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GitHub Actions Workflow Standards

GitHub Actions workflows operate in a highly privileged software supply chain environment. Workflows can access repository secrets, push code, create releases, publish packages, and interact with external services. A security weakness in a workflow file can have severe consequences.

WordPress uses two complementary linting tools to help maintain the quality and security of workflow files in the .github/workflows directory: Actionlint and Zizmor. This page documents the tools and how contributors should address errors or warnings that they report.

Actionlint

Actionlint is a static checker for workflow files. It focuses primarily on correctness: syntax validation, type checking for expressions, validation of inputs for actions and reusable workflows, syntax checking of shell scripts, and other common mistakes. See the Actionlint documentation for details.

Actionlint runs on pull requests and on pushes to the main branches on the wordpress-develop repo. It reports its findings as check results, just like the unit test and coding standards workflows. A failing Actionlint check must be fixed before the changes in the PR can be committed.

Zizmor

Zizmor is a security-focused linter for workflow files. It detects template injection vulnerabilities, excessive permissions, dangerous triggers, unpinned dependencies, credential persistence, and dozens of other security weaknesses. See the Zizmor documentation for details.

Zizmor also runs on pull requests and on pushes to the main branches on the wordpress-develop repo and reports its findings to GitHub Code Scanning. This means:

  • Results are available on the Security → Code Scanning tab of the repo for users with administrative permission on the repo.
  • Errors and warnings that are newly introduced in a pull request will cause the code scanning check to fail. A "Code scanning results" status check will report failures, with inline annotations on the affected file and line.
  • Existing issues act as a baseline and won't affect new pull requests until they are fixed or dismissed.

Running locally

If you're making changes to workflow files in the .github/workflows directory, you can run both linting tools locally before pushing. Actionlint and Zizmor are both available via package managers for all operating systems, as well as via Docker images.

Running Actionlint

From the root of the repository, run:

actionlint

Running Zizmor

From the root of the repository, run (note the trailing period):

zizmor .

To enable the online audits that check for known-vulnerable actions and impostor commits, you can use the gh CLI tool from GitHub to provide an auth token:

GH_TOKEN=$(gh auth token) zizmor .

Some findings that are reported locally may be suppressed in the repository's Code Scanning settings. If you encounter a locally reported finding that does not appear in Code Scanning results, check whether it has been dismissed.

Addressing common security issues

The following sections cover common findings and how to address them.

For full information about specific results from the linting tools, consult the Actionlint documentation and the Zizmor documentation.

Template injection

Template injection occurs when a GitHub Actions expression such as ${{ github.event.issue.title }} is used directly within a run: block. GitHub Actions expressions are interpreted prior to running the script, therefore an attacker who controls the expression value can inject arbitrary shell commands, regardless of whether the expression is wrapped in quotes.

Incorrect:

- name: Print title
  run: echo "Title: ${{ github.event.pull_request.title }}"

Correct:

- name: Print title
  env:
    PR_TITLE: ${{ github.event.pull_request.title }}
  run: echo "Title: ${PR_TITLE}"

When the value is passed through an environment variable, it is treated as data rather than code, preventing injection.

For actions/github-script steps, pass values through the env block and access them via process.env instead of using template expressions in the script body:

Incorrect:

- name: Print title
  uses: actions/github-script@...
  with:
    script: |
      const title = "${{ github.event.pull_request.title }}";

Correct:

- name: Print title
  env:
    PR_TITLE: ${{ github.event.pull_request.title }}
  uses: actions/github-script@...
  with:
    script: |
      const title = process.env.PR_TITLE;

Dangerous triggers

The pull_request_target and workflow_run triggers run in the context of the base repository and have access to repository secrets. If a workflow triggered by pull_request_target checks out the pull request's head ref and runs code from it, an attacker can execute arbitrary code with access to secrets.

  • Avoid pull_request_target or workflow_run unless your workflow genuinely needs access to repository secrets to operate on a pull request (for example, to comment on the PR or manage labels).
  • Never check out the pull request's head ref (github.event.pull_request.head.ref) in a pull_request_target workflow and then run code from that checkout.
  • If pull_request_target or workflow_run is necessary, document the justification inline with a comment explaining why the trigger is safe in context.

Excessive permissions

Workflow and job permissions should follow the principle of least privilege. Every workflow file should include a top-level permissions: {} block that grants no permissions, with individual jobs declaring only the specific permissions they need. Omitting a permissions declaration entirely is not sufficient.

Incorrect:

permissions:
  contents: write

jobs:
  lint:
    # This job only reads code, it doesn't need write access.
    runs-on: ubuntu-latest

Correct:

permissions: {}

jobs:
  lint:
    runs-on: ubuntu-latest
    permissions:
      contents: read

Git credential persistence

The actions/checkout action persists credentials by default so that subsequent git operations can authenticate. If the checkout directory is later uploaded as an artifact (or its contents are otherwise exposed), the persisted credentials can be leaked.

Always set persist-credentials: false on actions/checkout unless subsequent steps in the same job genuinely need to perform authenticated git operations (such as pushing commits).

Correct:

- uses: actions/checkout@...
  with:
    persist-credentials: false

If the job needs persistent credentials (for example, to push built files), set persist-credentials: true explicitly so the intent is clear and auditable, and include an accompanying comment.

This credential persistence risk is often referred to as "artipacked", and Zizmor uses this name for its corresponding audit.

GitHub environment manipulation

Writing to $GITHUB_ENV or $GITHUB_PATH from a shell script is dangerous if the input is user-controlled, because an attacker can inject arbitrary environment variables or prepend to PATH.

  • To pass state between steps, prefer writing to $GITHUB_OUTPUT instead. Unlike $GITHUB_ENV and $GITHUB_PATH, outputs are not injected into the environment or PATH of subsequent steps.
  • If you must write to $GITHUB_ENV or $GITHUB_PATH, only write values that are fully controlled by the workflow, not with values derived from pull request content, issue bodies, commit messages, or other user-controllable inputs.
  • If you must process user-controllable input, validate and sanitize it before writing to these files.

Unpinned uses

All third-party actions must be pinned to a full commit SHA, not a tag, branch, or floating version reference such as v6. Tags can be moved or deleted as well as added, meaning a tagged reference could silently point to different (potentially malicious) code in the future.

Incorrect:

- uses: actions/checkout@v6

Correct:

- uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2

Always include a comment after the SHA that includes the exact name of the pinned tag, for example v6.0.. A floating value such as v6 is not sufficient. When updating an action, update both the SHA and the version comment.

Cache poisoning

Using GitHub Actions caching in workflows that produce release artifacts is risky. It's possible for a cache to be poisoned by an attacker in a separate workflow, allowing the poisoned cache to inject malicious content into a release.

An attacker with access to a valid GITHUB_TOKEN can poison the repository's GitHub Actions caches. Combined with the default behaviour of actions/cache during cache restoration, an attacker's payload can be retrieved from the poisoned entry and executed at workflow runtime, potentially compromising the package or release artifact that's about to be published.

Do not use actions/cache or the built-in caching features of other actions in workflows that build or publish packages or release artifacts.