Suspicious Office Child Process PowerShell Execution

SIGMA detection rule by Nikolai Kruchkov

Detects Microsoft Office applications spawning PowerShell with suspicious execution parameters frequently associated with phishing payloads, malware delivery, macro abuse, and post-exploitation activity.

title: Suspicious Office Child Process PowerShell Execution

id: a3d8c6f1-1c42-4d7d-a3b8-6f2a9f7e1c12

status: stable

description: Detects Microsoft Office applications spawning PowerShell with suspicious execution parameters frequently associated with phishing payloads, malware delivery, macro abuse, and post-exploitation activity.

author: Nikolai Kruchkov

date: 2026-06-02

references:
  - https://attack.mitre.org/techniques/T1204/
  - https://attack.mitre.org/techniques/T1059/001/

logsource:
  product: windows
  category: process_creation

detection:

  selection_parent:
    ParentImage|endswith:
      - '\WINWORD.EXE'
      - '\EXCEL.EXE'
      - '\POWERPNT.EXE'
      - '\OUTLOOK.EXE'

  selection_child:
    Image|endswith:
      - '\powershell.exe'
      - '\pwsh.exe'

  selection_flags:
    CommandLine|contains:
      - '-nop'
      - '-w hidden'
      - '-windowstyle hidden'
      - '-executionpolicy bypass'
      - '-ep bypass'
      - '-enc'
      - '-encodedcommand'

  condition: selection_parent and selection_child and selection_flags

falsepositives:
  - Internal automation frameworks
  - Approved administrative scripts
  - Enterprise software deployment tooling

level: high

tags:
  - attack.execution
  - attack.t1059.001
  - attack.initial_access

[[ currentRule.title && currentRule.title.length > 60 ? currentRule.title.slice(0, 60) + '…' : currentRule.title ]]

205caafd-05f5-4626-8714-88ca17db19b1

Propose edits, view related rules, and engage with the community through comments.

Executable code, not a declarative rule

This submission is arbitrary [[ currentRule.format ? currentRule.format.toUpperCase() : '' ]] code, not a declarative detection rule — review it as you would any script before running it, and note that it cannot be safely aggregated or auto-executed alongside YARA/Sigma/Suricata/CRS rules.

Rejected pattern present

[[ reason ]]

What does this mean?

Format & documentation suggestions

Not a security issue — this rule is valid and was accepted as-is. These are optional fields/conventions its own format recommends, mainly affecting its quality score and how well it documents itself for other reviewers.

[[ reason ]]

What do these messages mean?

[[ currentRule.title && currentRule.title.length > 60 ? currentRule.title.slice(0, 60) + '…' : currentRule.title ]]

[[ currentRule.title ]]

Community Discussion