A denylist in front of /bin/sh is whack-a-mole. Measured 2026-09-18, end to
end through both screens: 5 of 11 named evasions ran with real effect - a
`command` prefix reached git, an escaped `rm` inside a shell fence deleted a
directory, `find -delete` deleted a file, `>|` and `tee` wrote outside the
working tree, a python one-liner deleted the whole tree - and 19 of 28 got
past the refusal list on its own. Every quoting, aliasing and indirection form
of the shell is another mole.
So the screen is now an ALLOWLIST. A criterion runs only when its first word
is a known test runner (npm test, npm run <script package.json declares>,
node --test, vitest, jest, pytest, python -m pytest, uv run pytest,
cargo test, go test, make test, bash <script under tests/>, a read-only git
subcommand) AND the command carries no shell operator and no newline.
Everything else is NOT RUN with the reason said out loud: never run, and never
reported as a failure either - an absent measurement is not a finding. That
also closes the smaller hole in the same file: a bare word a sentence merely
names (`whoami`, `login`, `package.json`) is no longer executed, because it is
not a runner.
REFUSED_BY_POLICY is gone with the list that produced it; a command outside
the allowlist is `unrunnable`, which in plan mode still fells the run and in
brief mode is reported to the reviewer as an absent measurement.
What the allowlist deliberately does NOT do, said in the file and in the
reviewer's rubric: it is not a sandbox. `npm test`, `npm run <script>` and
`make test` run whatever the repo's own package.json/Makefile says they run,
including a script that pushes - that is the repo's responsibility. And it
rejects honest commands too: an env prefix, a project's own binary, anything
piped. A check that needs one of those is declared through
`bash tests/<script>.sh`, the documented way in.
Red first: 6 of the new tests fail against the previous runner (measured with
an always-allow shim so the module still loads), including the end-to-end one
where the canary directory was deleted and files were written outside the
tree. The fixtures move from `true`/`false` to two allowlisted shell fixtures,
because `false` is no longer a runner - the fail case must still be a real
non-zero exit, not an unrun criterion.
Suite 1148 (1146/0/2).
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Kjell Tore Guttormsen
02243c6365