Suspicious Use of FSharp Interpreters (via process_creation)

title: Suspicious Use of FSharp Interpreters (via process_creation)
id: 92cea561-a1b1-5c5e-b7bb-11dc92bd1cc1
status: stable
description: This rule detects the execution of FSharp Interpreters "FsiAnyCpu.exe" and "FSi.exe" Both can be used for AWL bypass and to execute F# code via scripts or inline.
references:
    - https://attack.mitre.org/techniques/T1059/
    - https://learn.microsoft.com/en-us/windows/security/application-security/application-control/windows-defender-application-control/design/applications-that-can-bypass-wdac
    - https://bohops.com/2020/11/02/exploring-the-wdac-microsoft-recommended-block-rules-part-ii-wfc-fsi/
    - https://lolbas-project.github.io/lolbas/OtherMSBinaries/FsiAnyCpu/
    - https://lolbas-project.github.io/lolbas/OtherMSBinaries/Fsi/
author: Huntrule Team
date: 2026-07-07
tags:
    - attack.execution
    - attack.t1059
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        - Image|endswith:
              - '\fsi.exe'
              - '\fsianycpu.exe'
        - OriginalFileName:
              - 'fsi.exe'
              - 'fsianycpu.exe'
    condition: selection
falsepositives:
    - Unknown
level: medium