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World C4: Pipeline Shields

SLSA levels and allow-lists

You will learn: how to prove where a build came from, and how to allow only trusted actions.

Checked with GitHub Actions 2026-10 on 31 Oct 2026

The problem

You pull ghcr.io/you/shop:1.2.0 to deploy it. Did your pipeline build it, or someone’s laptop? How can you tell?

Watch

A frozen pack has a label: which kitchen, which recipe, when. A build’s label is called provenance. When it is signed, nobody can quietly fake it. What does it tell you?

Drag a card into a box. Or tap the card, then tap the box.

      Watch

      SLSA: A food-safety grade for builds (say "salsa"): levels that show how much you can trust where a package was made. (say “salsa”) grades builds, like food-safety grades. Put its Build levels in order. Weakest at the top.

      Weakest at the top. Put these in order. Use the arrows, or drag.

      • L3: hardened builds, so runs cannot touch each other
      • L0: no promises
      • L1: provenance exists
      • L2: a hosted build platform signs it

      Predict

      Your GitHub Actions workflow makes an artifact attestation: a signed provenance record. Which SLSA Build level is that?

      Try it

      Check an image before you deploy it. Build the command.

      Tap the pieces in the right order.

      …

      Watch

      Big teams also keep an approved supplier list: an allow-list: The approved supplier list: only the actions on it may run in your organisation.. Only actions on it may run. Good rule, or risky?

      Swipe right for good, left for needs work. Or use the buttons.

      1 / 4

      Allow actions made by GitHub

      Try it

      Your allow-list must block one bad action, and keep everything else. Which entry does that?

      You did it!

      You can now prove where a build came from, and allow only trusted actions.

      Go deeper (optional)

      Where the story breaks: a food label sits on the pack. Provenance is a separate signed file. A tool checks it, not your eyes. And no grade says the recipe is good. SLSA 1.2 also adds a Source track, for trusting the code itself. Real rep: verify an image you pushed in World C2.