Copy.Fail Linux Vulnerability - Schneier on Security

This is the worst Linux vulnerability in years. TL;DR copy.fail is a Linux kernel local privilege escalation, not a browser or clipboard attack. Disclosed by Theori on 29 April 2026 with a working PoC. It abuses the kernel crypto API (AF_ALG sockets) plus splice() to write four bytes at a time straight into the page cache of a file the attacker does not own. The exploit works unmodified across Ubuntu, RHEL, Debian, SUSE, Amazon Linux, Fedora and most others. No race condition, no per-distro offsets. The file on disk is never modified. AIDE, Tripwire and checksum-based monitoring see nothing. ...

Raccontata daschneier.com