Procmon (process monitor) is a troubleshooting tool from Windows Sysinternals that display the file and registry that applications access in real-time. To view the file creation and all others file modification, let’s use “procmon”. Iex is Invoke-Expression and that is used to run a command or expression on a local system.Ī static function is a member function of a class that can be called even when an object of the class is not initialized. :: is used to call a static member of the class. Since we are using inline source code, TypeDefinition parameter specify that the code source is stored in the $code variable. Let's create a PowerShell script calling that csc.exe with the cmdlet Add-Type to compile dynamically this C# code. This C# code will simply display "Hello World !". After executing the cmdlet Add-Type, PowerShell will run csc.exe. In this part, we are going to create a PowerShell script with Add-Type cmlet to compile a C# code. POC: Analyzing PowerShell calling csc.exe Since, it is compiling the code when the program has been executed, it means that we can run malicious C# code through PowerShell. During execution, the program may be compiled into native code to improve its performance. However, by compiling C# with PowerShell, the Code Integrity checks are not performed on any code that compiles C# dynamically with csc.exe.ĭelaying compilation of a program, it can be done at program load, or on demand as code is executed. The Code Integrity is based on the virtualization and when the system is booting, Hyper-V Code Integrity verifies that every script and driver running at boot on the system are signed. ![]() Therefore, it become harder to run a malicious code because it might be blocked by Device Guard. Device Guard uses a technology called " Code Integrity” which will verify the integrity of the Windows kernel before running any script. It allows to lock any device to only run signed and allowed applications and scripts. By compiling dynamically C# with PowerShell, it has been demontrated that it can evade detection from Device Guard since Code Integrity is not performed.ĭevice Guard is a functionality developed by Microsoft, available only on Windows 10 Enterprise. NET Core object, so C# Object can be created as well with that cmdlet. With that cmdlet, it is possible to instantiate. NET Core class in the PowerShell session. A temporary file XXXX.cmdline is created in AppData\local\temp and this file will be passed as argument to the C# compiler csc.exe to create XXXX.0.cs in AppData\local\temp. In PowerShell, when the cmdlet “ Add-type” is executed, it will run the csc.exe to compile the C# code into a machine language.
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