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Detection rules › Sigma

Invoke-Obfuscation VAR+ Launcher - PowerShell

Status
test
Severity
high
Log source
category ps_script, product windows
Author
Jonathan Cheong, oscd.community
Source
github.com/SigmaHQ/sigma

Detects Obfuscated use of Environment Variables to execute PowerShell

MITRE ATT&CK coverage

TacticTechniques
Execution
Stealth

Telemetry coverage

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

Rule body

title: Invoke-Obfuscation VAR+ Launcher - PowerShell
id: 0adfbc14-0ed1-11eb-adc1-0242ac120002
status: test
description: Detects Obfuscated use of Environment Variables to execute PowerShell
references:
    - https://github.com/SigmaHQ/sigma/issues/1009  # (Task 24)
author: Jonathan Cheong, oscd.community
date: 2020-10-15
modified: 2024-04-05
tags:
    - attack.stealth
    - attack.t1027
    - attack.execution
    - attack.t1059.001
logsource:
    product: windows
    category: ps_script
    definition: 'Requirements: Script Block Logging must be enabled'
detection:
    selection_4104:
        ScriptBlockText|re: 'cmd.{0,5}(?:/c|/r)(?:\s|)"set\s[a-zA-Z]{3,6}.*(?:\{\d\}){1,}\\"\s+?-f(?:.*\)){1,}.*"'
    condition: selection_4104
falsepositives:
    - Unknown
level: high

Stages and Predicates

Stage 0: condition

selection_4104

Stage 1: selection_4104

selection_4104:
    ScriptBlockText|re: 'cmd.{0,5}(?:/c|/r)(?:\s|)"set\s[a-zA-Z]{3,6}.*(?:\{\d\}){1,}\\"\s+?-f(?:.*\)){1,}.*"'

Indicators

These rows show field, operator, and value matches.

FieldKindValuesSearch
ScriptBlockTextregex_match
  • cmd.{0,5}(?:/c|/r)(?:\s|)"set\s[a-zA-Z]{3,6}.*(?:{\d}){1,}\"\s+?-f(?:.*)){1,}.*"
field:"ScriptBlockText" kind:regex_match