Apple just released iOS 11.2.2 with some Safari and WebKit improvements to mitigate the Spectre vulnerability. macOS is also receiving an update. It’s a supplemental update to macOS High Sierra 10.13.2 and it includes the same fix.
As always, you should update your devices with the latest security patches. In this case, Meltdown and Spectre are serious vulnerabilities. With Meltdown, a malicious application running on an unpatched device can read the unencrypted kernel memory. You don’t want anyone to grab your password and private encryption keys.
Meltdown was already addressed in previous updates. iOS 11.2, macOS 10.13.2 and tvOS 11.2 already included mitigations for Meltdown. Apple Watch chips aren’t affected by Meltdown.
On your iPhone or iPad, head over to the Settings app, then tap on General and Software Update. On your Mac, open the Mac App Store and check for updates.