PowerShell Obfuscation Through stdin via ScriptBlockText

Detects obfuscated PowerShell script blocks that use chained stdin/environment/input patterns.

FreeUnreviewedSigmahighv1

powershell-obfuscation-through-stdin-via-scriptblocktext-86b896ba

title: PowerShell Obfuscation Through stdin via ScriptBlockText
id: 9cc577c9-de1c-4b41-a05f-2a3c9d1b2c95
status: test
description: This rule flags PowerShell script blocks where the ScriptBlockText contains patterns consistent with chained commands that manipulate environment/input and invoke activity using stdin. Attackers often use obfuscation and stdin-driven input to hinder analysis and execute logic indirectly. The detection relies on ScriptBlockText content from PowerShell script block logging, matching a case-insensitive regular expression over the script block text.
references:
  - https://github.com/SigmaHQ/sigma/issues/1009
  - https://github.com/SigmaHQ/sigma/blob/master/rules/windows/powershell/powershell_script/posh_ps_invoke_obfuscation_via_stdin.yml
author: Nikita Nazarov, oscd.community, Huntrule Team
date: 2020-10-12
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: (?i)(set).*&&\s?set.*(environment|invoke|\$\{?input).*&&.*"
  condition: selection_4104
falsepositives:
  - Unknown
level: high
license: DRL-1.1
related:
  - id: 86b896ba-ffa1-4fea-83e3-ee28a4c915c7
    type: derived

What it detects

This rule flags PowerShell script blocks where the ScriptBlockText contains patterns consistent with chained commands that manipulate environment/input and invoke activity using stdin. Attackers often use obfuscation and stdin-driven input to hinder analysis and execute logic indirectly. The detection relies on ScriptBlockText content from PowerShell script block logging, matching a case-insensitive regular expression over the script block text.

Known false positives

Unknown

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.