Since the dawn of computing in the '80s and '90s, hackers—once simply known as developers and coders—have pursued the ultimate bootkit/rootkit subversion method. The approach proposed here represents only a fragment of the broader concept. Can we craft specialized shellcode capable of embedding itself into the OS layer, then tunneling indirectly down into the BIOS, ultimately resurfacing within the kernel? Theoretically sound, this hypothesis aims to commandeer the entire boot process, traversing through BIOS and returning seamlessly into the system kernel, thereby enabling a persistent, continuous, and advanced shell environment.

The described method s below are an advanced, multi-stage bootkit-style technique intended for safely placing a file (bootres.dll) into the \Windows\system32 directory upon the next reboot in Legacy BIOS/MBR Windows systems. It leverages multiple boot stages to bypass the complexities of directly interacting with Windows file systems.

             High-Level Software Layers
+-----------------------------------------------------+
|                User Applications                    |
|        (Browsers, Editors, Games, etc.)             |
+-----------------------------------------------------+
|                Operating System (OS)                |
|     (System APIs, Libraries, User Interfaces)       |
+-----------------------------------------------------+
|                   OS Kernel                         |
| (Process Scheduling, Memory Management, Device I/O) |
+-----------------------------------------------------+
|            Drivers & Kernel Modules                 |
|        (Device Drivers, File Systems, etc.)         |
+-----------------------------------------------------+
|                  Bootloader                         |
|      (Stage 2 Bootkit Core, Patched Snippet)        |
+-----------------------------------------------------+
|           Master Boot Record (MBR)                  |
|            (Stage 1 - Minimal Loader)               |
+-----------------------------------------------------+
|                 BIOS Firmware                       |
|           (POST, Hardware Initialization)           |
+-----------------------------------------------------+
|                 Physical Memory                     |
|              (RAM, ROM, Cache, etc.)                |
+-----------------------------------------------------+
|                     Hardware                        |
|        (CPU, Disk, Peripherals, Interfaces)         |
+-----------------------------------------------------+

This document outlines a minimal "Hello World" chainloader example alongside an advanced conceptual bootkit-style hook method, intended to demonstrate safely placing a file (bootres.dll) into the \Windows\system32 directory upon reboot in Legacy BIOS/MBR Windows systems.

• Minimal code footprint (≤466 bytes).

• Prints a simple message for feedback.

• Loads the next stage from hidden sectors.

• Identifies and patches early Windows boot files (bootmgr, winload.exe, or older loaders).

• Injects custom code snippet ("hook") directly into the identified bootloader.

• Transfers control seamlessly to Windows' original Volume Boot Record.

• Executes during early Windows boot.

• Safely places or replaces bootres.dll in \Windows\system32.

• Optionally cleans itself or remains persistent.

• Intended for educational or controlled environments only.

• Requires careful handling due to ethical, security, and technical complexities.

• Modern protections like Secure Boot and NTFS complexity present significant implementation challenges.

This combined approach demonstrates both a basic understanding of bootloader operations and an advanced conceptual grasp of boot processes, filesystem interactions, and persistence strategies.

Warning: This is educational code. Writing this to your real hard drive MBR could corrupt your system if something goes wrong. Use a VM or backup first.

nasm -f bin custom_mbr.asm -o custom_mbr.bin

Then (VERY DANGEROUS):

dd if=custom_mbr.bin of=/dev/sdX bs=512 count=1

(Replace sdX with correct disk; do NOT do this on a live system unless you know exactly what you’re doing.)

1. Displays a short text line via BIOS interrupt 0x10.

2. Locates the active partition in the partition table.

3. Loads the first sector of that partition (the Volume Boot Record) to memory address 0x7E00:0000.

4. Jumps there, allowing Windows (or any OS) to continue booting.

Note:

• The last two bytes must be 0x55, 0xAA to mark the sector as bootable for a BIOS system.

• Key Offsets:

  • Partition table starts at 0x1BE

  • Boot signature at 0x1FE (the last two bytes of the 512-byte sector)

