A new side-channel attack impacting multiple generations of Intel CPUs has been discovered, allowing data to be leaked through the EFLAGS register. The attack works as a side channel to Meltdown, a critical security flaw discovered in 2018, impacting many x86-based microprocessors. The attack is carried out in two phases, the first being to trigger transient execution and encode secret data through the EFLAGS register, and the second is to measure the execution time of the KCC instruction to decode the data. The researchers note that this timing attack isn’t as reliable as cache-state side-channel methods, and to get better results in recent chips, the attack would have to be repeated thousands of times.