Tailscale Split-DNS configuration modified

Tailscale_Audit_CL
| where Action == "UPDATE"
| where tostring(Target.type) == "TAILNET"
| where tostring(Target.property) == "DNS_SPLIT_DNS"
| extend ActorLogin = tostring(Actor.loginName)
| extend OldDomains = bag_keys(Old)
| extend NewDomains = bag_keys(New)
| extend AddedDomains = set_difference(NewDomains, OldDomains)
| extend RemovedDomains = set_difference(OldDomains, NewDomains)
| project TimeGenerated, ActorLogin, AddedDomains, RemovedDomains, Old, New, Origin

incidentConfiguration:
  groupingConfiguration:
    lookbackDuration: P1D
    reopenClosedIncident: false
    matchingMethod: AllEntities
    enabled: true
  createIncident: true
name: 'Tailscale: Split-DNS configuration modified'
triggerOperator: gt
query: |
  Tailscale_Audit_CL
  | where Action == "UPDATE"
  | where tostring(Target.type) == "TAILNET"
  | where tostring(Target.property) == "DNS_SPLIT_DNS"
  | extend ActorLogin = tostring(Actor.loginName)
  | extend OldDomains = bag_keys(Old)
  | extend NewDomains = bag_keys(New)
  | extend AddedDomains = set_difference(NewDomains, OldDomains)
  | extend RemovedDomains = set_difference(OldDomains, NewDomains)
  | project TimeGenerated, ActorLogin, AddedDomains, RemovedDomains, Old, New, Origin
queryFrequency: 15m
description: |
  Identifies when the tailnet split-DNS configuration is modified. Split-DNS overrides per-domain resolution within the tailnet - an attacker adding a new domain mapping or changing the resolver IP can hijack DNS for that domain.
id: b4c5d6e7-1234-5678-90ab-cdef12345010
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/TailscaleSplitDnsModified.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/b4c5d6e7-1234-5678-90ab-cdef12345010')]",
      "kind": "Scheduled",
      "name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/b4c5d6e7-1234-5678-90ab-cdef12345010')]",
      "properties": {
        "alertRuleTemplateName": "b4c5d6e7-1234-5678-90ab-cdef12345010",
        "customDetails": null,
        "description": "Identifies when the tailnet split-DNS configuration is modified. Split-DNS overrides per-domain resolution within the tailnet - an attacker adding a new domain mapping or changing the resolver IP can hijack DNS for that domain.\n",
        "displayName": "Tailscale: Split-DNS configuration 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/TailscaleSplitDnsModified.yaml",
        "query": "Tailscale_Audit_CL\n| where Action == \"UPDATE\"\n| where tostring(Target.type) == \"TAILNET\"\n| where tostring(Target.property) == \"DNS_SPLIT_DNS\"\n| extend ActorLogin = tostring(Actor.loginName)\n| extend OldDomains = bag_keys(Old)\n| extend NewDomains = bag_keys(New)\n| extend AddedDomains = set_difference(NewDomains, OldDomains)\n| extend RemovedDomains = set_difference(OldDomains, NewDomains)\n| project TimeGenerated, ActorLogin, AddedDomains, RemovedDomains, Old, New, 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"
    }
  ]
}