Potential DGA detected (ASIM DNS Schema)

Severity: medium
Time window: 10d
Group by: SrcIpAddr, dcount_sld
Author: Yaron
Source: github.com/Azure/Azure-Sentinel

'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). 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). This analytic rule uses ASIM and supports any built-in or custom source that supports the ASIM DNS schema'

MITRE ATT&CK coverage

Tactic	Techniques
Command & Control	`T1008` Fallback Channels, `T1568` Dynamic Resolution

Rule body kusto

id: 983a6922-894d-413c-9f04-d7add0ecc307
name: Potential DGA detected (ASIM DNS Schema)
description: |
  '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). 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).
  This analytic rule uses [ASIM](https://aka.ms/AboutASIM) and supports any built-in or custom source that supports the ASIM DNS schema'
severity: Medium
requiredDataConnectors:
  - connectorId: DNS
    dataTypes:
      - DnsEvents
  - connectorId: AzureFirewall
    dataTypes: 
      - AzureDiagnostics
  - connectorId: Zscaler
    dataTypes:
      - CommonSecurityLog
  - connectorId: InfobloxNIOS
    dataTypes: 
      - Syslog
  - connectorId: GCPDNSDataConnector
    dataTypes: 
      - GCP_DNS_CL
  - connectorId: NXLogDnsLogs
    dataTypes: 
      - NXLog_DNS_Server_CL
  - connectorId: CiscoUmbrellaDataConnector
    dataTypes: 
      - Cisco_Umbrella_dns_CL
  - connectorId: Corelight
    dataTypes: 
      - Corelight_CL

queryFrequency: 1d
queryPeriod: 10d
triggerOperator: gt
triggerThreshold: 0
tactics:
  - CommandAndControl
relevantTechniques:
  - T1568
  - T1008
tags:
  - ParentAlert: https://github.com/Azure/Azure-Sentinel/blob/master/Detections/DnsEvents/DNS_HighNXDomainCount_detection.yaml
    version: 1.0.0
  - Schema: ASIMDns
    SchemaVersion: 0.1.1
query: |
  let referencestarttime = 10d;
  let referenceendtime = 1d;
  let threshold = 100;
  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())
    | extend sld = tostring(split(DnsQuery, ".")[-2])
    | summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated), dcount(sld) by SrcIpAddr
    | where dcount_sld > threshold
    // Filter out previously seen IPs
    | join kind=leftanti (nxDomainDnsEvents (stime=ago(referencestarttime), etime=ago(referenceendtime))
      | extend sld = tostring(split(DnsQuery, ".")[-2])
      | summarize dcount(sld) by SrcIpAddr
      | where dcount_sld > threshold ) on SrcIpAddr
  // Pull out sample NXDomain responses for those remaining potentially infected IPs
  | join kind = inner (nxDomainDnsEvents (stime=ago(referencestarttime), etime=now()) | summarize by DnsQuery, SrcIpAddr) on SrcIpAddr
  | summarize StartTime = min(StartTime), EndTime = max(EndTime), sampleNXDomainList=make_list(DnsQuery, 100)  by SrcIpAddr, dcount_sld
entityMappings:
  - entityType: IP
    fieldMappings:
      - identifier: Address
        columnName: SrcIpAddr
version: 1.3.4
kind: Scheduled
metadata:
    source:
        kind: Community
    author:
        name: Yaron
    support:
        tier: Community
    categories:
        domains: [ "Security - Network" ]

Stages and Predicates

Parameters

let referencestarttime = 10d;
let referenceendtime = 1d;
let threshold = 100;

The stages below define let nxDomainDnsEvents (the rule's main pipeline source).

Stage 1: `source`

_Im_Dns

Stage 2: `where`

where DnsQueryTypeName in~ ("A", "AAAA")

Stage 3: `where`

where not (ipv4_is_in_range(SrcIpAddr, "127.0.0.1"))

Stage 4: `where`

where not (DnsQuery contains "/") and DnsQuery contains "."

The stages below run on nxDomainDnsEvents (the outer pipeline).

Stage 5: `extend`

extend sld

Stage 6: `summarize`

summarize EndTime, StartTime by SrcIpAddr

Stage 7: `where`

where dcount_sld > 100

Stage 8: `join` (negated)

join kind=leftanti (...)

Stage 9: `join`

join kind=inner (...)

Stage 10: `summarize`

summarize EndTime, StartTime, sampleNXDomainList by SrcIpAddr, dcount_sld

Exclusions

Top-level NOT(...) conjuncts: predicates this rule actively suppresses.

Field	Kind	Excluded values
`SrcIpAddr`	cidr_match	`127.0.0.1`
`DnsQuery`	contains	`/`
`dcount_sld`	gt	`100`

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

Field	Kind	Values
`DnsQuery`	contains	`.`
`DnsQueryTypeName`	in	`A` transforms: `cased` `AAAA` transforms: `cased`
`dcount_sld`	gt	`100` transforms: `cased`

Output fields

Fields the rule emits when it matches. Chronicle authors list these in the outcome block; they appear on the detection and $risk_score drives alerting. Sentinel / Defender XDR rules build them up through project / summarize / extend stages. Sentinel maps these into alert fields via entityMappings and customDetails; Defender XDR custom detections surface them as alert fields directly.

