.. /csi.exe

Star

Paths:

• c:\Program Files (x86)\Microsoft Visual Studio\2017\Community\MSBuild\15.0\Bin\Roslyn\csi.exe
• c:\Program Files (x86)\Microsoft Web Tools\Packages\Microsoft.Net.Compilers.X.Y.Z\tools\csi.exe

Resources:

• https://twitter.com/subTee/status/781208810723549188
• https://enigma0x3.net/2016/11/17/bypassing-application-whitelisting-by-using-dnx-exe/

Acknowledgements:

• Casey Smith (@subtee)

Detections:

• Sigma: https://github.com/SigmaHQ/sigma/blob/c04bef2fbbe8beff6c7620d5d7ea6872dbe7acba/rules/windows/process_creation/proc_creation_win_csi_execution.yml
• Sigma: https://github.com/SigmaHQ/sigma/blob/683b63f8184b93c9564c4310d10c571cbe367e1e/rules/windows/process_creation/proc_creation_win_csi_use_of_csharp_console.yml
• 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

Execute

1. Use csi.exe to run unsigned C# code.

   csi.exe file

   Use case

   Local execution of unsigned C# code.

   Privileges required

   User

   Operating systems

   Windows

   ATT&CK® technique

   T1127