Potential Encoded PowerShell Patterns In CommandLine

title: Potential Encoded PowerShell Patterns In CommandLine
id: cdf05894-89e7-4ead-b2b0-0a5f97a90f2f
related:
    - id: 5b572dcf-254b-425c-a8c5-d9af6bea35a6
      type: similar
status: test
description: Detects specific combinations of encoding methods in PowerShell via the commandline
references:
    - https://speakerdeck.com/heirhabarov/hunting-for-powershell-abuse?slide=65
author: Teymur Kheirkhabarov (idea), Vasiliy Burov (rule), oscd.community, Tim Shelton
date: 2020-10-11
modified: 2023-01-26
tags:
    - attack.defense-evasion
    - attack.t1027
    - attack.execution
    - attack.t1059.001
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        - Image|endswith:
              - '\powershell.exe'
              - '\pwsh.exe'
        - OriginalFileName:
              - 'PowerShell.EXE'
              - 'pwsh.dll'
    selection_to_1:
        CommandLine|contains:
            - 'ToInt'
            - 'ToDecimal'
            - 'ToByte'
            - 'ToUint'
            - 'ToSingle'
            - 'ToSByte'
    selection_to_2:
        CommandLine|contains:
            - 'ToChar'
            - 'ToString'
            - 'String'
    selection_gen_1:
        CommandLine|contains|all:
            - 'char'
            - 'join'
    selection_gen_2:
        CommandLine|contains|all:
            - 'split'
            - 'join'
    condition: selection_img and (all of selection_to_* or 1 of selection_gen_*)
falsepositives:
    - Unknown
level: low