gcloud-gke-client-certificate-enabled: GKE Clusters With Client Certificate Authentication Enabled

id: gcloud-gke-client-certificate-enabled

info:
  name: GKE Clusters With Client Certificate Authentication Enabled
  author: princechaddha
  severity: medium
  description: |
    Ensure that authentication using client certificates is disabled for your Google Kubernetes Engine (GKE) clusters. Client certificates require manual key rotation for authentication and are difficult to revoke. It is highly recommended to use alternative authentication methods like OpenID Connect, which is the default authentication method used by gcloud and handles token management automatically.
  impact: |
    Using client certificate authentication introduces security management challenges as certificates don't auto-rotate and are difficult to revoke, potentially leading to security risks if certificates are compromised or not properly rotated.
  remediation: |
    Re-create your clusters without client certificates using:
    gcloud container clusters create NEW_CLUSTER_NAME --no-issue-client-certificate
  reference:
    - https://cloud.google.com/kubernetes-engine/docs/how-to/hardening-your-cluster
    - https://www.trendmicro.com/cloudoneconformity/knowledge-base/gcp/GKE/disable-client-certificate.html
  tags: cloud,devops,gcp,gcloud,gke,kubernetes,security,authentication,gcp-cloud-config

flow: |
  code(1)
  for(let projectId of iterate(template.projectIds)){
    set("projectId", projectId)
    code(2)
    for(let cluster of iterate(template.clusters)){
      cluster = JSON.parse(cluster)
      set("clusterName", cluster.name)
      set("location", cluster.location)
      code(3)
    }
  }

self-contained: true

code:
  - engine:
      - sh
      - bash
    source: |
      gcloud projects list --format="json(projectId)"

    extractors:
      - type: json
        name: projectIds
        internal: true
        json:
          - '.[].projectId'

  - engine:
      - sh
      - bash
    source: |
      gcloud container clusters list --project $projectId --format="json(name,location)"

    extractors:
      - type: json
        name: clusters
        internal: true
        json:
          - '.[]'

  - engine:
      - sh
      - bash
    source: |
      gcloud container clusters describe $clusterName --location $location --project $projectId --format="value(masterAuth.clientCertificateConfig.issueClientCertificate)"

    matchers:
      - type: word
        words:
          - "True"

    extractors:
      - type: dsl
        dsl:
          - '"GKE cluster " + clusterName + " in " + location + " of project " + projectId + " has client certificate authentication enabled"'
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