How to enable full mitigation for Microarchitectural Data Sampling (MDS) vulnerabilities on your Mac


What is Microarchitectural Data Sampling and how to enable it on your Mac?

Apple added Microarchitectural Data Sampling with security updates in macOS Mojave, High Sierra, and Sierra to protect against speculative execution vulnerabilities in Intel CPUs. With this security update, macOS fixes this issue for Safari with no measurable performance impact. Also this update stops exploitation of these vulnerabilities via JavaScript or as a result of redirecting to a malicious website in Safari.

The full mitigation that includes disabling hyper-threading, stops information leakage across threads and when transitioning between kernel and user space, which is associated with the MDS vulnerabilities for both local and web attacks. If you are using Mac running macOS Mojave, High Sierra, and Sierra, you may protect it by enabling full mitigation for Microarchitectural Data Sampling (MDS) vulnerabilities. Let’s learn how to do that.

If you want to enable full mitigation on your Mac, you need to start your Mac in macOS Recovery and then enter commands in the Terminal app. Follow these steps:

  • First of all, turn on or restart your Mac and immediately press and hold “Command ()-R” or any other macOS Recovery key shortcut on your keyboard.
  • Select “Terminal” from the Utilities menu in the menu bar.




  • In the Terminal prompt, enter the following two commands, one at a time and press “Return” after each one.
nvram boot-args="cwae=2"
nvram SMTDisable=%01
  • Finally, select “Restart” from the Apple menu.

In case you want to do disable the full mitigation for re-enabling hyper-threading, you may reset NVRAM and restart your Mac. Moreover, if you directly want to check if hyper-threading is enabled or disabled in the System Information app. Select Apple menu > About This Mac, then click the System Report button. Now select Hardware in the sidebar and check Hyper-Threading Technology is Enabled or Disabled. If this option is not there, it means your Mac does not support hyper-threading.

Now read: What is application firewall and how to configure it on Mac

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