Field	Source
`EndTime`	`summarize`
`SrcIpAddr`	`summarize`
`StartTime`	`summarize`
`dcount_sld`	`summarize`
`sampleNXDomainList`	`summarize`

`j` / `k`	Scroll down / up
`d` / `u`	Half-page down / up
`gg` / `G`	Top / bottom
`h` / `l`	History back / forward
`f`	Follow link (`Shift` = new tab)
`/`	Focus search
`?`	Toggle this help
`↑` / `↓`	Navigate search results
`Enter`	Open highlighted result
`Esc`	Close results / dialog

`type:`	`events` / `rules` / `providers`
`vendor:`	`sigma` / `elastic` / `splunk` / `kusto` / `chronicle` (vendor name alone also works: `sigma:`, `kql:`, `secops:`…)
`tactic:`	TA-id, slug, or name: `credential_access`, `TA0006`
`technique:`	technique or sub-technique ID: `T1003`, `T1003.001` (alias `tech:`)
`severity:`	`critical` / `high` / `medium` / `low` / `informational` (alias `sev:`)
`risk_score`	Numeric comparison on the Elastic risk score (0 to 100): `risk_score>50`, `risk_score<=20`, `risk_score=99` (alias `risk`; Elastic rules only)
`stages:`	Rules with exactly N pipeline stages
`correlation:`	`single_event` / `sequence` / `alternatives` / `alternatives_cross_log` / `all_required` / `correlated`
`with:`	Co-occurrence event-id; stacks (`with:4624 with:4769`) to require all, while a comma list in one occurrence (`with:4624,4769`) is an either-or group. Implies multi-event
`like:`	Structural neighbors of a rule slug (equivalents + subsumption stricter / broader): `like:comsvcs_lsass_memory_dump-splunk-sysmon`
`groupby:`	Entity-grouping substring match against `group_by_keys`: `groupby:user`, `groupby:host`
`uses:`	Rules whose predicate tree touches the field (any kind, any value): `uses:CommandLine`
`excludes:`	Rules with top-level `not()` clauses on the field (FP whitelists): `excludes:ParentImage`
`field:` / `value:`	Predicate search; narrows rule cards to those with a matching leaf and drives the indicator tier. Unquoted = substring, wildcards allowed (`value:mimikatz`)
`indicator:`	Shorthand for `field:F value:V`: `indicator:Image=*\powershell.exe`
`kind:`	Filter by predicate kind. Narrows rule cards to those carrying a matching predicate leaf (`vendor:elastic kind:cidr_match`) and drives the indicator tier: `contains` / `starts_with` / `ends_with` / `regex` / `cidr` / `eq` / `in` … (operator aliases `op:`/`match:`)
`has:` / `no:`	`sample`, `field`, `notes`, `refs`, `trace`, `thirdparty`, `rule`, `pattern`, `timewindow`, `threshold`, `newterms`, `sigma`/`elastic`/`splunk`/`kusto`/`chronicle`
`-op:val`	Exclude matches; works on most operators but not `type:`/`like:`/`has:`/`no:` (use `no:<flag>` to exclude a rule flag): `tactic:execution -vendor:splunk`. Standalone `-kind:`/`-field:`/`-value:` drop every rule carrying a matching predicate leaf (`type:rules -kind:is_null`)
`field:"…"` / `value:"…"`	Quoted value = anchored exact match (also allows spaces): `value:"net user"`
`a,b`	Comma = OR inside one operator (`vendor:sigma,elastic`, `severity:high,critical`); repeating a facet merges the same way. `field:`/`value:` never split (literal commas)
`vendors:` / `stage:`	Singular and plural spellings fold to the canonical operator and value: `tactics:` = `tactic:`, `type:event` = `type:events`, `correlation:sequences` = `correlation:sequence`, `has:thresholds` = `has:threshold`
`"quoted phrase"`	Exact-match a multi-word phrase (free text)

Potential DGA detected (ASIM DNS Schema)

MITRE ATT&CK coverage

Rule body kusto

Stages and Predicates

Parameters

Stage 1: `source`

Stage 2: `where`

Stage 3: `where`

Stage 4: `where`

Stage 5: `extend`

Stage 6: `summarize`

Stage 7: `where`

Stage 8: `join` (negated)

Stage 9: `join`

Stage 10: `summarize`

Exclusions

Indicators

Output fields

Keyboard shortcuts

Search operators

Potential DGA detected (ASIM DNS Schema)

MITRE ATT&CK coverage

Rule body kusto

Stages and Predicates

Parameters

Stage 1: source

Stage 2: where

Stage 3: where

Stage 4: where

Stage 5: extend

Stage 6: summarize

Stage 7: where

Stage 8: join (negated)

Stage 9: join

Stage 10: summarize

Exclusions

Indicators

Output fields

Stage 1: `source`

Stage 2: `where`

Stage 3: `where`

Stage 4: `where`

Stage 5: `extend`

Stage 6: `summarize`

Stage 7: `where`

Stage 8: `join` (negated)

Stage 9: `join`

Stage 10: `summarize`