id: gcloud-org-ip-forwarding

info:
  name: VM IP Forwarding Not Restricted
  author: princechaddha
  severity: medium
  description: |
    Ensure that the virtual machine (VM) instances allowed to use IP forwarding, that belong to your project, folder, or organization, are defined using the "Restrict VM IP Forwarding" policy. This constraint policy helps you improve security and achieve regulatory compliance by explicitly defining the resource name of the VM instances allowed to use IP forwarding.
  impact: |
    By default, any virtual machine instance can enable IP forwarding in any VPC network. When IP forwarding is enabled on a VM's network interface, it allows the VM to act as a router and receive traffic addressed to other destinations, which could be exploited for malicious purposes.
  remediation: |
    Configure the "Restrict VM IP Forwarding" policy at the organization level to explicitly specify which VM instances can use IP forwarding. Use the format projects/<project-id>/zones/<instance-zone>/instances/<instance-name> or under: prefix for broader scopes.
  reference:
    - https://www.trendmicro.com/cloudoneconformity/knowledge-base/gcp/ResourceManager/enable-ip-forwarding-restriction-policy.html
    - https://cloud.google.com/vpc/docs/using-instance-ip-forwarding
  tags: cloud,devops,gcp,gcloud,resourcemanager,security,networking,ip-forwarding,gcp-cloud-config

flow: |
  code(1)
  for(let orgId of iterate(template.orgIds)){
    set("orgId", orgId)
    code(2)
  }

self-contained: true

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

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

  - engine:
      - sh
      - bash
    source: |
      gcloud alpha resource-manager org-policies describe compute.vmCanIpForward --organization=$orgId --effective --format="json(listPolicy.allValues)"

    matchers:
      - type: word
        words:
          - "ALLOW"

    extractors:
      - type: dsl
        dsl:
          - '"Organization " + orgId + " has not restricted VM IP forwarding, allowing any instance to act as a router"'
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