Invoke-Obfuscation Obfuscated IEX Invocation - System — Sigma Rule

Rule metadata and linked tags

Author: Daniel Bohannon (@Mandiant/@FireEye), oscd.community. Source status: test; severity: high. Source dates: 2019-11-08 / 2022-11-27.

{
  "product": "windows",
  "service": "system"
}

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: 6b13bb822d87decfe759380fc4d73a0864fa118e11eaf9ef5e8203c9f7f8751e

Detection logic

Original source YAML. Source-tag agreement is not proof of complete semantic coverage. This rule has not been compiled for a SIEM backend or validated against live telemetry here.

title: Invoke-Obfuscation Obfuscated IEX Invocation - System
id: 51aa9387-1c53-4153-91cc-d73c59ae1ca9
status: test
description: Detects all variations of obfuscated powershell IEX invocation code generated by Invoke-Obfuscation framework from the code block linked in the references
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: 2022-11-27
tags:
    - attack.stealth
    - attack.t1027
logsource:
    product: windows
    service: system
detection:
    selection_eid:
        EventID: 7045
    selection_imagepath:
        - ImagePath|re: '\$PSHome\[\s*\d{1,3}\s*\]\s*\+\s*\$PSHome\['
        - ImagePath|re: '\$ShellId\[\s*\d{1,3}\s*\]\s*\+\s*\$ShellId\['
        - ImagePath|re: '\$env:Public\[\s*\d{1,3}\s*\]\s*\+\s*\$env:Public\['
        - ImagePath|re: '\$env:ComSpec\[(\s*\d{1,3}\s*,){2}'
        - ImagePath|re: '\\*mdr\*\W\s*\)\.Name'
        - ImagePath|re: '\$VerbosePreference\.ToString\('
        - ImagePath|re: '\String\]\s*\$VerbosePreference'
    condition: all of selection_*
falsepositives:
    - Unknown
level: high

Original YAML and metadata in JSON

False positives

• Unknown

Source references

• https://github.com/danielbohannon/Invoke-Obfuscation/blob/f20e7f843edd0a3a7716736e9eddfa423395dd26/Out-ObfuscatedStringCommand.ps1#L873-L888