Obfuscation and Escape Characters - Powershell

SIGMA detection rule by RedCanary, Sigma formatting by Micah Babinski · GPL-3.0

This analytic looks for the execution of a process that seems to be powershell.exe along with a corresponding command line containing the term base64. Base64 encoding isn’t inherently suspicious, but it’s worth looking out for in a lot of environments, and the following pseudo-detection logic can help detect a wide variety of malicious activity. Part of the RedCanary 2024 Threat Detection Report.

title: Obfuscation and Escape Characters - Powershell
id: b47fccc1-8407-4fca-ae31-ef49d0ae0410
status: experimental
description: |
    This analytic looks for the execution of a process that seems to be 
    powershell.exe along with a corresponding command line containing the 
    term base64. Base64 encoding isn’t inherently suspicious, but it’s worth 
    looking out for in a lot of environments, and the following pseudo-detection 
    logic can help detect a wide variety of malicious activity. Part of the 
    RedCanary 2024 Threat Detection Report.
references:
    - https://redcanary.com/threat-detection-report/techniques/powershell/
author: RedCanary, Sigma formatting by Micah Babinski
date: 2024/03/21
tags:
    - attack.execution
    - attack.t1059
    - attack.t1059.001
    - attack.defense_evasion
    - attack.t1027
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith: '\powershell.exe'
        # regex below looks for eight or more total instances of the suspicious characters
        CommandLine|re: '^([^^=%![(; ]*[\^=%![(; ]){8,}[^^=%![(; ]*$'
    condition: selection
falsepositives:
    - Unknown
level: low

[[ currentRule.title && currentRule.title.length > 60 ? currentRule.title.slice(0, 60) + '…' : currentRule.title ]]

84cc3187-961a-4c03-a5f3-5840a170cba4

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Executable code, not a declarative rule

This submission is arbitrary [[ currentRule.format ? currentRule.format.toUpperCase() : '' ]] code, not a declarative detection rule — review it as you would any script before running it, and note that it cannot be safely aggregated or auto-executed alongside YARA/Sigma/Suricata/CRS rules.

Rejected pattern present

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Format & documentation suggestions

Not a security issue — this rule is valid and was accepted as-is. These are optional fields/conventions its own format recommends, mainly affecting its quality score and how well it documents itself for other reviewers.

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What do these messages mean?

[[ currentRule.title && currentRule.title.length > 60 ? currentRule.title.slice(0, 60) + '…' : currentRule.title ]]

[[ currentRule.title ]]

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