Month: August 2019

Running Shellcode Directly in C

Here’s a cool thing I figured out in position-independent code. I would rephrase the title as running position-independent code instead of shellcode. Check my previous article Executing Shellcode Directly where I used a minimal PE and pointed the AddressofEntryPoint to the beginning of the PIC.

So the goal is to run shellcode in C without any function pointers or any functions at all, not even a main function 🙂 For example, this is all the code. I declare the variable name as “main”. I am using the Microsoft’s Visual C compiler with no parameters.

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char main[] =
"\x90\x90\x90\x90\x90\x90\x90\x90\x31\xdb\x64\x8b\x7b\x30\x8b\x7f"
"\x0c\x8b\x7f\x1c\x8b\x47\x08\x8b\x77\x20\x8b\x3f\x80\x7e\x0c\x33"
"\x75\xf2\x89\xc7\x03\x78\x3c\x8b\x57\x78\x01\xc2\x8b\x7a\x20\x01"
"\xc7\x89\xdd\x8b\x34\xaf\x01\xc6\x45\x81\x3e\x43\x72\x65\x61\x75"
"\xf2\x81\x7e\x08\x6f\x63\x65\x73\x75\xe9\x8b\x7a\x24\x01\xc7\x66"
"\x8b\x2c\x6f\x8b\x7a\x1c\x01\xc7\x8b\x7c\xaf\xfc\x01\xc7\x89\xd9"
"\xb1\xff\x53\xe2\xfd\x68\x63\x61\x6c\x63\x89\xe2\x52\x52\x53\x53"
"\x53\x53\x53\x53\x52\x53\xff\xd7";

After compiling it won’t of course run. Why? Well, the initialized data will end up in the “.data” section.


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Converting an EXE to a DLL

I’ve been doing some crazy experiments on running an EXE as a DLL. Here are some parts of my research.

Case #1

Let’s take a simple example like a MessageBox.

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#include <windows.h>
 
int APIENTRY wWinMain(_In_ HINSTANCE hInstance,
                     _In_opt_ HINSTANCE hPrevInstance,
                     _In_ LPWSTR    lpCmdLine,
                     _In_ int       nCmdShow)
{
MessageBox(NULL, L"@OsandaMalith", L"https://osandamalith.com", MB_ICONINFORMATION | MB_OKCANCEL);
  
}

After compiling to an EXE we have to change the characteristics under NT Header->File Header to a DLL file. I will use the value 0x2000 | 0x2| 0x100 = 0x2102.

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#define IMAGE_FILE_DLL                       0x2000  // File is a DLL.
#define IMAGE_FILE_EXECUTABLE_IMAGE          0x0002  // File is executable
#define IMAGE_FILE_32BIT_MACHINE             0x0100  // 32 bit word machine.
 
typedef struct _IMAGE_NT_HEADERS {
    DWORD Signature;
    IMAGE_FILE_HEADER FileHeader;
    IMAGE_OPTIONAL_HEADER32 OptionalHeader;
} IMAGE_NT_HEADERS32, *PIMAGE_NT_HEADERS32;
 
typedef struct _IMAGE_FILE_HEADER {
    WORD    Machine;
    WORD    NumberOfSections;
    DWORD   TimeDateStamp;
    DWORD   PointerToSymbolTable;
    DWORD   NumberOfSymbols;
    WORD    SizeOfOptionalHeader;
    WORD    Characteristics;
} IMAGE_FILE_HEADER, *PIMAGE_FILE_HEADER;

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