Introduction

A kernel local privilege escalation (LPE) vulnerability called "Copy Fail" (CVE-2026-31431) made the rounds. Social media and articles were full of "affected range is ≤6.19.12" and "run this command, and if it prints X you're vulnerable" — but deciding "we're vulnerable / safe" off a number and a one-liner felt wrong.

So instead of touching a production machine, I stood up a disposable VM carrying a pre-patch kernel , ran the official PoC for real, and felt with my own hands how easily root gets taken. Bottom line: a 732-byte Python one-shot took me from a non-root user to uid=0(root) , no race, 100% deterministic.…