Detect excessive NXDOMAIN DNS queries - Anomaly based (ASIM DNS Solution)

id: 02f23312-1a33-4390-8b80-f7cd4df4dea0
name: Detect excessive NXDOMAIN DNS queries - Anomaly based (ASIM DNS Solution)
description: |
  'This rule makes use of the series decompose anomaly method to generate an alert when client requests excessive amount of DNS queries to non-existent domains. This helps in identifying possible C2 communications. It utilizes [ASIM](https://aka.ms/AboutASIM) normalization and is applied to any source that supports the ASIM DNS schema.'
severity: Medium
status: Available 
tags:
  - Schema: ASimDns
    SchemaVersion: 0.1.6
requiredDataConnectors: []
queryFrequency: 1d
queryPeriod: 14d
triggerOperator: gt
triggerThreshold: 0
tactics:
  - CommandAndControl
relevantTechniques:
  - T1568
  - T1008
query: |
  let threshold = 2.5;
  let min_t = ago(14d);
  let max_t = now();
  let dt = 1d;
  let summarizationexist = (
    union isfuzzy=true 
        (
        DNS_Summarized_Logs_ip_CL
        | where EventTime_t > ago(1d) 
        | project v = int(2)
        ),
        (
        print int(1) 
        | project v = print_0
        )
    | summarize maxv = max(v)
    | extend sumexist = (maxv > 1)
    );
  let allData = union isfuzzy=true
        (
        (datatable(exists: int, sumexist: bool)[1, false]
        | join (summarizationexist) on sumexist)
        | join (
            _Im_Dns(responsecodename='NXDOMAIN', starttime=todatetime(min_t), endtime=max_t)
            | summarize Count=count() by SrcIpAddr, bin(TimeGenerated, 1h)
            | extend EventTime = TimeGenerated, Count = toint(Count), exists=int(1)
            )
            on exists
        | project-away exists, maxv, sum*
        ),
        (
        DNS_Summarized_Logs_ip_CL
        | where EventTime_t > min_t and EventResultDetails_s == 'NXDOMAIN'
        | summarize Count=toint(sum(count__d)) by SrcIpAddr=SrcIpAddr_s, bin(EventTime=EventTime_t, 1h)
        );
  allData
  | make-series EventCount=sum(Count) on EventTime from min_t to max_t step dt by SrcIpAddr
  | extend (anomalies, score, baseline) = series_decompose_anomalies(EventCount, threshold, -1, 'linefit')
  | mv-expand anomalies, score, baseline, EventTime, EventCount
  | extend
    anomalies = toint(anomalies),
    score = toint(score),
    baseline = toint(baseline),
    EventTime = todatetime(EventTime),
    Total = tolong(EventCount)
  | where EventTime >= ago(dt)
  | where score >= threshold * 2
  | join kind=inner(_Im_Dns(responsecodename='NXDOMAIN', starttime=ago(dt), endtime=max_t)
    | summarize DNSQueries = make_set(DnsQuery) by SrcIpAddr)
    on SrcIpAddr
  | project-away SrcIpAddr1
entityMappings:
  - entityType: IP
    fieldMappings:
      - identifier: Address
        columnName: SrcIpAddr
eventGroupingSettings:
  aggregationKind: AlertPerResult
customDetails:
  DNSQueries: DNSQueries
  AnomalyScore: score
  baseline: baseline
  Total: Total
alertDetailsOverride:
  alertDisplayNameFormat: "[Anomaly] Excessive NXDOMAIN DNS Queries has been detected from client IP: '{{SrcIpAddr}}'"
  alertDescriptionFormat: "This client is generating excessive amount of DNS queries for non-existent domains. This can be an indication of possible C2 communications.\n\nBaseline for 'NXDOMAIN' error count for this client: '{{baseline}}'\n\nCurrent 'NXDOMAIN' error count for this client: '{{Total}}'\n\nDNS queries requested by the client include:\n\n'{{DNSQueries}}'"
version: 1.0.2
kind: Scheduled