Potential PowerShell Command Line Obfuscation

Detects the PowerShell command lines with special characters

Detection logic

selection_img

- Image|endswith:
    - \powershell.exe
    - \pwsh.exe
- OriginalFileName:
    - PowerShell.EXE
    - pwsh.dll

selection_re

- CommandLine|re: \+.*\+.*\+.*\+.*\+.*\+.*\+.*\+.*\+.*\+.*\+.*\+.*\+.*\+
- CommandLine|re: \{.*\{.*\{.*\{.*\{.*\{.*\{.*\{.*\{.*\{
- CommandLine|re: \^.*\^.*\^.*\^.*\^
- CommandLine|re: "`.*`.*`.*`.*`"

filter_optional_amazonSSM

ParentImage: C:\Program Files\Amazon\SSM\ssm-document-worker.exe

filter_optional_defender_atp

CommandLine|contains:
  - new EventSource("Microsoft.Windows.Sense.Client.Management"
  - public static extern bool InstallELAMCertificateInfo(SafeFileHandle handle);

Condition

all of selection_* and not 1 of filter_optional_*

Raw YAML

title: Potential PowerShell Command Line Obfuscation
id: d7bcd677-645d-4691-a8d4-7a5602b780d1
status: test
description: Detects the PowerShell command lines with special characters
references:
    - https://speakerdeck.com/heirhabarov/hunting-for-powershell-abuse?slide=64
author: Teymur Kheirkhabarov (idea), Vasiliy Burov (rule), oscd.community, Tim Shelton (fp)
date: 2020-10-15
modified: 2024-04-15
tags:
    - attack.execution
    - attack.stealth
    - attack.t1027
    - attack.t1059.001
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        - Image|endswith:
              - '\powershell.exe'
              - '\pwsh.exe'
        - OriginalFileName:
              - 'PowerShell.EXE'
              - 'pwsh.dll'
    selection_re:
        # TODO: Optimize for PySIGMA
        - CommandLine|re: '\+.*\+.*\+.*\+.*\+.*\+.*\+.*\+.*\+.*\+.*\+.*\+.*\+.*\+'
        - CommandLine|re: '\{.*\{.*\{.*\{.*\{.*\{.*\{.*\{.*\{.*\{'
        - CommandLine|re: '\^.*\^.*\^.*\^.*\^'
        - CommandLine|re: '`.*`.*`.*`.*`'
    filter_optional_amazonSSM:
        ParentImage: C:\Program Files\Amazon\SSM\ssm-document-worker.exe
    filter_optional_defender_atp:
        CommandLine|contains:
            - 'new EventSource("Microsoft.Windows.Sense.Client.Management"'
            - 'public static extern bool InstallELAMCertificateInfo(SafeFileHandle handle);'
    condition: all of selection_* and not 1 of filter_optional_*
falsepositives:
    - Amazon SSM Document Worker
    - Windows Defender ATP
level: high