COMRunner

A simple COM server which provides a component to run shellcode. Also includes a Windows JScript file to load the COM server and create the object with registration-free activation. This PoC COM server provides an object with a method that takes in base64 encoded shellcode and a method to run the shellcode.

For a more exhaustive background, see the blog post here: https://adapt-and-attack.com/2020/05/12/building-a-com-server-for-initial-execution/

Contents

COM Client (JScript) to activate the object and run shellcode

• script.js

COM Class definition and C++ implementation:

• COMRunner\object.cpp
• COMRunner\object.h

IDL Object Definition:

• COMRunner\TestClass.idl

Generated files from midl.exe compilation:

• COMRunner\TestClass.h
• COMRunner\TestClass.tlb
• COMRunner\TestClass_i.c
• COMRunner\TestClass_p.c
• COMRunner\dlldata.c

Resource Embedding:

• COMRunner\resource.rc specifying resources to embed
• COMRunner\resource.res generated file from rc COMRunner\resource.rc, file is pulled in to embed TLB at compile time

Other:

• COMRunner\dllmain.cpp has typical dllmain functions and DllGetClassObject implementation
• COMRunner\Helpers.h includes some helper functions
• COMRunner\Source.def defines exported functions

Changing the Object

As described later in the blog post, which is probably the best way to understand if this is new to you, the COM object's structure is identified in the TestClass.idl file. If you want to add another method or take an additional input, you will want to follow these general steps. These may not be the only way, so feel free to stray away as well.

1. Update the TestClass.idl with your desired changes
2. Regenerate files with midl.exe TestClass.idl
3. The new TLB needs to be embedded. Run rc resource.rc to generated a new resource.res
4. Update object.h class to ensure it implements your new interface defined in TestClass.idl
5. Update object.cpp to change/add/remove your object's method's code

Thanks

• Much thanks to @subTee for the research this was built on: https://www.youtube.com/watch?v=BIJ2L_rM9Gc
• Inside COM by Dale Rogerson
• For ClassFactory code: https://www.codeguru.com/cpp/com-tech/activex/tutorials/article.php/c5567/Step-by-Step-COM-Tutorial.htm