Fake computer account created

Severity: medium
Time window: 1h
Group by: Computer, SubjectAccount, SubjectDomainName, SubjectLogonId, SubjectUserName, SubjectUserSid, TargetAccount, TargetDomainName, TargetSid, TargetUserName, UserPrincipalName
Author: Vasileios Paschalidis
Source: github.com/Azure/Azure-Sentinel

This query detects domain user accounts creation (event ID 4720) where the username ends with $. Accounts that end with $ are normally domain computer accounts and when they are created the event ID 4741 is generated instead.

MITRE ATT&CK coverage

Tactic	Techniques
Stealth	`T1564` Hide Artifacts

Event coverage

Provider	Event	Title
Security-Auditing	Event ID 4720	A user account was created.

Rule body kusto

id: c1faf5e8-6958-11ec-90d6-0242ac120003
name: Fake computer account created
description: |
   'This query detects domain user accounts creation (event ID 4720) where the username ends with $. 
   Accounts that end with $ are normally domain computer accounts and when they are created the event ID 4741 is generated instead.'
severity: Medium
requiredDataConnectors:
  - connectorId: SecurityEvents
    dataTypes:
      - SecurityEvent
queryFrequency: 1h
queryPeriod: 1h
triggerOperator: gt
triggerThreshold: 0
tactics:
  - DefenseEvasion
relevantTechniques:
  - T1564
query: |
  SecurityEvent
  | where EventID == 4720 and TargetUserName endswith "$"
  | summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated) by Computer, SubjectUserName, SubjectDomainName, SubjectAccount, SubjectUserSid, SubjectLogonId, 
  TargetUserName, TargetDomainName, TargetAccount, TargetSid, UserPrincipalName
  | extend HostName = tostring(split(Computer, ".")[0]), DomainIndex = toint(indexof(Computer, '.'))
  | extend HostNameDomain = iff(DomainIndex != -1, substring(Computer, DomainIndex + 1), Computer)
  | project-away DomainIndex
entityMappings:
  - entityType: Account
    fieldMappings:
      - identifier: FullName
        columnName: SubjectAccount
      - identifier: Name
        columnName: SubjectUserName
      - identifier: NTDomain
        columnName: SubjectDomainName
  - entityType: Account
    fieldMappings:
      - identifier: Sid
        columnName: SubjectUserSid
  - entityType: Account
    fieldMappings:
      - identifier: FullName
        columnName: TargetAccount
      - identifier: Name
        columnName: TargetUserName
      - identifier: NTDomain
        columnName: TargetDomainName
  - entityType: Account
    fieldMappings:
      - identifier: Sid
        columnName: TargetSid
  - entityType: Host
    fieldMappings:
      - identifier: FullName
        columnName: Computer
      - identifier: HostName
        columnName: HostName
      - identifier: DnsDomain
        columnName: HostNameDomain
version: 1.0.4
kind: Scheduled
metadata:
    source:
        kind: Community
    author:
        name: Vasileios Paschalidis
    support:
        tier: Community
    categories:
        domains: [ "Security - Others" ]

Stages and Predicates

Stage 1: `source`

SecurityEvent

Stage 2: `where`

| where EventID == 4720 and TargetUserName endswith "$"

Stage 3: `summarize`

| summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated) by Computer, SubjectUserName, SubjectDomainName, SubjectAccount, SubjectUserSid, SubjectLogonId, 
TargetUserName, TargetDomainName, TargetAccount, TargetSid, UserPrincipalName

Stage 4: `extend`

| extend HostName = tostring(split(Computer, ".")[0]), DomainIndex = toint(indexof(Computer, '.'))

Stage 5: `extend`

| extend HostNameDomain = iff(DomainIndex != -1, substring(Computer, DomainIndex + 1), Computer)

HostNameDomain =

ifDomainIndex != -1substring(Computer, (DomainIndex + 1))

elseComputer

Stage 6: `project-away`

| project-away DomainIndex

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
`EventID`	eq	`4720` transforms: `cased` corpus 5 (kusto 3, splunk 2)
`TargetUserName`	ends_with	`$` corpus 7 (sigma 5, kusto 2)

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
`Computer`	`summarize`
`EndTime`	`summarize`
`StartTime`	`summarize`
`SubjectAccount`	`summarize`
`SubjectDomainName`	`summarize`
`SubjectLogonId`	`summarize`
`SubjectUserName`	`summarize`
`SubjectUserSid`	`summarize`
`TargetAccount`	`summarize`
`TargetDomainName`	`summarize`
`TargetSid`	`summarize`
`TargetUserName`	`summarize`
`UserPrincipalName`	`summarize`
`HostName`	`extend`
`HostNameDomain`	`extend`

`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)

Fake computer account created

MITRE ATT&CK coverage

Event coverage

Rule body kusto

Stages and Predicates

Stage 1: `source`

Stage 2: `where`

Stage 3: `summarize`

Stage 4: `extend`

Stage 5: `extend`

Stage 6: `project-away`

Indicators

Output fields

Keyboard shortcuts

Search operators

Fake computer account created

MITRE ATT&CK coverage

Event coverage

Rule body kusto

Stages and Predicates

Stage 1: source

Stage 2: where

Stage 3: summarize

Stage 4: extend

Stage 5: extend

Stage 6: project-away

Indicators

Output fields

Stage 1: `source`

Stage 2: `where`

Stage 3: `summarize`

Stage 4: `extend`

Stage 5: `extend`

Stage 6: `project-away`