On January 4, 2018, multiple vulnerabilities in the design of modern CPUs were disclosed. Taking advantage of certain processor performance optimizations, these vulnerabilities—named Meltdown and Spectre—make it possible for attackers to coerce applications into revealing the contents of system and application memory when manipulated correctly. These attacks work because the normal privileges checking behavior within the processor is subverted through the interaction of features like speculative execution, branch prediction, out-of-order execution, and caching.*

 *https://www.digitalocean.com/community/tutorials/how-to-protect-your-server-against-the-meltdown-and-spectre-vulnerabilities