vault-secrets-webhook

packaged by Chainguard

Chainguard Container for vault-secrets-webhook

Bank-Vaults' mutating webhook, which injects secrets from HashiCorp Vault into Pod environments, and resolves vault: references in Secrets and ConfigMaps.

Chainguard Containers are regularly-updated, secure-by-default container images.

Download this Container Image

For those with access, this container image is available on cgr.dev:

docker pull cgr.dev/ORGANIZATION/vault-secrets-webhook:latest

Be sure to replace the ORGANIZATION placeholder with the name used for your organization's private repository within the Chainguard Registry.

Compatibility Notes

The Chainguard vault-secrets-webhook image is a drop-in replacement for the upstream ghcr.io/bank-vaults/vault-secrets-webhook image, with two differences.

The binary is at /usr/bin/vault-secrets-webhook rather than /usr/local/bin/vault-secrets-webhook. The entrypoint is the bare binary name and resolves through PATH, so the Helm chart and any default deployment are unaffected. Only a deployment that overrides command with the absolute upstream path needs updating.

This image has no shell or package manager, where upstream is Alpine based. That keeps the attack surface and image size down. If you rely on kubectl exec into the webhook pod, use the -dev variant, which adds a shell and apk.

The webhook runs as uid 65534, matching upstream and the chart's securityContext.runAsUser.

Prerequisites

A Kubernetes cluster and a reachable HashiCorp Vault. The webhook resolves vault: references at admission time, so it needs credentials for Vault itself when mutating Secrets and ConfigMaps.

Mutated Pods additionally pull a second image, vault-env, which fetches the secrets at container startup. It is set by vaultEnv.repository in the chart and defaults to ghcr.io/bank-vaults/vault-env; there is no Chainguard build of it yet.

Getting Started

The upstream Helm chart at oci://ghcr.io/bank-vaults/helm-charts/vault-secrets-webhook deploys the webhook. Override image.repository through a values.yaml:

image:
  repository: cgr.dev/ORGANIZATION/vault-secrets-webhook
  tag: latest

helm install vault-secrets-webhook \
  oci://ghcr.io/bank-vaults/helm-charts/vault-secrets-webhook \
  --namespace vault-secrets-webhook --create-namespace --wait \
  -f values.yaml

The chart generates its own CA and serving certificate by default (certificate.generate), so cert-manager is not required.

Injecting a secret into a Pod

Reference the secret with a vault: prefix in a container's environment:

apiVersion: v1
kind: Pod
metadata:
  name: app
spec:
  containers:
    - name: app
      image: cgr.dev/ORGANIZATION/wolfi-base:latest
      command: ["/bin/sh"]
      args: ["-c", "echo $APP_PASSWORD"]
      env:
        - name: APP_PASSWORD
          value: "vault:secret/data/webapp/config#password"

At admission the webhook rewrites the Pod rather than resolving anything itself. It adds a copy-vault-env init container that stages the vault-env binary onto a shared volume, replaces the container's entrypoint with that binary, and moves the original entrypoint into the arguments. The vault: reference is left untouched in the manifest.

At container startup vault-env reads the reference, fetches the value from Vault, and then execs the original entrypoint with the resolved value in its environment, replacing itself in the process. The secret therefore only ever exists in the running container's environment: it is never written back to the Pod object, the API server, or etcd.

Injecting into a Secret or ConfigMap

Secrets and ConfigMaps work differently. Here the webhook resolves the reference itself at admission and writes the value into the object, so what Kubernetes stores is the resolved secret, not the reference:

apiVersion: v1
kind: Secret
metadata:
  name: webapp
stringData:
  password: "vault:secret/data/webapp/config#password"

The resolved value is persisted in etcd like any other Secret, which means it is only as protected as the cluster's encryption at rest and RBAC. Prefer the Pod path when you would rather the secret never leave the container it is destined for.

ConfigMap mutation is off by default because it interferes with Helm; enable it with configMapMutation=true.

Configuration

The webhook reads its Vault settings from environment variables on the Deployment (env in the chart) and from per-object annotations.

Set VAULT_ADDR on the Deployment rather than relying on a vault.security.banzaicloud.io/vault-addr annotation. Since v1.23.1 an address supplied by an annotation is checked against an allowlist before anything else, so an in-cluster Service address is rejected unless it is listed in VAULT_ADDR_ALLOWLIST. Configuring the address operator-side avoids that entirely and keeps the decision with the cluster administrator rather than the workload:

env:
  VAULT_ADDR: http://vault.vault.svc:8200

Documentation and Resources

• Upstream vault-secrets-webhook documentation
• Mutating webhook configuration reference
• HashiCorp Vault documentation
• Chainguard Academy

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