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Detection rules › Sigma

Potential CommandLine Obfuscation Using Unicode Characters From Suspicious Image

Status
test
Severity
high
Log source
product windows, category process_creation
Author
frack113, Florian Roth (Nextron Systems), Josh Nickels
Source
github.com/SigmaHQ/sigma

Detects potential commandline obfuscation using unicode characters. Adversaries may attempt to make an executable or file difficult to discover or analyze by encrypting, encoding, or otherwise obfuscating its contents on the system or in transit.

MITRE ATT&CK coverage

TacticTechniques
StealthT1027 Obfuscated Files or Information

Event coverage

ProviderEventTitle
SysmonEvent ID 1Process creation

Rule body yaml

title: Potential CommandLine Obfuscation Using Unicode Characters From Suspicious Image
id: 584bca0f-3608-4402-80fd-4075ff6072e3
related:
    - id: e0552b19-5a83-4222-b141-b36184bb8d79
      type: similar
    - id: ad691d92-15f2-4181-9aa4-723c74f9ddc3 # RTLO
      type: similar
    - id: 2c0d2d7b-30d6-4d14-9751-7b9113042ab9
      type: obsolete
status: test
description: |
    Detects potential commandline obfuscation using unicode characters.
    Adversaries may attempt to make an executable or file difficult to discover or analyze by encrypting, encoding, or otherwise obfuscating its contents on the system or in transit.
references:
    - https://www.wietzebeukema.nl/blog/windows-command-line-obfuscation
    - https://github.com/redcanaryco/atomic-red-team/blob/f339e7da7d05f6057fdfcdd3742bfcf365fee2a9/atomics/T1027/T1027.md#atomic-test-6---dlp-evasion-via-sensitive-data-in-vba-macro-over-http
author: frack113, Florian Roth (Nextron Systems), Josh Nickels
date: 2024-09-02
modified: 2025-05-30
tags:
    - attack.stealth
    - attack.t1027
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        Image|endswith:
            - '\cmd.exe'
            - '\cscript.exe'
            - '\powershell.exe'
            - '\powershell_ise.exe'
            - '\pwsh.exe'
            - '\wscript.exe'
        OriginalFileName:
            - 'Cmd.EXE'
            - 'cscript.exe'
            - 'PowerShell.EXE'
            - 'PowerShell_ISE.EXE'
            - 'pwsh.dll'
            - 'wscript.exe'
    selection_special_chars:
        CommandLine|contains:
            # spacing modifier letters that get auto-replaced
            - 'ˣ' # 0x02E3
            - '˪' # 0x02EA
            - 'ˢ' # 0x02E2
            # Forward slash alternatives
            - '∕' # 0x22FF
            - '⁄' # 0x206F
            # Hyphen alternatives
            - '―' # 0x2015
            - '—' # 0x2014
            # Whitespace that don't work as path separator
            - ' ' # 0x00A0
            # Other
            - '¯'
            - '®'
            - '¶'
            # Unicode whitespace characters
            - '⠀' # Braille Pattern Blank (Unicode: U+2800)
    condition: all of selection_*
falsepositives:
    - Unknown
level: high

Stages and Predicates

Stage 0: condition

all of selection_*

Stage 1: selection_img

selection_img:
    Image|endswith:
        - '\cmd.exe'
        - '\cscript.exe'
        - '\powershell.exe'
        - '\powershell_ise.exe'
        - '\pwsh.exe'
        - '\wscript.exe'
    OriginalFileName:
        - 'Cmd.EXE'
        - 'cscript.exe'
        - 'PowerShell.EXE'
        - 'PowerShell_ISE.EXE'
        - 'pwsh.dll'
        - 'wscript.exe'

Stage 2: selection_special_chars

selection_special_chars:
    CommandLine|contains:
        - 'ˣ'
        - '˪'
        - 'ˢ'
        - '∕'
        - '⁄'
        - '―'
        - '—'
        - ' '
        - '¯'
        - '®'
        - '¶'
        - '⠀'

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

FieldKindValues
CommandLinematch
  •   corpus 2 (sigma 2)
  • ® corpus 2 (sigma 2)
  • ¯ corpus 2 (sigma 2)
  • corpus 2 (sigma 2)
  • ˢ corpus 2 (sigma 2)
  • ˣ corpus 2 (sigma 2)
  • ˪ corpus 2 (sigma 2)
  • — corpus 2 (sigma 2)
  • ― corpus 2 (sigma 2)
  • ⁄ corpus 2 (sigma 2)
  • ∕ corpus 2 (sigma 2)
  • ⠀
Imageends_with
  • \cmd.exe corpus 130 (sigma 130)
  • \cscript.exe corpus 73 (sigma 73)
  • \powershell.exe corpus 182 (sigma 182)
  • \powershell_ise.exe corpus 41 (sigma 41)
  • \pwsh.exe corpus 168 (sigma 168)
  • \wscript.exe corpus 75 (sigma 75)
OriginalFileNameeq
  • Cmd.EXE corpus 65 (sigma 43, splunk 17, elastic 5)
  • PowerShell.EXE corpus 120 (sigma 84, splunk 30, elastic 6)
  • PowerShell_ISE.EXE corpus 51 (splunk 30, sigma 18, elastic 3)
  • cscript.exe corpus 19 (sigma 17, elastic 2)
  • pwsh.dll corpus 112 (sigma 79, splunk 30, elastic 3)
  • wscript.exe corpus 20 (sigma 17, elastic 3)