MUTE: Pairwise Containment Tests for Shared State Leakage
Divyansh Agarwal · Team Mute
Submitted to AI Incident Response Sprint. Sprint projects are early-stage work by participants, not Apart Research publications.
MUTE tests a containment failure that ordinary sandbox evaluations can miss: separate AI-agent runs exchanging information through writable infrastructure they both legitimately access. It converts declared capabilities into a directed Shared Mutable Intersection graph, then tests predicted A-to-B paths using blinded 128-bit nonce challenges across separate writer and reader processes. In 32 trials per fixture, MUTE recovered 96/96 nonces across shared value, namespace, and post-exit residual-state fixtures, while recovering 0/32 in a tenant-scoped control and 0/128 reader-before-writer controls. It produces fail-closed, digest-bound evidence and reports only CHANNEL_DEMONSTRATED, NO_CHANNEL_OBSERVED, or INCONCLUSIVE. The current prototype uses synthetic local adapters and is intended for reproducible pairwise containment regression testing.
Reviews
Small tool that tests if two AI sandboxes are really separate, by trying to sneak a secret code between them. Simple, honest about its limits, does what it says. Would be nice to see it tested on something real next.
The motivation is clear and a good call out: evaluation runs are still mostly assessed one at a time, even when they share infrastructure. I'd push it further. As evals become more realistic to reduce eval awareness, they tend to share more infrastructure, not less. Leakage between runs also affects eval validity, since one run can contaminate another's results. The paper lists evaluation records as a shared resource but only treats them as a containment issue.
Recording negatives as "no channel observed" rather than "secure," and the reader-before-writer controls, are good design choices. But the contribution here is harder for me to identify. From my understanding, testing whether one tenant can write something another can read is standard isolation practice, and the capability graphs, blinded nonces and CI exit codes aren't new.
The perfect recovery rates are also expected on deterministic local fixtures. The authors acknowledge this is a self-consistency result, but it means the outcome was pre-determined by the design.
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Cite this project
@misc{agarwal2026mute,
title = {{MUTE: Pairwise Containment Tests for Shared State Leakage}},
author = {Divyansh Agarwal},
year = {2026},
month = sep,
note = {Submitted to AI Incident Response Sprint, an Apart Research Sprint},
howpublished = {\url{https://apartresearch.com/sprints/projects/mute-pairwise-containment-tests-for-shared-state-leakage-ti00}},
url = {https://apartresearch.com/sprints/projects/mute-pairwise-containment-tests-for-shared-state-leakage-ti00}
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