Potential DGA detected ASIM DNS Schema

let referencestarttime = 10d;
let referenceendtime = 1d;
let threshold = 100;
let nxDomainDnsEvents = (stime:datetime, etime:datetime) 
  {_Im_Dns(responsecodename='NXDOMAIN', starttime=stime, endtime=etime)
  | where DnsQueryTypeName in ("A", "AAAA")
  | where ipv4_is_match("127.0.0.1", SrcIpAddr) == False
  | where DnsQuery !contains "/" and  DnsQuery contains "."};
nxDomainDnsEvents (stime=ago(referenceendtime) ,etime=now())
  | extend sld = tostring(split(DnsQuery, ".")[-2])
  | summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated), dcount(sld) by SrcIpAddr
  | where dcount_sld > threshold
  // Filter out previously seen IPs
  | join kind=leftanti (nxDomainDnsEvents (stime=ago(referencestarttime), etime=ago(referenceendtime))
    | extend sld = tostring(split(DnsQuery, ".")[-2])
    | summarize dcount(sld) by SrcIpAddr
    | where dcount_sld > threshold ) on SrcIpAddr
// Pull out sample NXDomain responses for those remaining potentially infected IPs
| join kind = inner (nxDomainDnsEvents (stime=ago(referencestarttime), etime=now()) | summarize by DnsQuery, SrcIpAddr) on SrcIpAddr
| summarize StartTime = min(StartTime), EndTime = max(EndTime), sampleNXDomainList=make_list(DnsQuery, 100)  by SrcIpAddr, dcount_sld

tactics:
- CommandAndControl
relevantTechniques:
- T1568
- T1008
id: 983a6922-894d-413c-9f04-d7add0ecc307
severity: Medium
name: Potential DGA detected (ASIM DNS Schema)
requiredDataConnectors:
- connectorId: DNS
  dataTypes:
  - DnsEvents
- connectorId: AzureFirewall
  dataTypes:
  - AzureDiagnostics
- connectorId: Zscaler
  dataTypes:
  - CommonSecurityLog
- connectorId: InfobloxNIOS
  dataTypes:
  - Syslog
- connectorId: GCPDNSDataConnector
  dataTypes:
  - GCP_DNS_CL
- connectorId: NXLogDnsLogs
  dataTypes:
  - NXLog_DNS_Server_CL
- connectorId: CiscoUmbrellaDataConnector
  dataTypes:
  - Cisco_Umbrella_dns_CL
- connectorId: Corelight
  dataTypes:
  - Corelight_CL
query: |
  let referencestarttime = 10d;
  let referenceendtime = 1d;
  let threshold = 100;
  let nxDomainDnsEvents = (stime:datetime, etime:datetime) 
    {_Im_Dns(responsecodename='NXDOMAIN', starttime=stime, endtime=etime)
    | where DnsQueryTypeName in ("A", "AAAA")
    | where ipv4_is_match("127.0.0.1", SrcIpAddr) == False
    | where DnsQuery !contains "/" and  DnsQuery contains "."};
  nxDomainDnsEvents (stime=ago(referenceendtime) ,etime=now())
    | extend sld = tostring(split(DnsQuery, ".")[-2])
    | summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated), dcount(sld) by SrcIpAddr
    | where dcount_sld > threshold
    // Filter out previously seen IPs
    | join kind=leftanti (nxDomainDnsEvents (stime=ago(referencestarttime), etime=ago(referenceendtime))
      | extend sld = tostring(split(DnsQuery, ".")[-2])
      | summarize dcount(sld) by SrcIpAddr
      | where dcount_sld > threshold ) on SrcIpAddr
  // Pull out sample NXDomain responses for those remaining potentially infected IPs
  | join kind = inner (nxDomainDnsEvents (stime=ago(referencestarttime), etime=now()) | summarize by DnsQuery, SrcIpAddr) on SrcIpAddr
  | summarize StartTime = min(StartTime), EndTime = max(EndTime), sampleNXDomainList=make_list(DnsQuery, 100)  by SrcIpAddr, dcount_sld  
queryPeriod: 10d
entityMappings:
- entityType: IP
  fieldMappings:
  - identifier: Address
    columnName: SrcIpAddr
tags:
- version: 1.0.0
  ParentAlert: https://github.com/Azure/Azure-Sentinel/blob/master/Detections/DnsEvents/DNS_HighNXDomainCount_detection.yaml
- Schema: ASIMDns
  SchemaVersion: 0.1.1
triggerOperator: gt
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Detections/ASimDNS/imDns_HighNXDomainCount_detection.yaml
triggerThreshold: 0
description: |
  'Identifies clients with a high NXDomain count which could be indicative of a DGA (cycling through possible C2 domains where most C2s are not live). Alert is generated when a new IP address is seen (based on not being seen associated with 
  NXDomain records in prior 10-day baseline period).
  This analytic rule uses [ASIM](https://aka.ms/AboutASIM) and supports any built-in or custom source that supports the ASIM DNS schema'  
version: 1.3.4
metadata:
  categories:
    domains:
    - Security - Network
  author:
    name: Yaron
  source:
    kind: Community
  support:
    tier: Community
queryFrequency: 1d
kind: Scheduled

