Copy Fail: Public PoC and Full Details Disclosed for the 732-Byte Linux Root Exploit (CVE-2026-31431)

**Copy Fail (CVE-2026-31431):** A critical logic bug in the Linux kernel's AF_ALG AEAD implementation allows an unprivileged local attacker to perform a deterministic 4-byte write into the page cache of any readable file, enabling trivial setuid binary tampering and immediate root escalation; the proof-of-concept and full technical details are public, many distributions are affected since 2017, and administrators are advised to apply vendor patches or mitigate by blocking AF_ALG sockets (e.g., via seccomp).