Verifying Kubewarden

To verify the keyless-signed container images produced by the Kubewarden team, you can use the cosign CLI tool. For example, to verify the kubewarden/policy-server image, you can execute the following command:

You can then verify that the certificate in the returned JSON contains the correct issuer, subject, and github_workflow_repository extensions.

The same applies to all other images produced by the Kubewarden team, such as kubewarden/kubewarden-controller and kubewarden/audit-scanner.

All container images also have SBOM and provenance files that can be used to ensure the secure supply chain of the images. You can find attestation files on the release page of the component or attached to the container image in the OCI registry.

We use Docker to build the images and their attestations. However, the cosign command does not yet support the verification of the attestations generated by Docker from the OCI registry. For this reason, you need to download the files from the release page or the registry and verify them locally. If you want to download the attestation files from the OCI registry, you can follow the Docker documentation and use tools like crane or docker itself to download the files from the registry.

When downloading the tarball with attestation files from the release page of the Kubewarden components, extract them, verify the signature for the checksum file, and then check the attestation files:

Now that the files integrity is verified, you can inspect the SBOM and Provenance files.

You can find our Helm charts in our https:// traditional Helm repository under https://charts.kubewarden.io.

The same Helm charts are signed via Sigstore’s keyless signing, and pushed to an OCI repository that holds both the Helm chart and its provenance attestation as OCI artifacts.

Since Helm 3.8.0, Helm has support for OCI registries, but because of constraints in them, they can’t be searched via helm. You can find the list of charts in GitHub Container Registry.

To verify a Helm chart, you need cosign installed. Then execute the following command, for example:

You can then verify that the cert in the returned json contains the correct issuer, subject, and github_workflow_repository extensions.

The chart attestations are pushed to the OCI registry as an artifact layer. See the container images section on how to verify them.

Kubewarden charts ship imagelist.txt and (policylist.txt when relevant) inside of the chart. Hence, if you already verified the chart, you can use those lists to verify the consumed container images and policies.

Kubewarden also follows the usual practices with regards to Helm charts. Hence, one can also find all the images in the Helm charts with a plugin such as helm-image, or with the following script:

which gives us:

Now, for each image in that list you can verify their Sigstore signatures following the instructions from the previous section.

kwctl binaries are signed using Sigstore’s blog signing.

When you download a kwctl release each zip file contains two files that can be used for verification: kwctl.sig and kwctl.pem.

In order to verify kwctl you need cosign installed, and then execute the following command:

You can then verify that the cert in the returned json contains the correct issuer, subject, and github_workflow_repository extensions.

The SBOMs are signed and published in the GitHub Releases of the project.

The provenance attestation for kwctl is verified by using gh attestation verify. For example with gh attestation verify kwctl-linux-x86_64 --repo kubewarden/kwctl.

Policies maintained by the Kubewarden team are also signed using the Sigstore project. Similar to usual container images, one can verify them using cosign:

You can then verify that the cert in the returned json contains the correct issuer, subject, and github_workflow_repository extensions.