being able to reverse engineer Intel's microcode, rather than a security attack?