Windows Process Creation: Cmd Invokes PowerShell via Obfuscated Environment Variable Expansion

Alerts on cmd.exe command lines that use obfuscated environment-variable SET to execute PowerShell.

FreeReviewedSigma · High · v2

Product: windows
Category: process_creation
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 flags Windows command interpreter executions that use obfuscated environment variable expansion to construct and run PowerShell, matching a specific cmd /c or /r pattern containing a SET statement and encoded PowerShell invocation fragments. Such behavior matters because attackers often hide PowerShell payloads and reduce detection by dynamically building commands from environment variables. The detection relies on process creation telemetry, specifically the full CommandLine field for cmd.exe with the expected obfuscation characteristics.

Reporting behind it

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Windows Process Creation: Cmd Invokes PowerShell via Obfuscated Environment Variable Expansion

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-execution-via-obfuscated-cmd-set-environment-variables-27aec9c9

title: "Windows Process Creation: Cmd Invokes PowerShell via Obfuscated Environment Variable Expansion"
id: f36e3df0-0b36-46a9-aa05-cf1922d4ca72
status: test
description: This rule flags Windows command interpreter executions that use obfuscated environment variable expansion to construct and run PowerShell, matching a specific cmd /c or /r pattern containing a SET statement and encoded PowerShell invocation fragments. Such behavior matters because attackers often hide PowerShell payloads and reduce detection by dynamically building commands from environment variables. The detection relies on process creation telemetry, specifically the full CommandLine field for cmd.exe with the expected obfuscation characteristics.
references:
  - https://github.com/SigmaHQ/sigma/issues/1009
  - https://github.com/SigmaHQ/sigma/blob/master/rules/windows/process_creation/proc_creation_win_hktl_invoke_obfuscation_var.yml
author: Jonathan Cheong, oscd.community, Huntrule Team
date: 2020-10-15
modified: 2024-04-15
tags:
  - attack.stealth
  - attack.t1027
  - attack.execution
  - attack.t1059.001
logsource:
  category: process_creation
  product: windows
detection:
  selection:
    CommandLine|re: cmd.{0,5}(?:/c|/r)(?:\s|)\"set\s[a-zA-Z]{3,6}.*(?:\{\d\}){1,}\\\"\s+?\-f(?:.*\)){1,}.*\"
  condition: selection
falsepositives:
  - Unknown
level: high
license: DRL-1.1
related:
  - id: 27aec9c9-dbb0-4939-8422-1742242471d0
    type: derived

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