azure-nsg-netbios-unrestricted: Unrestricted NetBIOS Access in Azure NSGs

id: azure-nsg-netbios-unrestricted
info:
  name: Unrestricted NetBIOS Access in Azure NSGs
  author: princechaddha
  severity: high
  description: |
    Ensure that Microsoft Azure network security groups (NSGs) do not allow unrestricted inbound access on TCP port 139 and UDP ports 137 and 138, used by NetBIOS, to protect against unauthorized network exploration and exploitation.
  impact: |
    Unrestricted NetBIOS access can expose network systems to information enumeration, system exploitation, and potential unauthorized access.
  remediation: |
    Update NSG rules to limit NetBIOS access to only necessary and secure sources, thereby enhancing the overall security posture of your network infrastructure.
  reference:
    - https://docs.microsoft.com/en-us/azure/virtual-network/network-security-groups-overview
  tags: cloud,devops,azure,microsoft,nsg,azure-cloud-config

flow: |
  code(1);
  for (let NsgData of iterate(template.nsgdata)) {
    NsgData = JSON.parse(NsgData)
    set("nsg", NsgData.name)
    set("resourcegroup", NsgData.resourceGroup)
    code(2)
  }

self-contained: true
code:
  - engine:
      - sh
      - bash
    source: |
      az network nsg list --query '[*].{name:name, resourceGroup:resourceGroup}' --output json

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

  - engine:
      - sh
      - bash
    source: |
      az network nsg rule list --nsg-name $nsg --resource-group $resourcegroup --query "[?direction=='Inbound' && access=='Allow' && (protocol=='TCP' && destinationPortRange=='139' || protocol=='UDP' && (destinationPortRange=='137' || destinationPortRange=='138'))]"

    matchers:
      - type: word
        words:
          - '"sourceAddressPrefix": "*"'
          - '"sourceAddressPrefix": "internet"'
          - '"sourceAddressPrefix": "any"'

    extractors:
      - type: dsl
        dsl:
          - 'nsg + " has unrestricted access on NetBIOS ports"'
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