meltdown

Definition

A CPU vulnerability disclosed in 2018 that lets an unprivileged process read kernel memory it should never see. Out-of-order execution acts briefly on the loaded value before the permission fault retires it, and the value's imprint on the cache survives and is recovered by timing. Unlike Spectre, Meltdown is closable in software: separating kernel and user page tables fixes it, at some syscall cost.