Rare client observed with high reverse DNS lookup count - Static threshold based (ASIM DNS Solution)

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Id	77b7c820-5f60-4779-8bdb-f06e21add5f1
Rulename	Rare client observed with high reverse DNS lookup count - Static threshold based (ASIM DNS Solution)
Description	This rule identifies clients with high reverse DNS counts, which could be carrying out reconnaissance or discovery activity. This helps in detecting the possible initial phases of an attack, like discovery and reconnaissance. \n\nIt utilizes ASIM normalization and is applied to any source that supports the ASIM DNS schema.
Severity	Medium
Tactics	Reconnaissance
Techniques	T1590
Required data connectors	AIVectraStream ASimDnsActivityLogs AzureFirewall CiscoUmbrellaDataConnector Corelight DNS GCPDNSDataConnector InfobloxNIOS ISCBind NXLogDnsLogs WindowsForwardedEvents Zscaler
Kind	Scheduled
Query frequency	1d
Query period	10d
Trigger threshold	0
Trigger operator	gt
Source Uri	https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/DNS Essentials/Analytic Rules/RareClientObservedWithHighReverseDNSLookupCountStaticThresholdBased.yaml
Version	1.0.0
Arm template	77b7c820-5f60-4779-8bdb-f06e21add5f1.json

KQL

let threshold = materialize (_GetWatchlist('DNS_Solution_Monitoring_Configuration')
  | where wl_RuleName == 'Rare client observed with high reverse DNS lookup'
      and wl_Type == 'Detection'
  | project toint(wl_Threshold));
let stime = 10d;
let etime = 1d;
let SearchDomain = dynamic(["in-addr.arpa"]);
_Im_Dns(starttime=ago(etime), domain_has_any=SearchDomain)
| summarize
  StartTimeUtc = min(TimeGenerated),
  EndTimeUtc = max(TimeGenerated),
  DNSQueryCount=dcount(DnsQuery)
  by SrcIpAddr
| where DNSQueryCount > toscalar(threshold)
| project StartTimeUtc, EndTimeUtc, SrcIpAddr, DNSQueryCount 
| join kind=leftanti (_Im_Dns(starttime=ago(stime), endtime=ago(etime), domain_has_any=SearchDomain)
  | summarize DNSQueryCount=dcount(DnsQuery) by SrcIpAddr, bin(TimeGenerated, 1d)
  | where DNSQueryCount > toscalar(threshold)
  | project SrcIpAddr, DNSQueryCount
  )
  on SrcIpAddr
| join kind=inner (_Im_Dns(starttime=ago(etime), domain_has_any=SearchDomain)
  | summarize DNSQueries=make_set(DnsQuery, 1000) by SrcIpAddr)
  on SrcIpAddr
| extend DNSQuerythreshold = toint(toscalar(threshold))
| project-away SrcIpAddr1