[org 0x7C00]          ; BIOS loads the MBR at 0x0000:0x7C00
bits 16

start:
    xor ax, ax
    mov ss, ax
    mov sp, 0x7C00

    mov ds, ax

    mov si, hello_message
    call print_string

    mov bx, PARTITION_TABLE_OFFSET
    mov cx, 4
find_active_partition:
    push cx
    mov al, [bx]
    cmp al, 0x80
    je partition_found

    add bx, 16
    pop cx
    loop find_active_partition

no_active_partition:
    call print_line
    mov si, error_no_active
    call print_string
    jmp halt

partition_found:
    mov dl, [BOOT_DRIVE]

    mov dh, [bx+1]
    mov cl, [bx+2]
    mov ch, [bx+3]
    mov [part_head], dh
    mov [part_sector], cl
    mov [part_cyl], ch

    call read_vbr

    jmp 0x7E0:0x0000

read_vbr:
    mov ax, 0x7E0
    mov es, ax
    xor bx, bx

    mov ah, 0x02
    mov al, 1
    mov ch, [part_cyl]
    mov cl, [part_sector]
    mov dh, [part_head]
    int 0x13

    ret

print_string:
.next_char:
    lodsb
    or al, al
    jz .done
    mov ah, 0x0E
    int 0x10
    jmp .next_char
.done:
    ret

print_line:
    mov ah, 0x0E
    mov al, 0x0D
    int 0x10
    mov al, 0x0A
    int 0x10
    ret

halt:
    cli
    hlt
    jmp halt

hello_message db "Custom MBR: Hello from the boot sector!", 0
error_no_active db "No active partition found! System halted.", 0

part_head   db 0
part_sector db 0
part_cyl    db 0

BOOT_DRIVE db 0x80

PARTITION_TABLE_OFFSET equ 0x1BE

; Fill up to 510 bytes with zeros
times 510 - ($-$$) db 0

; Bootable sector signature
dw 0xAA55

Important Security & Ethical Note:
Modifying Windows’ boot sequence or hooking OS components can be malicious if done without authorization. Always conduct such experiments in controlled environments (e.g., VMs).

Rather than placing bootres.dll directly into the root (C:\), use a multi-stage bootkit-style hook to ensure the file ends up in \Windows\system32 during the next boot on Legacy BIOS/MBR systems.

• Print message.

• Load Stage 2 using INT 0x13 (AH=0x42 for large disks or AH=0x02 for CHS addressing).

• Maintain partition table integrity (offset 0x1BE).

• Mark bootable with 0x55AA at offset 0x1FE.

• Parses active partition to locate \bootmgr, \Boot\BCD, or older loaders (NTLDR).

• Implements minimal filesystem parsing (FAT32 easier; NTFS complex).

• Patches identified Windows bootloader file with injected code:

  • Allocates space or utilizes existing code cave.

  • Modifies bootloader to run custom snippet.

• Chains to original Windows VBR.

• Runs within Windows' early loader environment, enabling proper filesystem access.

• Creates or replaces \Windows\system32\bootres.dll with desired content (e.g., copy /b bootres.dll+newlogo-decoded.bmp patched-bootres.dll).

• Closes file, returning execution to Windows boot.

• INT 13h Hook: Effective temporarily; limited by Windows drivers.

• Early Driver Injection: Modify registry or BCD to load custom driver at boot.

• Digital Signatures/Secure Boot: Modern systems may block modifications.

• Filesystem Complexity (NTFS vs. FAT32): NTFS demands sophisticated parsing.

• Persistence & Space Constraints: Limited MBR size (466 bytes); Stage 2 stored separately.

[Power On / BIOS]  
        ↓  
[MBR (Stage 1)]  
   - Message display  
   - Load Stage 2  
        ↓  
[Stage 2]  
   - Locate & patch bootloader  
   - Chain-load Windows VBR  
        ↓  
[Windows Bootloader]  
   - Hook executes  
   - Creates `bootres.dll` in `\Windows\system32`  
   - Continues booting Windows

• Always test in a controlled VM environment.

• Modern protections (UEFI/Secure Boot) significantly complicate or prevent this approach.

• Even partial implementation demonstrates advanced understanding of bootkit concepts.

// ============================================================================= //
//    _____                      __       _____       _____ __             __  
//   / ___/____ ___  ____ ______/ /_     /__  /      / ___// /_____ ______/ /__
//   \__ \/ __ `__ \/ __ `/ ___/ __ \______/ / ______\__ \/ __/ __ `/ ___/ //_/
//  ___/ / / / / / / /_/ (__  ) / / /_____/ /_/_____/__/ / /_/ /_/ / /__/ ,<   
// ____/_/ /_/ /_/\__,_/____/_/ /_/     /____/    /____/\__/\__,_/\___/_/|_|                                                                                                        
// ==================================================== //
//                                                  
//          Tribute to "Smashing the Stack"        
//      and the original hackers who paved the way. 
//                                                  
//     [ Aleph One ] [ Levy ] [ Condor ]          
//   [ L0pht ] [ CDC ] [ Phrack ] [ 2600 ]         
//                                                  
// ================================================= //
//                                                  
//     "Because security is an illusion,           
//             and knowledge is power."             
//                                                  
// ================================================= //