Unrestricted DNS Access in Azure NSGs

ID: azure-nsg-dns-unrestricted

Severity: high

Author: princechaddha

Tags: cloud,devops,azure,microsoft,nsg,azure-cloud-config

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.

YAML Source

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"'
# digest: 4a0a0047304502204889ed8818a8524f3159a1d3a3d76a735e91c7ad83e16baf1e7ff446d8170bff022100acc4945fdaf66e07b68ed825693f397becc30edabf5f5246d2f9ea13df264a75:922c64590222798bb761d5b6d8e72950

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/azure/network/azure-nsg-dns-unrestricted.yaml"

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