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

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Id77b7c820-5f60-4779-8bdb-f06e21add5f1
RulenameRare client observed with high reverse DNS lookup count - Static threshold based (ASIM DNS Solution)
DescriptionThis 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.
SeverityMedium
TacticsReconnaissance
TechniquesT1590
Required data connectorsAIVectraStream
ASimDnsActivityLogs
AzureFirewall
CiscoUmbrellaDataConnector
Corelight
DNS
GCPDNSDataConnector
InfobloxNIOS
ISCBind
NXLogDnsLogs
WindowsForwardedEvents
Zscaler
KindScheduled
Query frequency1d
Query period10d
Trigger threshold0
Trigger operatorgt
Source Urihttps://github.com/Azure/Azure-Sentinel/blob/master/Solutions/DNS Essentials/Analytic Rules/RareClientObservedWithHighReverseDNSLookupCountStaticThresholdBased.yaml
Version1.0.0
Arm template77b7c820-5f60-4779-8bdb-f06e21add5f1.json
Deploy To Azure
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
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
{
  "$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"
      }
    }
  ]
}