detection.wiki

Detection rules › Sigma

Invoke-Obfuscation VAR+ Launcher - PowerShell

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

Detects Obfuscated use of Environment Variables to execute PowerShell

MITRE ATT&CK coverage

TacticTechniques
ExecutionT1059.001 Command and Scripting Interpreter: PowerShell
StealthT1027 Obfuscated Files or Information

Event coverage

ProviderEventTitle
PowerShellEvent ID 4104Creating Scriptblock text (MessageNumber of MessageTotal).

Rule body yaml

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

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