How to Launch an EXE from Memory Buffer Without Writing to File?

Loading an EXE from Memory Buffer without Writing to File

Many developers encounter the challenge of launching an EXE from a memory buffer without the need for file creation. This article delves into the solution to this common problem, employing the CreateProcess function and a technique derived from academic research.

Windows provides the CreateProcess function, which enables the creation of new processes. The CREATE_SUSPENDED flag allows for the suspension of the process until resumed explicitly. This suspension provides the necessary time to manipulate the process's context.

The GetThreadContext function retrieves the suspended thread's context, with EBX containing a pointer to the Process Environment Block (PEB) structure. The ImageBaseAddress, which is crucial for locating the base address of the process, is stored at offset 8 within the PEB.

Once the suspended process's base address has been determined, the in-memory EXE can be loaded. If the base addresses of the in-memory EXE and the suspended process align and the in-memory EXE's size is less than or equal to the suspended process's, WriteProcessMemory can be employed to directly overwrite the suspended process's memory space.

However, additional steps are required when the aforementioned conditions are not met. The ZwUnmapViewOfSection function unmaps the original image, while VirtualAllocEx allocates sufficient memory within the suspended process's memory space. The in-memory EXE is then written to this allocated space using WriteProcessMemory.

Subsequently, BaseAddress of the in-memory EXE is patched into the PEB->ImageBaseAddress of the suspended process. The EntryPoint address of the suspended process is rewritten with the entry point of the in-memory EXE, using the EAX register of the thread context. The SetThreadContext function saves the altered thread context, and finally, ResumeThread executes the patched process.

Through this elaborate process, developers can bypass the need to write the EXE to a file and seamlessly launch it from a memory buffer, ensuring efficient and secure distribution of updates and patches.

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