PowerShell Base64 Encoded FromBase64String Cmdlet

Description

Detects usage of a base64 encoded "FromBase64String" cmdlet in a process command line

Query · sigma

selection:
- CommandLine|base64offset|contains: ::FromBase64String
- CommandLine|contains:
  - OgA6AEYAcgBvAG0AQgBhAHMAZQA2ADQAUwB0AHIAaQBuAGcA
  - oAOgBGAHIAbwBtAEIAYQBzAGUANgA0AFMAdAByAGkAbgBnA
  - 6ADoARgByAG8AbQBCAGEAcwBlADYANABTAHQAcgBpAG4AZw
condition: selection

Known false positives

  • Unknown
Raw source PowerShell Base64 Encoded FromBase64String Cmdlet · Sigma
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Published by SigmaHQ/sigma ↗, licensed under Detection Rule License 1.1 ↗. Reproduced here unmodified. 
title: PowerShell Base64 Encoded FromBase64String Cmdlet
id: fdb62a13-9a81-4e5c-a38f-ea93a16f6d7c
status: test
description: Detects usage of a base64 encoded "FromBase64String" cmdlet in a process command line
references:
    - Internal Research
author: Florian Roth (Nextron Systems)
date: 2019-08-24
modified: 2023-04-06
tags:
    - attack.stealth
    - attack.t1140
    - attack.execution
    - attack.t1059.001
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        - CommandLine|base64offset|contains: '::FromBase64String'
        # UTF-16 LE
        - CommandLine|contains:
              - 'OgA6AEYAcgBvAG0AQgBhAHMAZQA2ADQAUwB0AHIAaQBuAGcA'
              - 'oAOgBGAHIAbwBtAEIAYQBzAGUANgA0AFMAdAByAGkAbgBnA'
              - '6ADoARgByAG8AbQBCAGEAcwBlADYANABTAHQAcgBpAG4AZw'
    condition: selection
falsepositives:
    - Unknown
level: high

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