Suspicious FromBase64String Use On Gzip Archive - Process Creation (via process_creation)

title: Suspicious FromBase64String Use On Gzip Archive - Process Creation (via process_creation)
id: 3a0759fd-b92e-521f-a5c1-0fbc34584117
status: stable
description: This rule detects attempts of decoding a base64 Gzip archive via PowerShell. This method is frequently used as a method to load hostile content into memory afterward.
references:
    - https://attack.mitre.org/techniques/T1132/001/
    - https://speakerdeck.com/heirhabarov/hunting-for-powershell-abuse?slide=43
author: Huntrule Team
date: 2026-01-30
tags:
    - attack.command-and-control
    - attack.t1132.001
logsource:
    product: windows
    category: process_creation
detection:
    selection:
        CommandLine|contains|all:
            - 'FromBase64String'
            - 'MemoryStream'
            - 'H4sI'
    condition: selection
falsepositives:
    - Unknown
level: medium