PowerShell: Obfuscated IEX Invocation via Invoke-Obfuscation String/Variable Patterns

Alerts on obfuscated PowerShell IEX invocation strings built from Invoke-Obfuscation style concatenation patterns in ScriptBlockText.

FreeReviewedSigma · High · v2

Product: windows
Category: ps_script
Author: Daniel Bohannon (@Mandiant/@FireEye), oscd.community (SigmaHQ), DRL 1.1
Published: 2019-11-08
Updated: 2026-07-31

Analysis Detection

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 PowerShell script block content that matches characteristic patterns used to obfuscate variables and strings in an IEX (Invoke-Expression) invocation. Attackers rely on obfuscation to evade inspection while still executing dynamically constructed code. The detection depends on Script Block Logging telemetry that captures ScriptBlockText for matching regular expressions.

Reporting behind it

Related detections9 linkedT1027 — drag to rearrange

Suspicious PowerShell Invoke-Expression with Replace Obfuscation

Malicious Emmenhtal JavaScript Loader Spawning Encoded PowerShell

Suspicious Python Interpreter Launching Encoded PowerShell via subprocess

Suspicious PS1Bot PowerShell Payload Written to ProgramData (via file_event)

Malicious Non-Interactive Encoded PowerShell Stager (via process_creation)

Suspicious Hidden PowerShell Executing Substring of Dropped File

PowerShell Encoded or Download-Cradle Command Line (via process_creation)

Obfuscated Encoded PowerShell Payload Deployed - PowerShell (via powershell)

Suspicious PowerShell AES Decryption and Reflective Method Invocation in SolarMarker

PowerShell: Obfuscated IEX Invocation via Invoke-Obfuscation String/Variable Patterns

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.

powershell-iex-obfuscated-invocation-indicators-from-invoke-obfuscation-patterns-1b9dc62e

title: "PowerShell: Obfuscated IEX Invocation via Invoke-Obfuscation String/Variable Patterns"
id: 42ab965e-b209-450d-88e5-9a1c8e0c0f85
status: test
description: This rule flags PowerShell script block content that matches characteristic patterns used to obfuscate variables and strings in an IEX (Invoke-Expression) invocation. Attackers rely on obfuscation to evade inspection while still executing dynamically constructed code. The detection depends on Script Block Logging telemetry that captures ScriptBlockText for matching regular expressions.
references:
  - https://github.com/danielbohannon/Invoke-Obfuscation/blob/f20e7f843edd0a3a7716736e9eddfa423395dd26/Out-ObfuscatedStringCommand.ps1#L873-L888
  - https://github.com/SigmaHQ/sigma/blob/master/rules/windows/powershell/powershell_script/posh_ps_invoke_obfuscation_obfuscated_iex.yml
author: Daniel Bohannon (@Mandiant/@FireEye), oscd.community, Huntrule Team
date: 2019-11-08
modified: 2022-12-31
tags:
  - attack.stealth
  - attack.t1027
  - attack.execution
  - attack.t1059.001
logsource:
  product: windows
  category: ps_script
  definition: "Requirements: Script Block Logging must be enabled"
detection:
  selection_iex:
    - ScriptBlockText|re: \$PSHome\[\s*\d{1,3}\s*\]\s*\+\s*\$PSHome\[
    - ScriptBlockText|re: \$ShellId\[\s*\d{1,3}\s*\]\s*\+\s*\$ShellId\[
    - ScriptBlockText|re: \$env:Public\[\s*\d{1,3}\s*\]\s*\+\s*\$env:Public\[
    - ScriptBlockText|re: \$env:ComSpec\[(\s*\d{1,3}\s*,){2}
    - ScriptBlockText|re: \*mdr\*\W\s*\)\.Name
    - ScriptBlockText|re: \$VerbosePreference\.ToString\(
  condition: selection_iex
falsepositives:
  - Unknown
level: high
license: DRL-1.1
related:
  - id: 1b9dc62e-6e9e-42a3-8990-94d7a10007f7
    type: derived

Convert

This rule as a query you can run. Uses no unlock credit.

SplunkSPL