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. It utilizes ASIM normalization and is applied to any source that supports the ASIM DNS schema.
Severity	Medium
Tactics	Reconnaissance
Techniques	T1590
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	1.0.2
Arm template	77b7c820-5f60-4779-8bdb-f06e21add5f1.json

KQL

let threshold = 10;
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 > 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 > 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 = threshold
| project-away SrcIpAddr1

YAML

triggerOperator: gt
tags:
- SchemaVersion: 0.1.6
  Schema: ASimDns
requiredDataConnectors: []
relevantTechniques:
- T1590
entityMappings:
- entityType: IP
  fieldMappings:
  - identifier: Address
    columnName: SrcIpAddr
query: |
  let threshold = 10;
  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 > 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 > 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 = threshold
  | project-away SrcIpAddr1  
triggerThreshold: 0
customDetails:
  DNSQuerythreshold: DNSQuerythreshold
  DNSQueryCount: DNSQueryCount
  DNSQueries: DNSQueries
alertDetailsOverride:
  alertDisplayNameFormat: "[Static threshold] Rare client has been observed as making high reverse DNS lookup count  - client IP: '{{SrcIpAddr}}'"
  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}}'    
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/DNS Essentials/Analytic Rules/RareClientObservedWithHighReverseDNSLookupCountStaticThresholdBased.yaml
queryPeriod: 10d
tactics:
- Reconnaissance
name: Rare client observed with high reverse DNS lookup count - Static threshold based (ASIM DNS Solution)
status: Available
kind: Scheduled
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. It utilizes [ASIM](https://aka.ms/AboutASIM) normalization and is applied to any source that supports the ASIM DNS schema.'
id: 77b7c820-5f60-4779-8bdb-f06e21add5f1
version: 1.0.2
eventGroupingSettings:
  aggregationKind: AlertPerResult
queryFrequency: 1d
severity: Medium

ARM