Zizmor is a new tool to check your GitHub action workflows for security concerns. I found it really helpful to lock down actions.

Action workflows can be esoteric, and continuous integration is not everyone’s top concern, so it’s easy for them to have subtle flaws. A tool like zizmor is great for drawing attention to them.

When I ran it, I had a few issues to fix:

• Some data available to actions is manipulable by unknown people, so you have to avoid interpolating it directly into shell commands. For example, you might want to add the branch name to the action summary:

  - name: "Summarize"
    run: |
      echo "### From branch ${{ github.ref }}" >> $GITHUB_STEP_SUMMARY
  

  But github.ref is a branch name chosen by the author of the pull request. It could have a shell injection which could let an attacker exfiltrate secrets. Instead, put the value into an environment variable, then use it to interpolate:

  - name: "Summarize"
    env:
      REF: ${{ github.ref }}
    run: |
      echo "### From branch ${REF}" >> $GITHUB_STEP_SUMMARY
  

• The actions/checkout step should avoid persisting credentials:

  - name: "Check out the repo"
    uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
    with:
      persist-credentials: false
  

• In steps where I was pushing to GitHub, this meant I needed to explicitly set a remote URL with credentials:

  - name: "Push digests to pages"
    env:
      GITHUB_TOKEN: ${{ secrets.token }}
    run: |
      git config user.name nedbat
      git config user.email ned@nedbatchelder.com
      git remote set-url origin https://x-access-token:${GITHUB_TOKEN}@github.com/${GITHUB_REPOSITORY}.git
  

There were some other things that were easy to fix, and of course, you might have other issues. One improvement to zizmor: it could link to explanations of how to fix the problems it finds, but it wasn’t hard to find resources, like GitHub’s Security hardening for GitHub Actions.

William Woodruff is zizmor’s author. He was incredibly responsive when I had problems or questions about using zizmor. If you hit a snag, write an issue. It will be a good experience.

If you are like me, you have repos lying around that you don’t think about much. These are a special concern, because their actions could be years old, and not well maintained. These dusty corners could be a good vector for an attack. So I wanted to check all of my repos.

With Claude’s help I wrote a shell script to find all git repos I own and run zizmor on them. It checks the owner of the repo because my drive is littered with git repos I have no control over:

#!/bin/bash
# zizmor-repos.sh

echo "Looking for workflows in repos owned by: $*"

# Find all git repositories in current directory and subdirectories
find . \
    -type d \( \
        -name "Library" \
        -o -name "node_modules" \
        -o -name "venv" \
        -o -name ".venv" \
        -o -name "__pycache__" \
    \) -prune \
    -o -type d -name ".git" -print 2>/dev/null \
| while read gitdir; do
    # Get the repository directory (parent of .git)
    repo_dir="$(dirname "$gitdir")"

    # Check if .github/workflows exists
    if [ -d "${repo_dir}/.github/workflows" ]; then
        # Get the GitHub remote URL
        remote_url=$(git -C "$repo_dir" remote get-url origin)

        # Check if it's our repository
        # Handle both HTTPS and SSH URL formats
        for owner in $*; do
            if echo "$remote_url" | grep -q "github.com[/:]$owner/"; then
                echo ""
                echo "Found workflows in $owner repository: $repo_dir"
                ~/.cargo/bin/zizmor "$repo_dir/.github/workflows"
            fi
        done
    fi
done

After fixing issues, it’s very satisfying to see:

% zizmor-repos.sh nedbat BostonPython
Looking for workflows in repos owned by: nedbat BostonPython

Found workflows in nedbat repository: ./web/stellated
🌈 completed ping-nedbat.yml
No findings to report. Good job!

Found workflows in nedbat repository: ./web/nedbat_nedbat
🌈 completed build.yml
No findings to report. Good job!

Found workflows in nedbat repository: ./scriv
🌈 completed tests.yml
No findings to report. Good job!

Found workflows in nedbat repository: ./lab/gh-action-tests
🌈 completed matrix-play.yml
No findings to report. Good job!

Found workflows in nedbat repository: ./aptus/trunk
🌈 completed kit.yml
No findings to report. Good job!

Found workflows in nedbat repository: ./cog
🌈 completed ci.yml
No findings to report. Good job!

Found workflows in nedbat repository: ./dinghy/nedbat
🌈 completed test.yml
🌈 completed daily-digest.yml
🌈 completed docs.yml
No findings to report. Good job!

Found workflows in nedbat repository: ./dinghy/sample
🌈 completed daily-digest.yml
No findings to report. Good job!

Found workflows in nedbat repository: ./coverage/badge-samples
🌈 completed samples.yml
No findings to report. Good job!

Found workflows in nedbat repository: ./coverage/django_coverage_plugin
🌈 completed tests.yml
No findings to report. Good job!

Found workflows in nedbat repository: ./coverage/trunk
🌈 completed dependency-review.yml
🌈 completed publish.yml
🌈 completed codeql-analysis.yml
🌈 completed quality.yml
🌈 completed kit.yml
🌈 completed python-nightly.yml
🌈 completed coverage.yml
🌈 completed testsuite.yml
No findings to report. Good job!

Found workflows in BostonPython repository: ./bospy/about
🌈 completed past-events.yml
No findings to report. Good job!

Nice.