Can CreateProcess Execute an EXE Directly from Memory Without Saving It to a File?

CreateProcess from Memory Buffer

Question:

Can one invoke CreateProcess on the contents of an EXE stored in a memory buffer, without writing it to a file first?

Background:

In an attempt to bypass DRM delays in patching game crashes, a method is sought to decrypt and launch a real EXE from within an external EXE.

Answer:

CreateProcess can indeed be invoked on a memory buffer containing an EXE, allowing for its execution without prior file writing. The steps involve:

1. Suspending the process using CreateProcess with the CREATE_SUSPENDED flag.
2. Retrieving the thread context using GetThreadContext, with the PEB's ImageBaseAddress stored at [EBX 8].
3. Comparing the base addresses and image sizes of the suspended process and in-memory EXE.
4. Writing the in-memory EXE into the suspended process's memory using WriteProcessMemory if conditions allow.
5. Unmapping the original image, allocating memory in the suspended process, and writing the in-memory EXE if conditions do not allow.
6. Patching the base address and entry point in the thread context.
7. Resuming the suspended process using ResumeThread.

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