Black & White Path

Jun 6, 2026 · Information Security

The Secret CPU Instructions Intel, AMD and ARM Keep Hidden (And Why They Matter)

The article explores the origins of undocumented CPU instructions—from early transistor‑saving tricks like SALC and POP CS to modern hidden backdoors such as Intel’s undocumented RISC core and the udbgrd/udbgwr commands—explaining how researchers like 0day_ninja use the MystFuzz tool to discover and exploit these covert opcodes.