Wikner and Razavi’s research found that even with the IBPB defense, Intel’s processors still allow branch predictions to be reused, leading to security leaks.

“We found a microcode bug in recent Intel microarchitectures, like Golden Cove and Raptor Cove, which retains branch predictions that should have been invalidated by the IBPB,” the researchers noted. “Such post-barrier speculation allows an attacker to bypass security boundaries imposed by process contexts and virtual machines.”

The duo found that this flaw affects several Intel processors, including 12th, 13th, and 14th generation Intel Core processors and 5th and 6th generation Intel Xeon processors. These processors were specifically designed to address the vulnerabilities identified in earlier Spectre variants, but this newly discovered bug allows attackers to bypass those security defenses​.