Tailscale DNS nameservers modified

Tailscale_Audit_CL
| where Action == "UPDATE"
| where tostring(Target.type) == "TAILNET"
| where tostring(Target.property) == "DNS_NAMESERVERS"
| extend ActorLogin = tostring(Actor.loginName)
| extend OldServers = Old.dns
| extend NewServers = New.dns
| extend Added = set_difference(NewServers, OldServers)
| extend Removed = set_difference(OldServers, NewServers)
| project TimeGenerated, ActorLogin, OldServers, NewServers, Added, Removed, Origin

incidentConfiguration:
  groupingConfiguration:
    lookbackDuration: P1D
    reopenClosedIncident: false
    matchingMethod: AllEntities
    enabled: true
  createIncident: true
name: 'Tailscale: DNS nameservers modified'
triggerOperator: gt
query: |
  Tailscale_Audit_CL
  | where Action == "UPDATE"
  | where tostring(Target.type) == "TAILNET"
  | where tostring(Target.property) == "DNS_NAMESERVERS"
  | extend ActorLogin = tostring(Actor.loginName)
  | extend OldServers = Old.dns
  | extend NewServers = New.dns
  | extend Added = set_difference(NewServers, OldServers)
  | extend Removed = set_difference(OldServers, NewServers)
  | project TimeGenerated, ActorLogin, OldServers, NewServers, Added, Removed, Origin
queryFrequency: 15m
description: |
  Identifies when the tailnet's global DNS nameserver list is modified. Adding an attacker-controlled resolver as a tailnet-wide nameserver enables broad DNS hijacking for every device using MagicDNS resolution.
id: c5d6e7f8-2345-6789-01ab-cdef12345011
triggerThreshold: 0
queryPeriod: 15m
version: 1.0.0
kind: Scheduled
status: Available
severity: High
requiredDataConnectors:
- connectorId: TailscaleCCF
  dataTypes:
  - Tailscale_Audit_CL
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Tailscale%20%28CCF%29/Analytic%20Rules/TailscaleDnsNameserversModified.yaml
relevantTechniques:
- T1556
- T1568
tactics:
- DefenseEvasion
- CommandAndControl
entityMappings:
- fieldMappings:
  - identifier: FullName
    columnName: ActorLogin
  entityType: Account

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "parameters": {
    "workspace": {
      "type": "String"
    }
  },
  "resources": [
    {
      "apiVersion": "2024-01-01-preview",
      "id": "[concat(resourceId('Microsoft.OperationalInsights/workspaces/providers', parameters('workspace'), 'Microsoft.SecurityInsights'),'/alertRules/c5d6e7f8-2345-6789-01ab-cdef12345011')]",
      "kind": "Scheduled",
      "name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/c5d6e7f8-2345-6789-01ab-cdef12345011')]",
      "properties": {
        "alertRuleTemplateName": "c5d6e7f8-2345-6789-01ab-cdef12345011",
        "customDetails": null,
        "description": "Identifies when the tailnet's global DNS nameserver list is modified. Adding an attacker-controlled resolver as a tailnet-wide nameserver enables broad DNS hijacking for every device using MagicDNS resolution.\n",
        "displayName": "Tailscale: DNS nameservers modified",
        "enabled": true,
        "entityMappings": [
          {
            "entityType": "Account",
            "fieldMappings": [
              {
                "columnName": "ActorLogin",
                "identifier": "FullName"
              }
            ]
          }
        ],
        "incidentConfiguration": {
          "createIncident": true,
          "groupingConfiguration": {
            "enabled": true,
            "lookbackDuration": "P1D",
            "matchingMethod": "AllEntities",
            "reopenClosedIncident": false
          }
        },
        "OriginalUri": "https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Tailscale%20%28CCF%29/Analytic%20Rules/TailscaleDnsNameserversModified.yaml",
        "query": "Tailscale_Audit_CL\n| where Action == \"UPDATE\"\n| where tostring(Target.type) == \"TAILNET\"\n| where tostring(Target.property) == \"DNS_NAMESERVERS\"\n| extend ActorLogin = tostring(Actor.loginName)\n| extend OldServers = Old.dns\n| extend NewServers = New.dns\n| extend Added = set_difference(NewServers, OldServers)\n| extend Removed = set_difference(OldServers, NewServers)\n| project TimeGenerated, ActorLogin, OldServers, NewServers, Added, Removed, Origin\n",
        "queryFrequency": "PT15M",
        "queryPeriod": "PT15M",
        "severity": "High",
        "status": "Available",
        "subTechniques": [],
        "suppressionDuration": "PT1H",
        "suppressionEnabled": false,
        "tactics": [
          "CommandAndControl",
          "DefenseEvasion"
        ],
        "techniques": [
          "T1556",
          "T1568"
        ],
        "templateVersion": "1.0.0",
        "triggerOperator": "GreaterThan",
        "triggerThreshold": 0
      },
      "type": "Microsoft.OperationalInsights/workspaces/providers/alertRules"
    }
  ]
}