Tailscale Premium DERP relay traffic surge

let minFlows = 20;
let relayedPctThreshold = 75.0;
Tailscale_Network_CL
| where TimeGenerated > ago(15m)
| summarize
    TotalFlows = count(),
    RelayedFlows = countif(IsRelayed)
    by SrcNodeName, SrcUser, SrcOs, SrcTags=tostring(SrcTags)
| where TotalFlows >= minFlows
| extend RelayedPct = round(100.0 * RelayedFlows / TotalFlows, 1)
| where RelayedPct > relayedPctThreshold
| project SrcNodeName, SrcUser, SrcOs, SrcTags, TotalFlows, RelayedFlows, RelayedPct
| order by RelayedPct desc

incidentConfiguration:
  groupingConfiguration:
    lookbackDuration: PT6H
    reopenClosedIncident: false
    matchingMethod: AllEntities
    enabled: true
  createIncident: true
name: 'Tailscale Premium: DERP relay traffic surge'
triggerOperator: gt
query: |
  let minFlows = 20;
  let relayedPctThreshold = 75.0;
  Tailscale_Network_CL
  | where TimeGenerated > ago(15m)
  | summarize
      TotalFlows = count(),
      RelayedFlows = countif(IsRelayed)
      by SrcNodeName, SrcUser, SrcOs, SrcTags=tostring(SrcTags)
  | where TotalFlows >= minFlows
  | extend RelayedPct = round(100.0 * RelayedFlows / TotalFlows, 1)
  | where RelayedPct > relayedPctThreshold
  | project SrcNodeName, SrcUser, SrcOs, SrcTags, TotalFlows, RelayedFlows, RelayedPct
  | order by RelayedPct desc
queryFrequency: 15m
description: Identifies when a source node has more than 75 percent of its recent flows falling back to a DERP relay (Tailscale IsRelayed flag, traffic via 127.3.3.40). Operational signal useful for spotting policy drift.
id: 0a1c8d12-e7d3-4890-8b89-8d6dbc1be2f0
triggerThreshold: 0
queryPeriod: 15m
version: 1.0.0
kind: Scheduled
status: Available
severity: Low
requiredDataConnectors:
- connectorId: TailscalePremiumCCF
  dataTypes:
  - Tailscale_Network_CL
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Tailscale%20%28CCF%29/Analytic%20Rules/TailscalePremiumDerpRelaySurge.yaml
description-detailed: |
  Identifies when a source node has more than 75 percent of its recent flows falling back to a DERP relay (Tailscale's IsRelayed flag, traffic via 127.3.3.40). Sustained high relay rate indicates direct WireGuard peer-to-peer is failing - causes include NAT/firewall changes, a network blocking UDP 41641, or potential evasion attempts. Operational signal but useful for spotting policy drift. Requires Tailscale Premium or Enterprise.
relevantTechniques:
- T1572
tactics:
- CommandAndControl
entityMappings:
- fieldMappings:
  - identifier: HostName
    columnName: SrcNodeName
  entityType: Host
- fieldMappings:
  - identifier: FullName
    columnName: SrcUser
  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/0a1c8d12-e7d3-4890-8b89-8d6dbc1be2f0')]",
      "kind": "Scheduled",
      "name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/0a1c8d12-e7d3-4890-8b89-8d6dbc1be2f0')]",
      "properties": {
        "alertRuleTemplateName": "0a1c8d12-e7d3-4890-8b89-8d6dbc1be2f0",
        "customDetails": null,
        "description": "Identifies when a source node has more than 75 percent of its recent flows falling back to a DERP relay (Tailscale IsRelayed flag, traffic via 127.3.3.40). Operational signal useful for spotting policy drift.",
        "description-detailed": "Identifies when a source node has more than 75 percent of its recent flows falling back to a DERP relay (Tailscale's IsRelayed flag, traffic via 127.3.3.40). Sustained high relay rate indicates direct WireGuard peer-to-peer is failing - causes include NAT/firewall changes, a network blocking UDP 41641, or potential evasion attempts. Operational signal but useful for spotting policy drift. Requires Tailscale Premium or Enterprise.\n",
        "displayName": "Tailscale Premium: DERP relay traffic surge",
        "enabled": true,
        "entityMappings": [
          {
            "entityType": "Host",
            "fieldMappings": [
              {
                "columnName": "SrcNodeName",
                "identifier": "HostName"
              }
            ]
          },
          {
            "entityType": "Account",
            "fieldMappings": [
              {
                "columnName": "SrcUser",
                "identifier": "FullName"
              }
            ]
          }
        ],
        "incidentConfiguration": {
          "createIncident": true,
          "groupingConfiguration": {
            "enabled": true,
            "lookbackDuration": "PT6H",
            "matchingMethod": "AllEntities",
            "reopenClosedIncident": false
          }
        },
        "OriginalUri": "https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Tailscale%20%28CCF%29/Analytic%20Rules/TailscalePremiumDerpRelaySurge.yaml",
        "query": "let minFlows = 20;\nlet relayedPctThreshold = 75.0;\nTailscale_Network_CL\n| where TimeGenerated > ago(15m)\n| summarize\n    TotalFlows = count(),\n    RelayedFlows = countif(IsRelayed)\n    by SrcNodeName, SrcUser, SrcOs, SrcTags=tostring(SrcTags)\n| where TotalFlows >= minFlows\n| extend RelayedPct = round(100.0 * RelayedFlows / TotalFlows, 1)\n| where RelayedPct > relayedPctThreshold\n| project SrcNodeName, SrcUser, SrcOs, SrcTags, TotalFlows, RelayedFlows, RelayedPct\n| order by RelayedPct desc\n",
        "queryFrequency": "PT15M",
        "queryPeriod": "PT15M",
        "severity": "Low",
        "status": "Available",
        "subTechniques": [],
        "suppressionDuration": "PT1H",
        "suppressionEnabled": false,
        "tactics": [
          "CommandAndControl"
        ],
        "techniques": [
          "T1572"
        ],
        "templateVersion": "1.0.0",
        "triggerOperator": "GreaterThan",
        "triggerThreshold": 0
      },
      "type": "Microsoft.OperationalInsights/workspaces/providers/alertRules"
    }
  ]
}