# Transient Execution Wikipedia [page](https://en.wikipedia.org/wiki/Transient_execution_CPU_vulnerability): *Transient execution CPU vulnerabilities are vulnerabilities in a computer system in which a speculative execution optimization implemented in a microprocessor is exploited to leak secret data to an unauthorized party. The classic example is Spectre that gave its name to this kind of side-channel attack, but since January 2018 many different vulnerabilities have been identified.* - Contains a nice table outlining affected CPU architectures and mitigations ## Resources ### (Paper) A Systematic Evaluation of Transient Execution Attacks and Defenses ([abstract](https://www.usenix.org/conference/usenixsecurity19/presentation/canella), [pdf](https://www.usenix.org/system/files/sec19-canella.pdf)) Abstract: >Research on _transient execution_ attacks including Spectre and Meltdown showed that exception or branch misprediction events might leave secret-dependent traces in the CPU’s microarchitectural state. This observation led to a proliferation of new Spectre and Meltdown attack variants and even more ad-hoc defenses (e.g., microcode and software patches). Both the industry and academia are now focusing on finding effective defenses for known issues. However, we only have limited insight on residual attack surface and the completeness of the proposed defenses. > >In this paper, we present a systematization of transient execution attacks. Our systematization uncovers 6 (new) transient execution attacks that have been overlooked and not been investigated so far: 2 new exploitable Meltdown effects: Meltdown-PK (Protection Key Bypass) on Intel, and Meltdown-BND (Bounds Check Bypass) on Intel and AMD; and 4 new Spectre mistraining strategies. We evaluate the attacks in our classification tree through proof-of-concept implementations on 3 major CPU vendors (Intel, AMD, ARM). Our systematization yields a more complete picture of the attack surface and allows for a more systematic evaluation of defenses. Through this systematic evaluation, we discover that most defenses, including deployed ones, cannot fully mitigate all attack variants.