YAML

query: |
  let threshold = materialize (_GetWatchlist('DNS_Solution_Monitoring_Configuration')
    | where wl_RuleName == 'Rare client observed with high reverse DNS lookup'
        and wl_Type == 'Detection'
    | project toint(wl_Threshold));
  let stime = 10d;
  let etime = 1d;
  let SearchDomain = dynamic(["in-addr.arpa"]);
  _Im_Dns(starttime=ago(etime), domain_has_any=SearchDomain)
  | summarize
    StartTimeUtc = min(TimeGenerated),
    EndTimeUtc = max(TimeGenerated),
    DNSQueryCount=dcount(DnsQuery)
    by SrcIpAddr
  | where DNSQueryCount > toscalar(threshold)
  | project StartTimeUtc, EndTimeUtc, SrcIpAddr, DNSQueryCount 
  | join kind=leftanti (_Im_Dns(starttime=ago(stime), endtime=ago(etime), domain_has_any=SearchDomain)
    | summarize DNSQueryCount=dcount(DnsQuery) by SrcIpAddr, bin(TimeGenerated, 1d)
    | where DNSQueryCount > toscalar(threshold)
    | project SrcIpAddr, DNSQueryCount
    )
    on SrcIpAddr
  | join kind=inner (_Im_Dns(starttime=ago(etime), domain_has_any=SearchDomain)
    | summarize DNSQueries=make_set(DnsQuery, 1000) by SrcIpAddr)
    on SrcIpAddr
  | extend DNSQuerythreshold = toint(toscalar(threshold))
  | project-away SrcIpAddr1  
eventGroupingSettings:
  aggregationKind: AlertPerResult
triggerThreshold: 0
customDetails:
  DNSQuerythreshold: DNSQuerythreshold
  DNSQueries: DNSQueries
  DNSQueryCount: DNSQueryCount
queryFrequency: 1d
requiredDataConnectors:
- connectorId: ASimDnsActivityLogs
  dataTypes:
  - ASimDnsActivityLogs
- connectorId: GCPDNSDataConnector
  dataTypes:
  - GCP_DNS_CL
- connectorId: AzureFirewall
  dataTypes:
  - AzureDiagnostics
- connectorId: CiscoUmbrellaDataConnector
  dataTypes:
  - Cisco_Umbrella_proxy_CL
- connectorId: Corelight
  dataTypes:
  - Corelight_CL
- connectorId: InfobloxNIOS
  dataTypes:
  - Syslog
- connectorId: NXLogDnsLogs
  dataTypes:
  - NXLog_DNS_Server_CL
- connectorId: DNS
  dataTypes:
  - DnsEvents
- connectorId: AIVectraStream
  dataTypes:
  - VectraStream_CL
- connectorId: WindowsForwardedEvents
  dataTypes:
  - WindowsEvents
- connectorId: Zscaler
  dataTypes:
  - CommonSecurityLog
- connectorId: ISCBind
  dataTypes:
  - Syslog
id: 77b7c820-5f60-4779-8bdb-f06e21add5f1
version: 1.0.0
name: Rare client observed with high reverse DNS lookup count - Static threshold based (ASIM DNS Solution)
kind: Scheduled
status: Available
relevantTechniques:
- T1590
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/DNS Essentials/Analytic Rules/RareClientObservedWithHighReverseDNSLookupCountStaticThresholdBased.yaml
queryPeriod: 10d
alertDetailsOverride:
  alertDescriptionFormat: |-
    Client identified as making high reverse DNS counts which could be carrying out reconnaissance or discovery activity.

    Reverse DNS lookup threshold is: '{{DNSQuerythreshold}}'

    Current reverse DNS lookup count from this client is : '{{DNSQueryCount}}'

    DNS queries requested by this client inlcude: '{{DNSQueries}}'    
  alertDisplayNameFormat: "[Static threshold] Rare client has been observed as making high reverse DNS lookup count  - client IP: '{{SrcIpAddr}}'"
severity: Medium
triggerOperator: gt
tactics:
- Reconnaissance
tags:
- Schema: ASimDns
  SchemaVersion: 0.1.6
description: |
    'This rule identifies clients with high reverse DNS counts, which could be carrying out reconnaissance or discovery activity. This helps in detecting the possible initial phases of an attack, like discovery and reconnaissance. \n\nIt utilizes [ASIM](https://aka.ms/AboutASIM) normalization and is applied to any source that supports the ASIM DNS schema.'
entityMappings:
- entityType: IP
  fieldMappings:
  - identifier: Address
    columnName: SrcIpAddr

