Spectre
Spectre is a class of speculative-execution CPU vulnerabilities, first disclosed in 2017. When a processor mispredicts a branch, the work it does speculatively can leave traces in the cache, and an attacker can read private data back out of those traces with a timing attack.
Spectre logo, by Natascha Eibl (CC0, via Wikimedia Commons) 
How Spectre Variant 2 works, by User0116 (CC0, via Wikimedia Commons)