azure-nsg-dns-unrestricted: Unrestricted DNS Access in Azure NSGs

id: azure-nsg-dns-unrestricted
info:
  name: Unrestricted DNS 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 and UDP port 53 to prevent DNS amplification attacks and other DNS-related threats.
  impact: |
    Allowing unrestricted access on TCP and UDP port 53 can make DNS servers vulnerable to various types of cyber attacks, disrupting network operations.
  remediation: |
    Restrict access to DNS services by configuring NSG rules to only allow trusted sources and necessary traffic on TCP and UDP port 53.
  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' || protocol=='UDP') && (destinationPortRange=='53')]"

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

    extractors:
      - type: dsl
        dsl:
          - 'nsg + " has unrestricted access on TCP and UDP port 53"'
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