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Detection rules › Kusto

NRT Base64 Encoded Windows Process Command-lines

Status
available
Severity
medium
Source
github.com/Azure/Azure-Sentinel

This detection identifies instances of a base64 encoded PE file header seen in the process command line parameter.

MITRE ATT&CK coverage

TacticTechniques
ExecutionT1059 Command and Scripting Interpreter
StealthT1027 Obfuscated Files or Information, T1140 Deobfuscate/Decode Files or Information

Event coverage

ProviderEventTitle
Security-AuditingEvent ID 4688A new process has been created.

Rule body kusto

id: c3e5dbaa-a540-408c-8b36-68bdfb3df088
name: NRT Base64 Encoded Windows Process Command-lines
description: |
  'This detection identifies instances of a base64 encoded PE file header seen in the process command line parameter.'
severity: Medium
status: Available
requiredDataConnectors:
  - connectorId: SecurityEvents
    dataTypes:
      - SecurityEvent
  - connectorId: WindowsSecurityEvents
    dataTypes:
      - SecurityEvent
tactics:
  - Execution
  - DefenseEvasion
relevantTechniques:
  - T1059
  - T1027
  - T1140
query: |
 SecurityEvent
  | where EventID == 4688
  | where isnotempty(CommandLine)
  | where CommandLine contains "TVqQAAMAAAAEAAA"
  | extend HostName = tostring(split(Computer, '.', 0)[0]), DnsDomain = tostring(strcat_array(array_slice(split(Computer, '.'), 1, -1), '.'))
entityMappings:
  - entityType: Account
    fieldMappings:
      - identifier: FullName
        columnName: SubjectAccount
      - identifier: Name
        columnName: SubjectUserName
      - identifier: NTDomain
        columnName: SubjectDomainName
  - entityType: Host
    fieldMappings:
      - identifier: FullName
        columnName: Computer
      - identifier: HostName
        columnName: HostName
      - identifier: DnsDomain
        columnName: DnsDomain
version: 1.0.2
kind: NRT

Stages and Predicates

Stage 1: source

SecurityEvent

Stage 2: where

| where EventID == 4688

Stage 3: where

| where isnotempty(CommandLine)

Stage 4: where

| where CommandLine contains "TVqQAAMAAAAEAAA"

Stage 5: extend

| extend HostName = tostring(split(Computer, '.', 0)[0]), DnsDomain = tostring(strcat_array(array_slice(split(Computer, '.'), 1, -1), '.'))

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.

FieldKindValues
CommandLinecontains
  • TVqQAAMAAAAEAAA corpus 3 (kusto 3)
CommandLineis_not_null
  • (no value, null check)
EventIDeq
  • 4688 transforms: cased corpus 313 (splunk 283, kusto 30)

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.

FieldSource
DnsDomainextend
HostNameextend