Potential PowerShell Obfuscation Using Character Join — Sigma Rule

Rule metadata and linked tags

Author: Nasreddine Bencherchali (Nextron Systems). Source status: test; severity: low. Source dates: 2023-01-09 / not supplied.

{
  "product": "windows",
  "category": "ps_script",
  "definition": "Requirements: Script Block Logging must be enabled"
}

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: e731d5ced65dc5f0c49785c98de883c65a07791ed776c4c4b7959a30d1d7bc76

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: Potential PowerShell Obfuscation Using Character Join
id: e8314f79-564d-4f79-bc13-fbc0bf2660d8
related:
    - id: 96cd126d-f970-49c4-848a-da3a09f55c55
      type: derived
status: test
description: Detects specific techniques often seen used inside of PowerShell scripts to obfscuate Alias creation
references:
    - Internal Research
author: Nasreddine Bencherchali (Nextron Systems)
date: 2023-01-09
tags:
    - attack.execution
    - attack.stealth
    - attack.t1027
    - attack.t1059.001
logsource:
    product: windows
    category: ps_script
    definition: 'Requirements: Script Block Logging must be enabled'
detection:
    selection:
        # Example:
        #   Set-Alias -Name Y -Value (-join("Ne","w-O","bje","ct"))
        #   Set-Alias -Name X -Value (-join("Inv","oke","-","Exp","ression"))
        ScriptBlockText|contains|all:
            - '-Alias' # For both "New-Alias" and "Set-Alias"
            - ' -Value (-join('
    condition: selection
falsepositives:
    - Unknown
level: low

Original YAML and metadata in JSON

False positives

• Unknown

Source references

• Internal Research (source note; no public URL supplied)