gcloud-pubsub-crossproject-access: Pub/Sub Subscription Cross-Project Access

id: gcloud-pubsub-crossproject-access

info:
  name: Pub/Sub Subscription Cross-Project Access
  author: princechaddha
  severity: high
  description: |
    Ensure that your Google Cloud Pub/Sub subscriptions are configured to allow access only to trusted GCP projects to protect against unauthorized cross-project access. The list with the trusted GCP projects must be defined in the conformity rule settings, in the Trend Cloud One™ – Conformity account console.
  impact: |
    Allowing access to Pub/Sub subscriptions from untrusted GCP projects can lead to unauthorized data access, privilege escalation, and potential data exfiltration.
  remediation: |
    Restrict access to Pub/Sub subscriptions by configuring IAM policies to include only trusted service accounts or users. Ensure roles such as "roles/pubsub.subscriber", "roles/pubsub.editor", or "roles/pubsub.admin" are only assigned to trusted principals.
  reference:
    - https://cloud.google.com/pubsub/docs/access-control
    - https://cloudone.trendmicro.com/docs/conformity
  tags: cloud,devops,gcp,gcloud,google-cloud-pubsub,gcp-cloud-config

flow: |
  code(1)
  for(let projectId of iterate(template.projectIds)){
    set("projectId", projectId)
    code(2)
    for(let pubsubSubscription of iterate(template.subscriptions)){
      set("subscriptionName", pubsubSubscription)
      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 pubsub subscriptions list --project $projectId --format="json(name)"

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

  - engine:
      - sh
      - bash
    source: |
      gcloud pubsub subscriptions get-iam-policy $subscriptionName --format=json | jq '.bindings[]'

    matchers:
      - type: word
        words:
          - '@'

    extractors:
      - type: dsl
        dsl:
          - '"Pub/Sub subscription " + subscriptionName + " in project " + projectId + " has cross-project access configured with one or more untrusted members."'
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