Apple hasn't disclosed exactly what security issues are addressed by iOS 11.2.2, but we can expect to see details on Apple's security page shortly.
iOS 11.2.2 and a supplemental update for macOS High Sierra 10.13.2 have been released with that exact aim in mind.
For those technically minded, you can review the details of the security flaw that effects nearly all modern processors, over at Google's Project Zero blog.More news: USA blocks $255 million military aid to Pakistan
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iOS 11.2.2 for iPhone and iPad contains security fixes that aren't fully fleshed out, but Apple does say that they affect Safari and Webkit to "mitigate the effects of Spectre". The download is now available from the App Store under "Updates".
Companies are in disagreement over the precise impact of the workarounds required to protect systems from the Meltdown and Spectre speculative execution flaws revealed earlier this month, with some pointing to a doubling of CPU time in their workloads while others claim to have seen 'negligible impact'.