Together AI Halts Copy Fail Exploit

Together AI has successfully neutralized a critical Linux kernel vulnerability, dubbed Copy Fail (CVE-2026-31431), which threatened its production AI infrastructure. The company acted swiftly, implementing a fleet-wide shutdown of the vulnerable crypto socket interface within hours of exploit details emerging.

Copy Fail is a logic bug within the Linux kernel's crypto subsystem, specifically the algif_aead AF_ALG interface. It grants unprivileged local users the ability to precisely overwrite 4 bytes in the page cache of any readable file. Publicly available exploits demonstrate how attackers can modify in-memory, setuid binaries to achieve root privileges without altering the on-disk file, bypassing traditional file integrity checks.

While a local privilege escalation on a developer's machine, this vulnerability presents a far graver threat in multi-tenant AI environments. A compromise within a container could escalate to root on the host, potentially corrupting data or binaries used by other tenants sharing the same kernel. This risk is amplified in cloud and AI platforms where containers are not considered a definitive security boundary.

Rapid Mitigation: Disabling algif_aead

Together AI's immediate response focused on eliminating the attack surface. As their production workloads do not rely on userspace algif_aead sockets, they were able to unload the vulnerable kernel module entirely. This effectively shut down the malicious code path without requiring a system reboot, a critical factor for long-running AI jobs.

To ensure the module could not be re-enabled, the module file itself was moved out of its standard directory. This approach provided a fast, low-risk, and durable mitigation, ensuring the vulnerability remained addressed even after host reboots. The company formalized this by encoding it as an idempotent compliance check within their configuration management.

A Path to Patched Kernels

Disabling the module was a crucial first step, but not the final solution. Together AI plans to adopt vendor-supplied kernel patches for CVE-2026-31431. Before widespread deployment, these patched kernels will undergo extensive testing in non-production clusters that mirror their most demanding AI workloads.

This includes performance testing, GPU driver compatibility checks, and stability assessments under real inference and training loads. Patches will then be rolled out incrementally by region and environment, prioritizing less shared clusters before moving to heavily multi-tenant ones. Even after patching, the company intends to keep algif_aead disabled in environments where it lacks a clear operational requirement, a strategy that reduces their overall kernel exposure.

This incident underscores the amplified impact of minor kernel bugs within dense, multi-tenant AI infrastructure. Together AI's experience reinforces the importance of a robust security posture, including default-off policies for niche interfaces, rapid fleet-wide response mechanisms, and rigorous validation pipelines to ensure security measures do not impede high-performance AI workloads. This approach to vulnerability mitigation in production is critical, much like the safety nets provided by technologies such as GitHub's eBPF Safety Net.