As the chip vendors wrestle to get their arms around the Meltdown and Spectre vulnerabilities, we’re slowly determining the exposure of AMD and ARM to the exploit. Intel, unfortunately, is totally vulnerable. With AMD and ARM, though, it gets complicated.
First, let’s go over the Spectre exploit, which is a second class of attacks similar to Meltdown, the one we all know. Like Meltdown, Spectre exploits speculative execution in order to root out information from a CPU’s cache. Spectre is different because of how it runs.
While Meltdown is based on a specific implementation of speculative execution, Spectre exploits a risk to speculative execution that requires more work to exploit but is also considered harder to mitigate. Because it’s more obscure and arcane, it’s not as well understood. That’s why Meltdown is considered the bigger risk.
Source: NW Security 1