I heard about the new ZombieLoad vulnerability. How do I protect my Mac?
For the official word, and how to mitigate the Intel issues on your Mac, see https://support.apple.com/en-us/HT210108

Realistically, if you've updated to macOS 10.14.5, use Safari as your web browser and only run applications downloaded from the App Store, you have nothing to worry about. Otherwise, you may want to review this link: https://support.apple.com/en-us/HT210119 

Apple has moved EXTREMELY quickly to handle this situation. Kudos to them!

I suspect Chrome, Firefox and other browsers will be updated soon. If you're extremely paranoid, you will need to disable hyperthreading (at a 40% performance hit).