PowerShell Module: Obfuscated Environment Variable Expansion via cmd /c set -f Pattern

Alerts when PowerShell module payloads obfuscate execution via cmd /c|/r and environment-variable-based set patterns.

FreeReviewedSigma · High · v2

Product: windows
Category: ps_module
Author: Jonathan Cheong, oscd.community (SigmaHQ), DRL 1.1
Published: 2020-10-15
Updated: 2026-07-31

ATT&CK techniques

Execution → Defense Evasion

Recon
Resource Dev
Initial Access
Execution
- T1059.001PowerShell
Persistence
Priv Esc
Defense Evasion
- T1027Obfuscated Files or Information
Cred Access
Discovery
Lateral Movement
Collection
C2
Exfiltration
Impact

What it detects

This rule identifies PowerShell module activity where the command line payload matches an obfuscated pattern that invokes cmd /c or cmd /r and uses set with variable expansion formatted with -f. The behavior matters because attackers often hide execution details by combining environment variables, string formatting, and cmd-based execution to evade straightforward detection. It relies on PowerShell module telemetry that includes the Payload content for pattern matching against the cmd/set/-f and expansion structure.

Reporting behind it

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PowerShell Module: Obfuscated Environment Variable Expansion via cmd /c set -f Pattern

Pivot detection · T1027 · 9 related

Changelog

v2
Candidate ingested via manual entry.2026-07-31
v1
No changelog recorded for this version.2026-07-30

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.

windows-powershell-module-obfuscated-cmd-set-environment-variable-launcher-behav-6bfb8fa7

title: "PowerShell Module: Obfuscated Environment Variable Expansion via cmd /c set -f Pattern"
id: 59333121-79f0-4b8a-ac93-9559ac6e63ee
related:
  - id: 0adfbc14-0ed1-11eb-adc1-0242ac120002
    type: derived
  - id: 6bfb8fa7-b2e7-4f6c-8d9d-824e5d06ea9e
    type: derived
status: test
description: This rule identifies PowerShell module activity where the command line payload matches an obfuscated pattern that invokes cmd /c or cmd /r and uses set with variable expansion formatted with -f. The behavior matters because attackers often hide execution details by combining environment variables, string formatting, and cmd-based execution to evade straightforward detection. It relies on PowerShell module telemetry that includes the Payload content for pattern matching against the cmd/set/-f and expansion structure.
references:
  - https://github.com/SigmaHQ/sigma/issues/1009
  - https://github.com/SigmaHQ/sigma/blob/master/rules/windows/powershell/powershell_module/posh_pm_invoke_obfuscation_var.yml
author: Jonathan Cheong, oscd.community, Huntrule Team
date: 2020-10-15
modified: 2024-04-05
tags:
  - attack.stealth
  - attack.t1027
  - attack.execution
  - attack.t1059.001
logsource:
  product: windows
  category: ps_module
  definition: 0ad03ef1-f21b-4a79-8ce8-e6900c54b65b
detection:
  selection_4103:
    Payload|re: cmd.{0,5}(?:/c|/r)(?:\s|)"set\s[a-zA-Z]{3,6}.*(?:\{\d\}){1,}\\"\s+?-f(?:.*\)){1,}.*"
  condition: selection_4103
falsepositives:
  - Unknown
level: high
license: DRL-1.1

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