64-bit FSharp (F#) Interpreter included with Visual Studio and DotNet Core SDK.
fsi.exe c:\path\to\test.fsscript
Execute F# code via script file
Execute payload with Microsoft signed binary to bypass WDAC policies
C:\Program Files\dotnet\sdk\[sdk version]\FSharp\fsi.exe, C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\Common7\IDE\CommonExtensions\Microsoft\FSharp\fsi.exe
Elastic: https://github.com/elastic/detection-rules/blob/414d32027632a49fb239abb8fbbb55d3fa8dd861/rules/windows/defense_evasion_unusual_process_network_connection.toml, Elastic: https://github.com/elastic/detection-rules/blob/414d32027632a49fb239abb8fbbb55d3fa8dd861/rules/windows/defense_evasion_network_connection_from_windows_binary.toml, BlockRule: https://docs.microsoft.com/en-us/windows/security/threat-protection/windows-defender-application-control/microsoft-recommended-block-rules, IOC: Fsi.exe execution may be suspicious on non-developer machines, Sigma: https://github.com/SigmaHQ/sigma/blob/6b34764215b0e97e32cbc4c6325fc933d2695c3a/rules/windows/process_creation/proc_creation_win_lolbin_fsharp_interpreters.yml
Nick Tyrer (@NickTyrer), Jimmy (@bohops)