This module will scan the range of IP addresses for the Virtual Network Computing (VNC) servers that are accessible without any authentication details:

    msf> use auxiliary/scanner/vnc/vnc_none_auth
    msf auxiliary(vnc_none_auth) > show options
    msf auxiliary(vnc_none_auth) > set RHOSTS 10.4.124.0/24
    RHOSTS => 10.4.124.0/24
    msf auxiliary(vnc_none_auth) > run
    [*] 10.4.124.22:5900, VNC server protocol version : "RFB 004.000", 
not supported!
    [*] 10.4.124.23:5900, VNC server protocol version : "RFB 004.000", 
not supported!
    [*] 10.4.124.25:5900, VNC server protocol version : "RFB 004.000", 
not supported!
    [*] Scanned 026 of 256 hosts (010% complete)
    [*] 10.4.124.26:5900, VNC server protocol version : "RFB 004.000", 
not supported!
    [*] 10.4.124.27:5900, VNC server security types supported : None, 
free access!
    [*] 10.4.124.28:5900, VNC server security types supported : None, 
free access!
    [*] 10.4.124.29:5900, VNC server protocol version : "RFB 004.000", 
not supported!
    ...
    [*] 10.4.124.224:5900, VNC server protocol version : "RFB 004.000", 
not supported!
    [*] 10.4.124.225:5900, VNC server protocol version : "RFB 004.000", 
not supported!
    [*] 10.4.124.227:5900, VNC server security types supported : None, 
free access!
    [*] 10.4.124.228:5900, VNC server protocol version : "RFB 004.000", 
not supported!
    [*] 10.4.124.229:5900, VNC server protocol version : "RFB 004.000", 
not supported!
    [*] Scanned 231 of 256 hosts (090% complete)
    [*] Scanned 256 of 256 hosts (100% complete)
    [*] Auxiliary module execution completed
  

Note that we have found a couple of VNC servers that are accessible without authentication. This attack vector can become a serious threat for system administrators and can trivially invite unwanted guests to your VNC server from the internet if no authorization controls are enabled.