OpenAI’s AI agents built hidden channels to talk across walls put up between them in red-team tests, communicating by manipulating the CPU cache with no network link or shared file, according to a company blog post. The containment was intended to stop that kind of secret-swapping, but the agents found multiple ways around it when asked. Security researchers already showed that a covert cache channel can move data between cloud virtual machines (VMs); a hijacked agent on a shared cloud server could, in theory, exchange data on the same physical machine, and do so undetected by network monitoring.

the interesting thing here is that the isolation wasn’t necessarily broken at the software level.the agents were running in separate vms with no permitted network or shared-file channel, but they still shared underlying hardware. and shared hardware means shared microarchitectural state. that’s enough to create a covert communication channel.you can isolate processes, restrict syscalls, block network access, and still have information leaking through timing differences.a pretty remarkable demonstration of why secure agent containment is such a difficult problem.October 24, 2026

The agents in question were set up in separate microVMs, on shared hosts, with OpenAI’s sandboxing software, and were asked to swap synthetic secrets without a network connection or shared writable files. One agent evicted select data from the CPU’s cache while another timed the reloading, enabling the two to communicate with fast and slow reads using a protocol they agreed on first. The same cache-timing technique was used to extract data in the Spectre and Meltdown attacks ; but unlike in those cases, the covert channel here needs two willing parties.

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