Fsi.exe
64-bit FSharp (F#) Interpreter included with Visual Studio and DotNet Core SDK.
Paths
C:\Program Files\dotnet\sdk\<version>\FSharp\fsi.exeC:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\Common7\IDE\CommonExtensions\Microsoft\FSharp\fsi.exe
Commands
AWL Bypass
Execute F# code via script file
Use case: Execute payload with Microsoft signed binary to bypass WDAC policies
Privileges: User
fsi.exe {PATH:.fsscript}AWL Bypass
Execute F# code via interactive command line
Use case: Execute payload with Microsoft signed binary to bypass WDAC policies
Privileges: User
fsi.exeDetection
- 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