{
  "$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/983a6922-894d-413c-9f04-d7add0ecc307')]",
      "kind": "Scheduled",
      "name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/983a6922-894d-413c-9f04-d7add0ecc307')]",
      "properties": {
        "alertRuleTemplateName": "983a6922-894d-413c-9f04-d7add0ecc307",
        "customDetails": null,
        "description": "'Identifies clients with a high NXDomain count which could be indicative of a DGA (cycling through possible C2 domains where most C2s are not live). Alert is generated when a new IP address is seen (based on not being seen associated with \nNXDomain records in prior 10-day baseline period).\nThis analytic rule uses [ASIM](https://aka.ms/AboutASIM) and supports any built-in or custom source that supports the ASIM DNS schema'\n",
        "displayName": "Potential DGA detected (ASIM DNS Schema)",
        "enabled": true,
        "entityMappings": [
          {
            "entityType": "IP",
            "fieldMappings": [
              {
                "columnName": "SrcIpAddr",
                "identifier": "Address"
              }
            ]
          }
        ],
        "OriginalUri": "https://github.com/Azure/Azure-Sentinel/blob/master/Detections/ASimDNS/imDns_HighNXDomainCount_detection.yaml",
        "query": "let referencestarttime = 10d;\nlet referenceendtime = 1d;\nlet threshold = 100;\nlet nxDomainDnsEvents = (stime:datetime, etime:datetime) \n  {_Im_Dns(responsecodename='NXDOMAIN', starttime=stime, endtime=etime)\n  | where DnsQueryTypeName in (\"A\", \"AAAA\")\n  | where ipv4_is_match(\"127.0.0.1\", SrcIpAddr) == False\n  | where DnsQuery !contains \"/\" and  DnsQuery contains \".\"};\nnxDomainDnsEvents (stime=ago(referenceendtime) ,etime=now())\n  | extend sld = tostring(split(DnsQuery, \".\")[-2])\n  | summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated), dcount(sld) by SrcIpAddr\n  | where dcount_sld > threshold\n  // Filter out previously seen IPs\n  | join kind=leftanti (nxDomainDnsEvents (stime=ago(referencestarttime), etime=ago(referenceendtime))\n    | extend sld = tostring(split(DnsQuery, \".\")[-2])\n    | summarize dcount(sld) by SrcIpAddr\n    | where dcount_sld > threshold ) on SrcIpAddr\n// Pull out sample NXDomain responses for those remaining potentially infected IPs\n| join kind = inner (nxDomainDnsEvents (stime=ago(referencestarttime), etime=now()) | summarize by DnsQuery, SrcIpAddr) on SrcIpAddr\n| summarize StartTime = min(StartTime), EndTime = max(EndTime), sampleNXDomainList=make_list(DnsQuery, 100)  by SrcIpAddr, dcount_sld\n",
        "queryFrequency": "P1D",
        "queryPeriod": "P10D",
        "severity": "Medium",
        "subTechniques": [],
        "suppressionDuration": "PT1H",
        "suppressionEnabled": false,
        "tactics": [
          "CommandAndControl"
        ],
        "tags": [
          {
            "ParentAlert": "https://github.com/Azure/Azure-Sentinel/blob/master/Detections/DnsEvents/DNS_HighNXDomainCount_detection.yaml",
            "version": "1.0.0"
          },
          {
            "Schema": "ASIMDns",
            "SchemaVersion": "0.1.1"
          }
        ],
        "techniques": [
          "T1008",
          "T1568"
        ],
        "templateVersion": "1.3.4",
        "triggerOperator": "GreaterThan",
        "triggerThreshold": 0
      },
      "type": "Microsoft.OperationalInsights/workspaces/providers/alertRules"
    }
  ]
}