require_nsg_on_vnet.json

{
  "type": "Microsoft.Authorization/policyDefinitions",
  "name": "require_nsg_on_vnet",
  "properties": {
    "metadata": {
      "category": "Network"
    },
    "parameters": {
      "allowedRanges": {
        "type": "Array",
        "metadata": {
          "displayName": "Approved ranges",
          "description": "Provide the list of approved IP ranges for NSGs"
        }
      },
      "effect": {
        "type": "String",
        "defaultValue": "Audit",
        "allowedValues": [
          "Audit",
          "Deny",
          "Disabled"
        ],
        "metadata": {
          "displayName": "Effect",
          "description": "The effect determines what happens when the policy rule is evaluated to match"
        }
      }
    },
    "policyRule": {
      "if": {
        "anyOf": [
          {
            "allOf": [
              {
                "field": "type",
                "equals": "Microsoft.Network/networkSecurityGroups/securityRules"
              },
              {
                "anyOf": [
                  {
                    "field": "Microsoft.Network/networkSecurityGroups/securityRules/sourceAddressPrefix",
                    "notin": "[parameters('allowedRanges')]"
                  },
                  {
                    "field": "Microsoft.Network/networkSecurityGroups/securityRules/destinationAddressPrefix",
                    "notin": "[parameters('allowedRanges')]"
                  }
                ]
              }
            ]
          }
        ]
      },
      "then": {
        "effect": "[parameters('effect')]"
      }
    }
  }
}