.. /Csc.exe
Star

Binary file used by .NET Framework to compile C# code

Paths:

C:\Windows\Microsoft.NET\Framework\v4.0.30319\Csc.exe
C:\Windows\Microsoft.NET\Framework64\v4.0.30319\Csc.exe
C:\Windows\Microsoft.NET\Framework\v3.5\csc.exe
C:\Windows\Microsoft.NET\Framework64\v3.5\csc.exe
C:\Windows\Microsoft.NET\Framework\v2.0.50727\csc.exe
C:\Windows\Microsoft.NET\Framework64\v2.0.50727\csc.exe

Resources:

https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/compiler-options/

Detections:

Sigma: https://github.com/SigmaHQ/sigma/blob/62d4fd26b05f4d81973e7c8e80d7c1a0c6a29d0e/rules/windows/process_creation/proc_creation_win_csc_susp_parent.yml
Sigma: https://github.com/SigmaHQ/sigma/blob/62d4fd26b05f4d81973e7c8e80d7c1a0c6a29d0e/rules/windows/process_creation/proc_creation_win_csc_susp_folder.yml
Elastic: https://github.com/elastic/detection-rules/blob/61afb1c1c0c3f50637b1bb194f3e6fb09f476e50/rules/windows/defense_evasion_dotnet_compiler_parent_process.toml
Elastic: https://github.com/elastic/detection-rules/blob/82ec6ac1eeb62a1383792719a1943b551264ed16/rules/windows/defense_evasion_execution_msbuild_started_unusal_process.toml
IOC: Csc.exe should normally not run as System account unless it is used for development.

Compile

Use csc.exe to compile C# code, targeting the .NET Framework, stored in File.cs and output the compiled version to Output.exe.
```
csc.exe -out:Output.exe File.cs
```
Use case
Compile attacker code on system. Bypass defensive counter measures.

Privileges required
User

Operating systems
Windows vista, Windows 7, Windows 8, Windows 8.1, Windows 10, Windows 11

ATT&CK® technique
T1127
Use csc.exe to compile C# code, targeting the .NET Framework, stored in File.cs and output the compiled version to a DLL file.
```
csc -target:library File.cs
```
Use case
Compile attacker code on system. Bypass defensive counter measures.

Privileges required
User

Operating systems
Windows vista, Windows 7, Windows 8, Windows 8.1, Windows 10, Windows 11

ATT&CK® technique
T1127