Together AI· Inference platform

From 732 bytes to nowhere: shutting down Copy Fail in production

Summary We were able to get ahead of Copy Fail (CVE‑2026‑31431) by treating it as a fleet‑level emergency, shutting off the vulnerable crypto socket interface across our infrastructure within hours and rolling in kernel patches once they were stable in our AI workloads. Before upstream fixes were widely available, we relied on a targeted kernel hardening step: Unloading the vulnerable module and removing it from the module path so it could not be silently re-enabled. Copy Fail in one paragraph Copy Fail (CVE‑2026‑31431) is a logic bug in the Linux kernel’s crypto subsystem in the algif_aead AF_ALG interface used for AEAD operations. It gives any unprivileged local user a precise 4‑byte write primitive into the page cache of any readable file on the system. In practice, public exploits flip a few bytes in shared, setuid binaries in memory and ride that to root on mainstream Linux distributions. The on‑disk file never changes, and the page is never marked dirty, which means traditional file‑integrity checks don’t see the attack even as the modified binary runs. Why this matters for AI infrastructure On a developer laptop, Copy Fail is just a local privilege escalation. …

Announced

30 Apr 2026 00:00 UTC