Possible AMSI Bypass Script Via NULL Bits (via ps_script)

title: Possible AMSI Bypass Script Via NULL Bits (via ps_script)
id: 418ccb37-f228-5453-8c07-5e44679a8c60
status: stable
description: This rule detects use of special strings/null bits to potentially bypass AMSI functionalities
references:
    - https://attack.mitre.org/techniques/T1685/
    - https://github.com/r00t-3xp10it/hacking-material-books/blob/43cb1e1932c16ff1f58b755bc9ab6b096046853f/obfuscation/simple_obfuscation.md#amsi-bypass-using-null-bits-satoshi
author: Huntrule Team
date: 2026-06-09
tags:
    - attack.defense-impairment
    - attack.t1685
logsource:
    product: windows
    category: ps_script
    definition: 'Requirements: Script Block Logging must be enabled'
detection:
    selection:
        ScriptBlockText|contains:
            - "if(0){{{0}}}' -f $(0 -as [char]) +"
            - "#<NULL>"
    condition: selection
falsepositives:
    - Unknown
level: medium