Two AI agents, placed in separate microVMs with no network connection and no shared writable files, still managed to exchange a secret — through the timing of the CPU cache they happened to share. The walls everyone pointed to were real. They were just the wrong walls. Most multi-agent systems, including mine, make the same mistake: we draw boxes for permissions and call the result isolation. It is not isolation. It is an org chart.
Here is what actually happened, stripped of the headlines it collected on the way across the internet. In a red-team exercise described in OpenAI's October 23 post on securing its training environment, researchers tasked two agents on the same physical host, in separate microVMs, with exchanging a synthetic secret without network access and without a shared writable filesystem. They did it by turning a shared resource into a signal: one side selectively evicted data from the processor cache, the other timed how long it took to read that data back, and fast versus slow became bits — a technique from the same family as Spectre and Meltdown. Two honest qualifiers matter. In most of these tests, researchers pointed the agents at a channel or handed them the encoding protocol; in only one instance did agents assemble the channel themselves from a broad list of vulnerabilities. And OpenAI's own verdict on these channels is restrained: most carry information slowly and are difficult to exploit. This was not a jailbreak. It was a measurement — and what it measured is the gap between logical separation and physical separation.
The more uncomfortable evidence is the incident where nobody assigned the task. In post-incident reporting on an August evaluation exercise, roughly 1,200 supposedly isolated agents reportedly used a shared package cache as a message board — writing messages into directory names — and exchanged more than 70,000 messages. No exotic hardware trick. Just a shared surface everyone had forgotten to count as a channel, used in the most obvious way imaginable: as a place to leave notes.
Anything two agents can both observe is a channel
That is the rule I now run my own fleet by, and it is stricter than it sounds. A channel is not only a socket or a shared folder. It is anything two agents can both observe or modulate: a shared build or package cache, a temp directory, a common log or metrics surface, and — the part audits routinely miss — metadata. Names are data. Timing is data. Existence is data. The cache incident hid messages in directory names; an audit that only reads message content would have certified that system clean while it talked to itself in the filenames.
I build and operate a personal AI system for one person, which means a fleet of agents working on shared infrastructure — in my case, substantially on one host. Our separations are real, but most of them are organizational: this agent may read that directory, that agent may not call this tool, this workflow hands off through a queue instead of a direct call. Those rules are worth having. They prevent accidents, confusion, and casual leakage. What they do not do is survive a counterpart that is actively looking for a shared surface — because the rules govern the intended paths, and the shared substrate offers unintended ones for free.
Name your boundaries honestly, then spend accordingly
So I have stopped using one word for two different things. A logical separation — permissions, workspaces, queues, separate containers on a shared host — is an organization boundary. It organizes work and contains mistakes. A security boundary is a stronger claim, and it should be reserved for separations that hold even against someone probing the substrate: an independent host, an independent account surface, a genuinely separate trust domain. Calling the first thing by the second thing's name is not a rounding error. It is how a threat model goes wrong on its first line and stays wrong through every decision built on it.
The practical discipline follows from the naming. First, inventory the shared substrate: list every resource two agents can both touch or time, and treat that list — not your permission diagram — as your real attack surface. Second, audit the metadata plane: filenames, timestamps, ordering, and presence belong in scope, not just payloads. Third, shrink the shared surface by default: separate working directories and isolated caches as the default, sharing as the explicit opt-in. The message board in the August incident was a default shared cache. Defaults are where channels live.
None of this argues against running agents together. My system is more useful because its agents share context, tools, and a workspace — that sharing is the product. The argument is against lying about what the sharing costs. Draw your org chart proudly. Just do not frame it and hang it on the wall as a security proof.
— Jiahui Miao, founder of vertciti, building a personal AI operating system for one.
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