Base64 Encoded PowerShell Execution

SIGMA detection rule by Momen Mahmoud

Detects PowerShell (or pwsh) processes using the -EncodedCommand (or -enc/-e) flag to execute Base64-encoded commands, which may indicate malicious activity.

title: Base64 Encoded PowerShell Execution 
id: a558c283-86d4-4ccc-849e-2096099001ec
status: experimental
description: |
  Detects PowerShell (or pwsh) processes using the -EncodedCommand (or -enc/-e) flag to execute Base64-encoded commands, which may indicate malicious activity.
references:
  - https://kqlquery.com/posts/hunting-encoded-powershell/
  - https://github.com/Bert-JanP/Hunting-Queries-Detection-Rules/blob/main/Threat%20Hunting%20Cases/Suspicious%20Encoded%20Powershell.md
author: Momen Mahmoud
date: 2025-02-12
tags:
  - attack.execution
  - attack.t1059.001
logsource:
  category: process_creation
  product: windows
detection:
  selection:
    Image|endswith:
      - '\powershell.exe'
      - '\pwsh.exe'
    CommandLine|re:
      - '(?i)(-EncodedCommand|-enc|-e)\s+[A-Za-z0-9+/]+={0,2}'
  condition: selection
falsepositives:
  - Legitimate administrative scripts that use encoded commands
level: medium

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

dd516d10-f495-4435-bff7-cdf72e0857d2

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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

[[ reason ]]

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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.

[[ reason ]]

What do these messages mean?

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

[[ currentRule.title ]]

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