The Spectre microarchitecture vulnerability has returned yet again, this time to vex just-in-time (JIT) engines that generate machine code for browsers, runtimes, and kernels. The vulnerability is found in many CPUs that use speculative execution, the process of executing code before it is called to boost performance. Researchers found speculative execution opens the door to side channel attacks through which secrets can be exposed or inferred. When news of that risk became known, chipmakers and OS developers scrambled to fix these vulnerabilities, which were referred to as Spectre and Meltdown. And since then, researchers have found two or three dozen variations, such as 2025's VMScape, one of several so-called "Spectre v2" attacks that attempt to exploit indirect branch prediction,…