LOL · OtherMSBinary

Fsi.exe

2 techniquesWindowsLOLBASGPL-3.0

AWL Bypass

AWL / Policy BypassWindows

Execute F# code via script file

Use Execute payload with Microsoft signed binary to bypass WDAC policies

fsi.exe {PATH:.fsscript}

Evidence: Upstream reference
Environment: Local host
Context: user
Native: AWL Bypass
MITRE: T1059
Detection: Elastic: github.com/elastic/detection-rules/blob/414d32027632a49fb239abb8fbbb55d3fa8dd861/rules/windows/defense_evasion_unusual_process_network_connection.toml
Elastic: github.com/elastic/detection-rules/blob/414d32027632a49fb239abb8fbbb55d3fa8dd861/rules/windows/defense_evasion_network_connection_from_windows_binary.toml
BlockRule: 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: github.com/SigmaHQ/sigma/blob/6b34764215b0e97e32cbc4c6325fc933d2695c3a/rules/windows/process_creation/proc_creation_win_lolbin_fsharp_interpreters.yml
Refs: twitter.com/NickTyrer/status/904273264385589248
bohops.com/2020/11/02/exploring-the-wdac-microsoft-recommended-block-rules-part-ii-wfc-fsi/
lolbas-project.github.io/lolbas/OtherMSBinaries/Fsi/

AWL / Policy BypassWindows

Execute F# code via interactive command line

Use Execute payload with Microsoft signed binary to bypass WDAC policies

fsi.exe

Evidence: Upstream reference
Environment: Local host
Context: user
Native: AWL Bypass
MITRE: T1059
Detection: Elastic: github.com/elastic/detection-rules/blob/414d32027632a49fb239abb8fbbb55d3fa8dd861/rules/windows/defense_evasion_unusual_process_network_connection.toml
Elastic: github.com/elastic/detection-rules/blob/414d32027632a49fb239abb8fbbb55d3fa8dd861/rules/windows/defense_evasion_network_connection_from_windows_binary.toml
BlockRule: 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: github.com/SigmaHQ/sigma/blob/6b34764215b0e97e32cbc4c6325fc933d2695c3a/rules/windows/process_creation/proc_creation_win_lolbin_fsharp_interpreters.yml
Refs: twitter.com/NickTyrer/status/904273264385589248
bohops.com/2020/11/02/exploring-the-wdac-microsoft-recommended-block-rules-part-ii-wfc-fsi/
lolbas-project.github.io/lolbas/OtherMSBinaries/Fsi/