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Detection rules › Sigma

Potential PowerShell Obfuscation Using Character Join

Status
test
Severity
low
Log source
category ps_script, product windows
Author
Nasreddine Bencherchali (Nextron Systems)
Source
github.com/SigmaHQ/sigma

Detects specific techniques often seen used inside of PowerShell scripts to obfscuate Alias creation

MITRE ATT&CK coverage

TacticTechniques
Execution
Stealth

Telemetry coverage

ProviderRecord / event type
PowerShellEvent ID 4104: Creating Scriptblock text (MessageNumber of MessageTotal).

Rule body

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

Stages and Predicates

Stage 0: condition

selection

Stage 1: selection

selection:
    ScriptBlockText|contains|all:
        - '-Alias'
        - ' -Value (-join('

Indicators

These rows show field, operator, and value matches.

FieldKindValuesSearch
ScriptBlockTextmatch
  • -Value (-join(
  • -Alias
field:"ScriptBlockText" kind:match