The mechanizable slice of CI supply-chain hardening, enforced at two points: at commit (the git hook, over staged changes) and at agent tool-use (over a tool call's arguments, as the agent writes) -- a workflow that references a third-party GitHub Action by a movable ref -- a branch or a version tag -- instead of a full 40-character commit SHA. A tag like v4 or a branch like main can be re-pointed at new code after review, so the action that runs tomorrow need not be the one that was audited ...
Installs into .claude/skills of the current project.
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---
name: pin-github-actions
description: "The mechanizable slice of CI supply-chain hardening, enforced at two points: at commit (the git hook, over staged changes) and at agent tool-use (over a tool call's arguments, as the agent writes) -- a workflow that references a third-party GitHub Action by a movable ref -- a branch or a version tag -- instead of a full 40-character commit SHA. A tag like v4 or a branch like main can be re-pointed at new code after review, so the action that runs tomorrow need not be the one that was audited today; a compromised or rug-pulled release rides in on exactly that mutability. The gate blocks an added line that references an action by a non-SHA ref (owner/repo at a tag/branch); a full 40-char SHA pin passes, local actions (no ref) pass, and 'pragma: allowlist unpinned-action' on the same line is a visible, deliberate exception. This is the OpenSSF Scorecard Pinned-Dependencies control for the slice a diff can show; signature and provenance verification stay out of scope."
metadata:
chock.artifact: hook
chock.enforcement: block
chock.coverage_without_chock: advisory
---
# Pin GitHub Actions
The mechanizable slice of CI supply-chain hardening, enforced at two points: at commit (the git hook, over staged changes) and at agent tool-use (over a tool call's arguments, as the agent writes) -- a workflow that references a third-party GitHub Action by a movable ref -- a branch or a version tag -- instead of a full 40-character commit SHA. A tag like v4 or a branch like main can be re-pointed at new code after review, so the action that runs tomorrow need not be the one that was audited today; a compromised or rug-pulled release rides in on exactly that mutability. The gate blocks an added line that references an action by a non-SHA ref (owner/repo at a tag/branch); a full 40-char SHA pin passes, local actions (no ref) pass, and 'pragma: allowlist unpinned-action' on the same line is a visible, deliberate exception. This is the OpenSSF Scorecard Pinned-Dependencies control for the slice a diff can show; signature and provenance verification stay out of scope.
```
on(commit|tool_use): block(content_regex) paths=.github/workflows/*|.github/actions/* scan=added_lines allowlist_pragma=pragma:\s*allowlist\s+unpinned-action content_pattern(regex)
Unpinned GitHub Action detected: a workflow references an action by a tag or branch (owner/repo at a movable ref) rather than a full 40-character commit SHA. Pin it to the SHA -- keep the version in a trailing comment for readability -- so a re-tagged or compromised release cannot change what runs. 'pragma: allowlist unpinned-action' on the same line marks a reviewed exception; in the agent (tool use, the turn's end) it counts only when that exact line is already committed in HEAD, so an agent asks a person rather than writing the pragma itself.
```
This skill is advisory: the client reading it has no mechanism to enforce it. The same policy compiled by `chock` blocks at commit, on an agent's file writes and at turn end. See https://github.com/open-coder-ai/chock
