Tailscale Device started advertising subnet routes

let recent =
    Tailscale_Devices_CL
    | where TimeGenerated > ago(1h)
    | summarize arg_max(TimeGenerated, *) by DeviceId
    | where array_length(AdvertisedRoutes) > 0;
let baseline =
    Tailscale_Devices_CL
    | where TimeGenerated between (ago(1d + 1h) .. ago(1h))
    | summarize arg_max(TimeGenerated, *) by DeviceId
    | where array_length(AdvertisedRoutes) > 0
    | distinct DeviceId;
recent
| join kind=leftanti baseline on DeviceId
| project TimeGenerated, DeviceId, DeviceName, Hostname, User, AdvertisedRoutes, EnabledRoutes, LastSeen

incidentConfiguration:
  createIncident: true
  groupingConfiguration:
    lookbackDuration: P1D
    reopenClosedIncident: false
    enabled: true
    matchingMethod: AllEntities
entityMappings:
- entityType: Host
  fieldMappings:
  - columnName: Hostname
    identifier: HostName
- entityType: Account
  fieldMappings:
  - columnName: User
    identifier: FullName
query: |
  let recent =
      Tailscale_Devices_CL
      | where TimeGenerated > ago(1h)
      | summarize arg_max(TimeGenerated, *) by DeviceId
      | where array_length(AdvertisedRoutes) > 0;
  let baseline =
      Tailscale_Devices_CL
      | where TimeGenerated between (ago(1d + 1h) .. ago(1h))
      | summarize arg_max(TimeGenerated, *) by DeviceId
      | where array_length(AdvertisedRoutes) > 0
      | distinct DeviceId;
  recent
  | join kind=leftanti baseline on DeviceId
  | project TimeGenerated, DeviceId, DeviceName, Hostname, User, AdvertisedRoutes, EnabledRoutes, LastSeen
id: c2b3d4e5-2345-6789-01ab-cdef12345002
queryFrequency: 1h
status: Available
version: 1.0.0
severity: Medium
relevantTechniques:
- T1021
- T1556
name: 'Tailscale: Device started advertising subnet routes'
kind: Scheduled
tactics:
- LateralMovement
- Persistence
requiredDataConnectors:
- dataTypes:
  - Tailscale_Devices_CL
  connectorId: TailscaleCCF
description: |
  Identifies when a tailnet device begins advertising subnet routes (subnet-router capability) not present in the previous snapshot. Unexpected advertisement may indicate a compromised node expanding reachable surface area or an unsanctioned admin change.
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Tailscale%20%28CCF%29/Analytic%20Rules/TailscaleDeviceAdvertisingSubnetRoutes.yaml
triggerOperator: gt
triggerThreshold: 0
queryPeriod: 1d

{
  "$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/c2b3d4e5-2345-6789-01ab-cdef12345002')]",
      "kind": "Scheduled",
      "name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/c2b3d4e5-2345-6789-01ab-cdef12345002')]",
      "properties": {
        "alertRuleTemplateName": "c2b3d4e5-2345-6789-01ab-cdef12345002",
        "customDetails": null,
        "description": "Identifies when a tailnet device begins advertising subnet routes (subnet-router capability) not present in the previous snapshot. Unexpected advertisement may indicate a compromised node expanding reachable surface area or an unsanctioned admin change.\n",
        "displayName": "Tailscale: Device started advertising subnet routes",
        "enabled": true,
        "entityMappings": [
          {
            "entityType": "Host",
            "fieldMappings": [
              {
                "columnName": "Hostname",
                "identifier": "HostName"
              }
            ]
          },
          {
            "entityType": "Account",
            "fieldMappings": [
              {
                "columnName": "User",
                "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/TailscaleDeviceAdvertisingSubnetRoutes.yaml",
        "query": "let recent =\n    Tailscale_Devices_CL\n    | where TimeGenerated > ago(1h)\n    | summarize arg_max(TimeGenerated, *) by DeviceId\n    | where array_length(AdvertisedRoutes) > 0;\nlet baseline =\n    Tailscale_Devices_CL\n    | where TimeGenerated between (ago(1d + 1h) .. ago(1h))\n    | summarize arg_max(TimeGenerated, *) by DeviceId\n    | where array_length(AdvertisedRoutes) > 0\n    | distinct DeviceId;\nrecent\n| join kind=leftanti baseline on DeviceId\n| project TimeGenerated, DeviceId, DeviceName, Hostname, User, AdvertisedRoutes, EnabledRoutes, LastSeen\n",
        "queryFrequency": "PT1H",
        "queryPeriod": "P1D",
        "severity": "Medium",
        "status": "Available",
        "subTechniques": [],
        "suppressionDuration": "PT1H",
        "suppressionEnabled": false,
        "tactics": [
          "LateralMovement",
          "Persistence"
        ],
        "techniques": [
          "T1021",
          "T1556"
        ],
        "templateVersion": "1.0.0",
        "triggerOperator": "GreaterThan",
        "triggerThreshold": 0
      },
      "type": "Microsoft.OperationalInsights/workspaces/providers/alertRules"
    }
  ]
}