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Sprint projectSep 14, 2026San Jose, CA, USA

Watchlines and Muster: Executable Counterfactuals for Cyber Defense

Bobby Faber · Team Bobby Faber with a little help

Submitted to AI Incident Response Sprint. Sprint projects are early-stage work by participants, not Apart Research publications.

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Report: Watchlines and Muster: Executable Counterfactuals for Cyber Defense

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Concepts for reasoning about Cyber Defense: Watchlines

And a modest harness for testing counterfactuals against them: Muster.

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  1. I liked the focus on what remains compromised after a control works. The example where isolation interrupts the evidence needed for later revocation makes that point well.

    It is also good that the report acknowledges when a simple dependency graph gives the same answer. I would align the README with the implemented scenario and test a few alternative attack paths. That would help show how much the conclusions depend on the chosen reconstruction, which the report already recognizes as a limitation.

  2. High clarity tool for testing "if defense is placed here, how does it change attacker capabilities". At this time it only replays attack paths.

    Couple of recommendations/extensions:

    1. Turn into an interactive website for rapid demonstration of the incidents and what controls help with
    2. Potentially enrich the story with failed attempts, denied actions, rejected tool calls, blocked network requests (alternate branches/negative evidence). Informs what is not available.
    3. Leverage same failed attempts (even if synthetic) to also create counterfactual branches, then add plausible alternative branches to see if Watchline still holds

    Nice work!

  3. I think this project makes a useful distinction between stopping an attacker’s next action and removing access they already gained. It replays incident records with proposed defenses to explore how the outcome might change. One example shows how isolating a system early could leave investigators without information needed to remove that access later.

    I would treat this as a useful way to examine response decisions, rather than evidence that early isolation generally makes incidents worse. The result depends on assumptions about when defenses act and what information remains available afterward. Those assumptions need to be clear and consistent, particularly where the paper and repository describe access differently. The example raises a worthwhile question, but broader recommendations need evidence beyond this particular replay.

Cite this project

@misc{faber2026watchlines,
  title = {{Watchlines and Muster: Executable Counterfactuals for Cyber Defense}},
  author = {Bobby Faber},
  year = {2026},
  month = sep,
  note = {Submitted to AI Incident Response Sprint, an Apart Research Sprint},
  howpublished = {\url{https://apartresearch.com/sprints/projects/watchlines-and-muster-executable-counterfactuals-for-cyber-defense-uf3j}},
  url = {https://apartresearch.com/sprints/projects/watchlines-and-muster-executable-counterfactuals-for-cyber-defense-uf3j}
}

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