🏗️🔧：keep the branch under review off the runner - #1820
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A semgrep audit rule flagged this workflow for checking out code from the incoming pull request. It does not: the ref was `github.event.pull_request.base.ref`, the base branch. The rule matches any ref beginning `github.event.pull_request`, so it cannot tell the base from the head. The finding was still worth acting on. The branch under review was fetched so its commit messages could be read, which put a stranger's objects on a runner holding credentials that can write here, with nothing but a comment to stop a later step executing them. Those messages now come from the API, so nothing of the branch arrives at all, and the checkout takes the default rather than naming a ref that reads like the wrong one. The token is no longer left in .git/config either. Nothing here pushes. Signed-off-by: Derek Lewis <DerekNonGeneric@inf.is> Assisted-by: Claude-Code:claude-opus-5
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From the semgrep audit finding on
commit-queue.yml:40.The finding's literal claim is wrong
The rule says the workflow "checks out code from the incoming pull request". It does not — the ref was
github.event.pull_request.base.ref, the base branch. Reading the rule shows why it fired anyway:github.event.pull_request ...matches any continuation, so.base.refand.head.refare the same to it.It was still worth acting on
The workflow fetched the branch under review —
git fetch origin pull/N/head— so its commit messages could be read. That put a stranger's objects on a runner holding credentials that can write to this repository, with nothing preventing a later step from executing them except a comment saying not to. Comments do not enforce anything, and the next person to add a build step here would not necessarily read it.So the mechanism is gone rather than the warning silenced:
GET /pulls/{n}/commitsreturns them oldest first, merges filtered out — so nothing from the branch reaches the runner at all.ref:on the checkout. For this event the default is already the base branch, and naming it explicitly was indistinguishable, to a reader and to a scanner, from naming the wrong one.fetch-depth: 0, since no range is computed locally any more.persist-credentials: false, because nothing here pushes and a token in.git/configis one more thing to pick up.The rule's precondition no longer holds — there is no
actions/checkoutwith aref— so the finding clears legitimately rather than by suppression.Verification
nps test— 16/16 tasks, 63/63 testsref:in the workflow is in a comment explaining its absence