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Detection rules › Sigma

Invoke-Obfuscation Obfuscated IEX Invocation

Status
test
Severity
high
Log source
category process_creation, product windows
Author
Daniel Bohannon (@Mandiant/@FireEye), oscd.community
Source
github.com/SigmaHQ/sigma

Detects all variations of obfuscated powershell IEX invocation code generated by Invoke-Obfuscation framework from the following code block

MITRE ATT&CK coverage

TacticTechniques
Execution
Stealth

Telemetry coverage

ProviderRecord / event type
SysmonEvent ID 1: Process creation
Security-AuditingEvent ID 4688: A new process has been created.

Rule body

title: Invoke-Obfuscation Obfuscated IEX Invocation
id: 4bf943c6-5146-4273-98dd-e958fd1e3abf
status: test
description: Detects all variations of obfuscated powershell IEX invocation code generated by Invoke-Obfuscation framework from the following code block
references:
    - https://github.com/danielbohannon/Invoke-Obfuscation/blob/f20e7f843edd0a3a7716736e9eddfa423395dd26/Out-ObfuscatedStringCommand.ps1#L873-L888
author: 'Daniel Bohannon (@Mandiant/@FireEye), oscd.community'
date: 2019-11-08
modified: 2026-03-16
tags:
    - attack.stealth
    - attack.t1027
    - attack.execution
    - attack.t1059.001
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        - CommandLine|re: '\$PSHome\[\s*\d{1,3}\s*\]\s*\+\s*\$PSHome\['
        - CommandLine|re: '\$ShellId\[\s*\d{1,3}\s*\]\s*\+\s*\$ShellId\['
        - CommandLine|re: '\$env:Public\[\s*\d{1,3}\s*\]\s*\+\s*\$env:Public\['
        - CommandLine|re: '\$env:ComSpec\[(?:\s*\d{1,3}\s*,){2}'
        - CommandLine|re: '\*mdr\*\W\s*\)\.Name'
        - CommandLine|re: '\$VerbosePreference\.ToString\('
        - CommandLine|re: '\[String\]\s*\$VerbosePreference'
    condition: selection
falsepositives:
    - Unknown
level: high

Stages and Predicates

Stage 0: condition

selection

Stage 1: selection

selection:
    - CommandLine|re: '\$PSHome\[\s*\d{1,3}\s*\]\s*\+\s*\$PSHome\['
    - CommandLine|re: '\$ShellId\[\s*\d{1,3}\s*\]\s*\+\s*\$ShellId\['
    - CommandLine|re: '\$env:Public\[\s*\d{1,3}\s*\]\s*\+\s*\$env:Public\['
    - CommandLine|re: '\$env:ComSpec\[(?:\s*\d{1,3}\s*,){2}'
    - CommandLine|re: '\*mdr\*\W\s*\)\.Name'
    - CommandLine|re: '\$VerbosePreference\.ToString\('
    - CommandLine|re: '\[String\]\s*\$VerbosePreference'

Indicators

These rows show field, operator, and value matches.

FieldKindValuesSearch
CommandLineregex_match
  • $PSHome[\s*\d{1,3}\s*]\s*+\s*$PSHome[
  • $ShellId[\s*\d{1,3}\s*]\s*+\s*$ShellId[
  • $VerbosePreference.ToString(
  • $env:ComSpec[(?:\s*\d{1,3}\s*,){2}
  • $env:Public[\s*\d{1,3}\s*]\s*+\s*$env:Public[
  • *mdr*\W\s*).Name
  • [String]\s*$VerbosePreference
field:"CommandLine" kind:regex_match