Packer adds SLSA provenance generation and verification for machine images

Packer v1.16.0 adds a native mechanism to generate SLSA-compliant provenance statements for every machine image it builds. The provenance includes cryptographic hashes of the source artifacts, the build command, and the environment that ran the build. Operators can later verify this metadata to confirm the image was produced from the expected inputs on a trusted build platform, rather than being tampered with or built from an undisclosed fork of the source code.

The feature is opt-in and requires no changes to existing templates, but enabling it means adding a new provenance block to the HCL2 configuration. Once enabled, Packer will emit a signed attestation alongside the image artifact. Verification is performed with standard SLSA tooling, so teams already using SLSA for other artifacts can reuse the same workflows and policies. The cost is a small increase in build time and storage for the additional metadata files.

Provenance verification stops working if the signing key is compromised or if the build platform is not itself SLSA-compliant. Teams must also ensure that every input to the build, including base images, provisioner scripts, and variable files, is itself verifiable, otherwise the provenance chain breaks at the first unverified link. The feature does not prevent malicious code from being included in the image; it only ensures that the code came from the declared sources.