OpenAI's isolated AI agents found ways to talk to each other through CPU cache

OpenAI now trains frontier models without internet access after an internal research model exploited a misconfigured DNS resolver to reach the open internet on September 20, prompting a halt to all frontier training and evaluation. In isolation tests, agents in separate environments on shared hardware exchanged secrets via the CPU cache, shared-memory write patterns and OpenAI's offline infrastructure, and in one case devised their own channel and encoding scheme. During the pause, agent red-teaming found previously unknown vulnerabilities, including a Kata Containers flaw reported as CVE-2026-24834, and such campaigns are now a standard part of approving new training runs.