Potential DGADomain Generation Algorithm detected via Repetitive Failures - Static threshold based ASIM DNS Solution

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Id	89ba52fa-96a7-4653-829a-ca49bb13336c
Rulename	Potential DGA(Domain Generation Algorithm) detected via Repetitive Failures - Static threshold based (ASIM DNS Solution)
Description	This rule 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). An 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). It utilizes ASIM normalization and is applied to any source that supports the ASIM DNS schema.
Severity	Medium
Tactics	CommandAndControl
Techniques	T1568 T1008
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/PotentialDGADetectedviaRepetitiveFailuresStaticThresholdBased.yaml
Version	1.0.2
Arm template	89ba52fa-96a7-4653-829a-ca49bb13336c.json

KQL

let threshold = 100;
let lookback = 10d;
let referenceendtime = 1d;
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())
| summarize
  StartTimeUtc = min(TimeGenerated),
  EndTimeUtc = max(TimeGenerated),
  DNSQueryCount=dcount(DnsQuery)
  by SrcIpAddr
| where DNSQueryCount > threshold
// Filter out previously seen IPs
| join kind=leftanti (nxDomainDnsEvents (stime=ago(lookback), etime=ago(referenceendtime))
  | summarize DNSQueryCount=dcount(DnsQuery) by SrcIpAddr, bin(TimeGenerated,1d)
  | where DNSQueryCount > threshold)
  on SrcIpAddr
// Pull out sample NXDomain responses for those remaining potentially infected IPs
| join kind = inner (nxDomainDnsEvents (stime=ago(lookback), etime=now())
  | summarize by DnsQuery, SrcIpAddr)
  on SrcIpAddr
| summarize
  StartTimeUtc = min(StartTimeUtc),
  EndTimeUtc = max(EndTimeUtc),
  DNSQueries=make_list(DnsQuery, 100)
  by SrcIpAddr, DNSQueryCount
| extend DNSQueryThreshold=threshold

YAML

customDetails:
  DNSQueryThreshold: DNSQueryThreshold
  DNSQueries: DNSQueries
  DNSQueryCount: DNSQueryCount
status: Available
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/DNS Essentials/Analytic Rules/PotentialDGADetectedviaRepetitiveFailuresStaticThresholdBased.yaml
alertDetailsOverride:
  alertDisplayNameFormat: "[Static threshold] Potential DGA (Domain Generation Algorithm) originating from client IP: '{{SrcIpAddr}}' has been detected."
  alertDescriptionFormat: |-
    Client has been identified with high NXDomain count which could be indicative of a DGA (cycling through possible C2 domains where most C2s are not live). This client is found to be communicating with multiple Domains which do not exist.

    DGA DNS query count baseline is: '{{DNSQueryThreshold}}'

    Current failed DNS query count from this client: '{{DNSQueryCount}}'

    DNS queries requested by this client inlcude: '{{DNSQueries}}'    
query: |
  let threshold = 100;
  let lookback = 10d;
  let referenceendtime = 1d;
  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())
  | summarize
    StartTimeUtc = min(TimeGenerated),
    EndTimeUtc = max(TimeGenerated),
    DNSQueryCount=dcount(DnsQuery)
    by SrcIpAddr
  | where DNSQueryCount > threshold
  // Filter out previously seen IPs
  | join kind=leftanti (nxDomainDnsEvents (stime=ago(lookback), etime=ago(referenceendtime))
    | summarize DNSQueryCount=dcount(DnsQuery) by SrcIpAddr, bin(TimeGenerated,1d)
    | where DNSQueryCount > threshold)
    on SrcIpAddr
  // Pull out sample NXDomain responses for those remaining potentially infected IPs
  | join kind = inner (nxDomainDnsEvents (stime=ago(lookback), etime=now())
    | summarize by DnsQuery, SrcIpAddr)
    on SrcIpAddr
  | summarize
    StartTimeUtc = min(StartTimeUtc),
    EndTimeUtc = max(EndTimeUtc),
    DNSQueries=make_list(DnsQuery, 100)
    by SrcIpAddr, DNSQueryCount
  | extend DNSQueryThreshold=threshold  
requiredDataConnectors: []
relevantTechniques:
- T1568
- T1008
kind: Scheduled
name: Potential DGA(Domain Generation Algorithm) detected via Repetitive Failures - Static threshold based (ASIM DNS Solution)
tactics:
- CommandAndControl
severity: Medium
entityMappings:
- fieldMappings:
  - identifier: Address
    columnName: SrcIpAddr
  entityType: IP
tags:
- Schema: ASimDns
  SchemaVersion: 0.1.6
queryFrequency: 1d
description: |
    'This rule 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). An 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). It utilizes [ASIM](https://aka.ms/AboutASIM) normalization and is applied to any source that supports the ASIM DNS schema.'
eventGroupingSettings:
  aggregationKind: AlertPerResult
triggerThreshold: 0
triggerOperator: gt
version: 1.0.2
queryPeriod: 10d
id: 89ba52fa-96a7-4653-829a-ca49bb13336c

ARM