Hey everyone, A few days ago, a friend sent me a sample with the message: "IDA is going nuts on this, but it runs fine." That kicked off a deep dive that ended up revealing a massive blind spot across the entire RE industry.

TL;DR: Two opcodes from a 25-year-old Intel patent (0F 1A and 0F 1B) are valid NOPs that your disassembler probably can't see, making them perfect for anti-RE.

The Story: These opcodes were reserved by Intel in the 90s to allow new instructions to be added without breaking old software. On older CPUs, they'd just be NOPs. It was a brilliant idea. But somehow, tool developers for IDA, Ghidra, Binary Ninja, etc., just... missed a couple of them.

The result? IDA Pro sees db 0Fh, 1Ah... and stops analyzing the function. Ghidra marks it as undefined. You can literally break static analysis with a single, valid instruction that the CPU executes without a problem.

I've put together a full investigation, a PoC you can compile yourself, and a pre-compiled binary to test your own tools.

GitHub Repo with PoC & Research: https://github.com/sapdragon/hint-break

Full Article: https://alder-innocent-b3c.notion.site/THE-25-YEAR-OLD-INTEL...

Go ahead, throw patched.exe from the repo into your favorite tool and see for yourself. I'm curious to see what you all think.