Transient execution CPU vulnerability

Transient execution CPU vulnerabilities are vulnerabilities in which instructions, most often optimized using speculative execution, are executed temporarily by a microprocessor, without committing their results due to a misprediction or error, resulting in leaking secret data to an unauthorized party. The archetype is Spectre, and transient execution attacks like Spectre belong to the cache-attack category, one of several categories of side-channel attacks.

Source: Wikipedia — Transient execution CPU vulnerability (CC BY-SA 4.0)