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

Copy Fail (CVE‑2026‑31431) is a significant vulnerability in the Linux kernel's crypto subsystem that allows unprivileged users to execute a precise 4-byte write into the page cache of any readable file, potentially leading to privilege escalation on mainstream Linux distributions. This vulnerability poses a high risk in AI infrastructures, where multi-tenant GPU nodes and CI jobs are common, as it can allow container compromises to escalate to root access on the host, potentially corrupting binaries or libraries shared by other tenants. To mitigate this, Together AI quickly disabled the vulnerable algif_aead interface across their infrastructure, employing kernel hardening techniques, and set up compliance checks to ensure ongoing security even if vulnerable kernels were rebooted. They plan to roll out vendor patches once available, prioritizing non-production clusters for testing, and maintain the algif_aead module disabled in environments that do not require it. This incident highlights the importance of a cautious approach to kernel exposure in shared environments and the need for robust monitoring to detect unusual activities indicative of such exploits.