windows enabled community high v1.0.0

fsi

64-bit FSharp (F#) Interpreter included with Visual Studio and DotNet Core SDK. Located at: C:\Program Files\dotnet\sdk\<version>\FSharp\fsi.exe; C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\Common7\IDE\CommonExtensions\Microsoft\FSharp\fsi.exe.

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fsi
fsi

Sandbox: execFile · Timeout: 30s

Capabilities

security.defense-evasion.bypass

Contract

Outputs

process.output

Command execution output

Side effects: process_spawn

Workflow Edges

Produces

process.output

Resource Profile

ResourceValue
CPUlow
Memory16 MB
Networklow
Disk I/Olow

Examples

Execute F# code via script file (Execute payload with Microsoft signed binary to bypass WDAC policies)

fsi.exe {PATH:.fsscript}

Execute F# code via interactive command line (Execute payload with Microsoft signed binary to bypass WDAC policies)

fsi.exe

Detection

TypeRule / Indicator
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

Documentation

fsi

fsi is a Windows LOLBin. 64-bit FSharp (F#) Interpreter included with Visual Studio and DotNet Core SDK. Located at: C:\Program Files\dotnet\sdk<version>\FSharp\fsi.exe; C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\Common7\IDE\CommonExtensions\Microsoft\FSharp\fsi.exe.

References