Spectre bug is back, this time to haunt JIT engines

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.