A weakness in the way addresses are speculated in the memory subsystem of Intel CPUs makes all manner of attacks much easier to pull off (archived). Particularly ROWHAMMER. This speculation weakness appears to be particular to Intel CPUs with AMD, ARM, and others not being weak in this specific way. Across Intel processors however, this weakness is endemic stretching all the way back to when Intel first started using the "Core" branding to label processor models.
Intel was reportedly informed of this defect in their products on December 1st. The fellows who sinfully waited 90 days later before going public would like for this property of Intel's late model CPUs to be dubbed SPOILER, an all caps name that in this case is not an acronym for anything.