Apple released security updates for macOS Sierra and OS X El Capitan that address the Meltdown and Spectre processor security flaws. Security Update 2018-001 Sierra and Security Update 2018-001 El Capitan also include the same general security fixes includes in macOS High Sierra 10.13.3, which was also released Tuesday.
Meltdown and Spectre are the names of security holes that could allow maliciously crafted software to access data that should be protected. In combination, both vulnerabilities compromise most computing devices released over the last ten years. Apple mitigated against them in iOS 11 and macOS High Sierra in earlier updates, and these two security patches catch up the previous two Mac operating systems.
The security updates are available through the Mac App Store’s Update function for Macs running Sierra and El Capitan.