Can You Run an EXE from a Memory Buffer Using CreateProcess?

Running an EXE from a Memory Buffer Using CreateProcess

The CreateProcess function is commonly used to launch an executable (EXE) stored in a file. However, is it possible to run an EXE directly from a memory buffer without writing it to a file? This question arises in scenarios such as game patching, where you may need to update a wrapped EXE without disabling DRM.

Solution:

Yes, it's possible to run an EXE from a memory buffer using CreateProcess with the following steps:

1. Suspend Process Creation: Call CreateProcess with the CREATE_SUSPENDED flag to suspend the process. This gives time to modify the process memory.
2. Get Process Context: Retrieve the suspended thread's context using GetThreadContext. The EBX register contains a pointer to the Process Environment Block (PEB) structure.
3. Determine Base Address: Obtain the base address of the process from [EBX 8] in the PEB structure.
4. Copy In-Memory EXE: Write the in-memory EXE into the memory space of the suspended process using WriteProcessMemory if the base addresses and image sizes match.
5. Adjust for Mismatched Conditions: In case of mismatched conditions, unmap the original image using ZwUnmapViewOfSection, allocate memory using VirtualAllocEx, write the in-memory EXE, and patch the PEB->ImageBaseAddress.
6. Set Entry Point: Rewrite the EntryPoint address in the thread context with the entry point of the in-memory EXE.
7. Resume Process: Finally, resume the suspended process using ResumeThread.

By following these steps, you can effectively run an EXE from a memory buffer without having to write it to a file, fulfilling the requirement to distribute patches without disrupting the DRM wrapper.

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