Well, the bug in this specific case (based on the article by Tavis O. linked elsewhere in comments) looks to be the regular kind -- probably an off-by-one in a

Well, the bug in this specific case (based on the article by Tavis O. linked elsewhere in comments) looks to be the regular kind -- probably an off-by-one in a microcode edge case. That is, here it's not the case that the CPU functions correctly but leaves behind traces of things that should be private in timing side channels, as was the case for Spectre.