yacosta738/agent-harness/pinned-tag

Pinned Tag Management Skill

Skill for managing "pinned tags" and commit SHAs, primarily for GitHub Actions security.

Overview

This skill helps locate and validate tags in remote repositories using git ls-remote --tags, resolving the specific commit SHA for a tag (including annotated tags), and providing patches to pin dependencies. It specifically targets GitHub Actions security best practices by encouraging the use of full commit SHAs instead of mutable tags.

When to Use

• You need to fix "Unpinned tag for a non-immutable Action in workflow" security alerts.
• You want to ensure reproducibility by pinning a GitHub Action or dependency to a specific commit

SHA.

• You need to verify if a tag exists before updating a manifest or CI workflow.

Critical Patterns

• Immutability for Actions: For GitHub Actions, always prefer the full 40-character commit SHA

over a tag name. Tags are mutable and can be moved, leading to security risks or broken builds.

• Annotated vs Lightweight Tags:
• Annotated Tags: git ls-remote returns two entries. The one ending in ^{} is the "

peeled" reference pointing directly to the commit object. ALWAYS use this one.

• Lightweight Tags: Return only one entry, which is the commit SHA.
• Selection Logic: When resolving, always sort the results and take the last one to ensure

^{} is preferred over the tag object SHA.

• Verification: Always verify the resolved SHA belongs to the expected tag before applying

changes.

Commands

1. Resolve Tag to SHA (GitHub Actions Friendly):

``bash # Example: Resolve 'v2' tag for actions/checkout # This command ensures that for annotated tags, the commit SHA (peeled tag ^{}) is selected # by sorting and taking the last entry (where ^{} alphabetically follows the base tag). git ls-remote --tags https://github.com/actions/checkout.git | rg "refs/tags/v2(\^\{\})?$" | sort | tail -n 1 | awk '{print $1}' ``

1. List all remote tags:

``bash git ls-remote --tags https://github.com/owner/repo.git ``

1. Check for specific tag existence:

``bash git ls-remote --tags https://github.com/owner/repo.git | rg "refs/tags/v1.2.3" ``

Workflow for GitHub Actions

1. Identify the Action: Find the uses: owner/repo@tag line in the workflow YAML.
2. Resolve SHA: Run git ls-remote --tags https://github.com/owner/repo.git filtered by the

tag.

1. Apply Patch: Replace the tag with the SHA and add the tag name as a comment for readability.

• Before: uses: actions/checkout@v3
• After: uses: actions/checkout@f43a0e5ff2bd294095638e18286ca9a3d1956744 # v3

Limitations

• Cannot access private repositories without proper credentials (SSH/Token).
• Some actions may not use standard semver tags; always double-check the remote refs.

Commit Policy

• This skill does NOT create commits automatically without explicit permission.
• Suggested commit message: sec(ci): pin <action-name> to commit SHA for immutability

Resources

• GitHub Security Best Practices for Actions
• Tools: git, rg, awk