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

tags:
- SchemaVersion: 0.1.6
  Schema: ASimDns
requiredDataConnectors: []
relevantTechniques:
- T1590
triggerOperator: gt
customDetails:
  DNSQueryCount: DNSQueryCount
  DNSQueries: DNSQueries
  DNSQuerythreshold: DNSQuerythreshold
queryFrequency: 1d
severity: Medium
triggerThreshold: 0
entityMappings:
- fieldMappings:
  - columnName: SrcIpAddr
    identifier: Address
  entityType: IP
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}}'"
name: Rare client observed with high reverse DNS lookup count - Static threshold based (ASIM DNS Solution)
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  
version: 1.0.2
tactics:
- Reconnaissance
queryPeriod: 10d
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.'
kind: Scheduled
id: 77b7c820-5f60-4779-8bdb-f06e21add5f1
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/DNS Essentials/Analytic Rules/RareClientObservedWithHighReverseDNSLookupCountStaticThresholdBased.yaml
eventGroupingSettings:
  aggregationKind: AlertPerResult
status: Available

ARM