ARM

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "parameters": {
    "workspace": {
      "type": "String"
    }
  },
  "resources": [
    {
      "id": "[concat(resourceId('Microsoft.OperationalInsights/workspaces/providers', parameters('workspace'), 'Microsoft.SecurityInsights'),'/alertRules/77b7c820-5f60-4779-8bdb-f06e21add5f1')]",
      "name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/77b7c820-5f60-4779-8bdb-f06e21add5f1')]",
      "type": "Microsoft.OperationalInsights/workspaces/providers/alertRules",
      "kind": "Scheduled",
      "apiVersion": "2022-11-01",
      "properties": {
        "displayName": "Rare client observed with high reverse DNS lookup count - Static threshold based (ASIM DNS Solution)",
        "description": "'This rule identifies clients with high reverse DNS counts, which could be carrying out reconnaissance or discovery activity. This helps in detecting the possible initial phases of an attack, like discovery and reconnaissance. \\n\\nIt utilizes [ASIM](https://aka.ms/AboutASIM) normalization and is applied to any source that supports the ASIM DNS schema.'\n",
        "severity": "Medium",
        "enabled": true,
        "query": "let threshold = materialize (_GetWatchlist('DNS_Solution_Monitoring_Configuration')\n  | where wl_RuleName == 'Rare client observed with high reverse DNS lookup'\n      and wl_Type == 'Detection'\n  | project toint(wl_Threshold));\nlet stime = 10d;\nlet etime = 1d;\nlet SearchDomain = dynamic([\"in-addr.arpa\"]);\n_Im_Dns(starttime=ago(etime), domain_has_any=SearchDomain)\n| summarize\n  StartTimeUtc = min(TimeGenerated),\n  EndTimeUtc = max(TimeGenerated),\n  DNSQueryCount=dcount(DnsQuery)\n  by SrcIpAddr\n| where DNSQueryCount > toscalar(threshold)\n| project StartTimeUtc, EndTimeUtc, SrcIpAddr, DNSQueryCount \n| join kind=leftanti (_Im_Dns(starttime=ago(stime), endtime=ago(etime), domain_has_any=SearchDomain)\n  | summarize DNSQueryCount=dcount(DnsQuery) by SrcIpAddr, bin(TimeGenerated, 1d)\n  | where DNSQueryCount > toscalar(threshold)\n  | project SrcIpAddr, DNSQueryCount\n  )\n  on SrcIpAddr\n| join kind=inner (_Im_Dns(starttime=ago(etime), domain_has_any=SearchDomain)\n  | summarize DNSQueries=make_set(DnsQuery, 1000) by SrcIpAddr)\n  on SrcIpAddr\n| extend DNSQuerythreshold = toint(toscalar(threshold))\n| project-away SrcIpAddr1\n",
        "queryFrequency": "P1D",
        "queryPeriod": "P10D",
        "triggerOperator": "GreaterThan",
        "triggerThreshold": 0,
        "suppressionDuration": "PT1H",
        "suppressionEnabled": false,
        "tactics": [
          "Reconnaissance"
        ],
        "techniques": [
          "T1590"
        ],
        "alertRuleTemplateName": "77b7c820-5f60-4779-8bdb-f06e21add5f1",
        "eventGroupingSettings": {
          "aggregationKind": "AlertPerResult"
        },
        "alertDetailsOverride": {
          "alertDescriptionFormat": "Client identified as making high reverse DNS counts which could be carrying out reconnaissance or discovery activity.\n\nReverse DNS lookup threshold is: '{{DNSQuerythreshold}}'\n\nCurrent reverse DNS lookup count from this client is : '{{DNSQueryCount}}'\n\nDNS queries requested by this client inlcude: '{{DNSQueries}}'",
          "alertDisplayNameFormat": "[Static threshold] Rare client has been observed as making high reverse DNS lookup count  - client IP: '{{SrcIpAddr}}'"
        },
        "customDetails": {
          "DNSQuerythreshold": "DNSQuerythreshold",
          "DNSQueries": "DNSQueries",
          "DNSQueryCount": "DNSQueryCount"
        },
        "entityMappings": [
          {
            "fieldMappings": [
              {
                "columnName": "SrcIpAddr",
                "identifier": "Address"
              }
            ],
            "entityType": "IP"
          }
        ],
        "tags": [
          {
            "Schema": "ASimDns",
            "SchemaVersion": "0.1.6"
          }
        ],
        "OriginalUri": "https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/DNS Essentials/Analytic Rules/RareClientObservedWithHighReverseDNSLookupCountStaticThresholdBased.yaml",
        "templateVersion": "1.0.0",
        "status": "Available"
      }
    }
  ]
}