Suspicious FromBase64String Use On Gzip Archive - Ps Script (via ps_script)

title: Suspicious FromBase64String Use On Gzip Archive - Ps Script (via ps_script)
id: 7a724f37-7281-5785-ac33-e9977e08c14a
status: stable
description: This rule detects attempts of decoding a base64 Gzip archive in a PowerShell script. 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: 2026-02-16
tags:
    - attack.command-and-control
    - attack.t1132.001
logsource:
    product: windows
    category: ps_script
    definition: 'Requirements: Script Block Logging must be enabled'
detection:
    selection:
        ScriptBlockText|contains|all:
            - 'FromBase64String'
            - 'MemoryStream'
            - 'H4sI'
    condition: selection
falsepositives:
    - Unknown
level: medium