IP Forwarding Not Disabled for VM Instances

ID: gcloud-vm-ip-forwarding-enabled

Severity: medium

Author: princechaddha

Tags: cloud,devops,gcp,gcloud,compute,security,networking,ip-forwarding,gcp-cloud-config

Description

Ensure that IP Forwarding feature is not enabled at the Google Compute Engine instance level for security and compliance reasons, as instances with IP Forwarding enabled act as routers/packet forwarders. Because IP forwarding is rarely required, except when the virtual machine (VM) is used as a network virtual appliance, each Google Cloud VM instance should be reviewed to decide whether IP forwarding is really needed.

YAML Source

id: gcloud-vm-ip-forwarding-enabled

info:
  name: IP Forwarding Not Disabled for VM Instances
  author: princechaddha
  severity: medium
  description: |
    Ensure that IP Forwarding feature is not enabled at the Google Compute Engine instance level for security and compliance reasons, as instances with IP Forwarding enabled act as routers/packet forwarders. Because IP forwarding is rarely required, except when the virtual machine (VM) is used as a network virtual appliance, each Google Cloud VM instance should be reviewed to decide whether IP forwarding is really needed.
  impact: |
    With IP forwarding enabled, VM instances can act as routers and receive traffic addressed to other destinations, potentially creating security risks if not properly configured and monitored.
  remediation: |
    Re-create your VM instances with IP forwarding disabled. Note that you cannot disable IP forwarding on an existing instance - you must create a new instance without the IP forwarding option.
  reference:
    - https://www.trendmicro.com/cloudoneconformity/knowledge-base/gcp/ComputeEngine/disable-ip-forwarding.html
    - https://cloud.google.com/vpc/docs/using-routes
  tags: cloud,devops,gcp,gcloud,compute,security,networking,ip-forwarding,gcp-cloud-config

flow: |
  code(1)
  for(let projectId of iterate(template.projectIds)){
    set("projectId", projectId)
    code(2)
    for(let instance of iterate(template.instances)){
      instance = JSON.parse(instance)
      set("instanceName", instance.name)
      set("zone", instance.zone)
      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 compute instances list --project $projectId --format="json(name,zone.basename())"

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

  - engine:
      - sh
      - bash
    source: |
      gcloud compute instances describe $instanceName --zone $zone --project $projectId --format="json(canIpForward)"

    matchers:
      - type: word
        words:
          - '"canIpForward": true'

    extractors:
      - type: dsl
        dsl:
          - '"VM instance " + instanceName + " in zone " + zone + " of project " + projectId + " has IP forwarding enabled"'
# digest: 4a0a00473045022018552b2c39c97674f9ea1def9c2e218bd5a11e55f6b92a483d9dfc474375f2890221008434dd3e48c93627232b1acdefbd19b76d8f6e853fd79250e487b0d5064ea362:922c64590222798bb761d5b6d8e72950

Guide to check the vulnerabilities

This template is used to detect vulnerabilities in web applications. It can be used with the Nuclei tool to scan for specific patterns or behaviors.

$ nuclei -u "URL" -t "cloud/gcp/compute/gcloud-vm-ip-forwarding-enabled.yaml"

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