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Detection rules › Kusto

Suspicious parentprocess relationship - Office child processes.

Status
available
Severity
medium
Time window
1h
Source
github.com/Azure/Azure-Sentinel

The attacker sends a spearphishing email to a user. The email contains a link, which points to a website that eventually presents the user a download of an MS Office document. This document contains a malicious macro. The macro spawns a new child process providing initial access. This detection looks for suspicious parent-process chains starting with a browser which spawns an Office application which spawns something else.

MITRE ATT&CK coverage

TacticTechniques
Initial AccessT1566.002 Phishing: Spearphishing Link

Event coverage

ProviderEvent/ActionTypeTitle
SysmonEvent ID 1Process creation
Security-AuditingEvent ID 4688A new process has been created.
Defender-DeviceProcessEventsanyProcess activity (any)

Rule body kusto

id: 5ee34fa1-64ed-48c7-afa2-794b244f6c60
name: Suspicious parentprocess relationship - Office child processes. 
description: |
  The attacker sends a spearphishing email to a user. The email contains a link, which points to a website that eventually presents the user a download of an MS Office document. This document contains a malicious macro. The macro spawns a new child process providing initial access. This detection looks for suspicious parent-process chains starting with a browser which spawns an Office application which spawns something else.
severity: Medium
status: Available
requiredDataConnectors:
  - connectorId: MicrosoftThreatProtection
    dataTypes:
      - DeviceProcessEvents
queryFrequency: 1h
queryPeriod: 1h
triggerOperator: gt
triggerThreshold: 0
tactics:
  - InitialAccess
relevantTechniques:
  - T1566.002
query: |
  let browsers = dynamic(["iexplore.exe", "chrome.exe", "firefox.exe", "msedge.exe"]); // Customize this list for your environment.
  let officeApps = dynamic(["winword.exe", "excel.exe", "powerpnt.exe"]); // Consider adding other Office applications such as Publisher, Visio and Access. 
  // This is an allow-list of the most common child processes. This is a quick and dirty solution. Consider allow-listing the full process path instead of file name.
  // Also, make this list as short as possible. Remove anything from this list if it doesn't occur in your organization. 
  let allowList = dynamic(["MSOSYNC.exe", "splwow64.exe", "csc.exe", "outlook.exe", "AcroRd32.exe", "Acrobat.exe", "explorer.exe", "DW20.exe", 
  "Microsoft.Mashup.Container.Loader.exe", "Microsoft.Mashup.Container.NetFX40.exe", "WerFault.exe", "CLVIEW.exe"]); 
  DeviceProcessEvents
  | where InitiatingProcessParentFileName in~ (browsers) and InitiatingProcessFileName in~ (officeApps) and 
  FileName !in~ (officeApps) and FileName !in~ (browsers) and FileName !in~ (allowList)
  | project-rename ProcessStart_Timestamp = Timestamp
entityMappings:
  - entityType: Host
    fieldMappings:
      - identifier: FullName
        columnName: DeviceName
  - entityType: Account
    fieldMappings:
      - identifier: Sid
        columnName: AccountSid 
      - identifier: Name
        columnName: AccountName
      - identifier: NTDomain
        columnName: AccountDomain
  - entityType: Process
    fieldMappings:
      - identifier: CommandLine
        columnName: ProcessCommandLine
version: 1.0.1
kind: Scheduled

Stages and Predicates

Parameters

let browsers = dynamic(["iexplore.exe", "chrome.exe", "firefox.exe", "msedge.exe"]);
let officeApps = dynamic(["winword.exe", "excel.exe", "powerpnt.exe"]);

Let binding: allowList

let allowList = dynamic(["MSOSYNC.exe", "splwow64.exe", "csc.exe", "outlook.exe", "AcroRd32.exe", "Acrobat.exe", "explorer.exe", "DW20.exe", 
"Microsoft.Mashup.Container.Loader.exe", "Microsoft.Mashup.Container.NetFX40.exe", "WerFault.exe", "CLVIEW.exe"]);

Stage 1: source

DeviceProcessEvents

Stage 2: where

| where InitiatingProcessParentFileName in~ (browsers) and InitiatingProcessFileName in~ (officeApps) and 
FileName !in~ (officeApps) and FileName !in~ (browsers) and FileName !in~ (allowList)

References allowList (defined above).

Stage 3: project-rename

| project-rename ProcessStart_Timestamp = Timestamp

Exclusions

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

FieldKindExcluded values
FileNameinAcroRd32.exe, Acrobat.exe, CLVIEW.exe, DW20.exe, MSOSYNC.exe, Microsoft.Mashup.Container.Loader.exe, Microsoft.Mashup.Container.NetFX40.exe, WerFault.exe, csc.exe, explorer.exe, outlook.exe, splwow64.exe
FileNameinchrome.exe, firefox.exe, iexplore.exe, msedge.exe
FileNameinexcel.exe, powerpnt.exe, winword.exe

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
InitiatingProcessFileNamein
  • excel.exe corpus 8 (elastic 8)
  • powerpnt.exe corpus 7 (elastic 7)
  • winword.exe corpus 8 (elastic 8)
InitiatingProcessParentFileNamein
  • chrome.exe
  • firefox.exe
  • iexplore.exe
  • msedge.exe

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
ProcessStart_Timestampproject-rename