CVE-2022-3222 Verificación del comportamiento de serialización de ActiveRecord

• https://discuss.rubyonrails.org/t/cve-2022-32224-possible-rce-escalation-bug-with-serialized-columns-in-active-record/81017
• https://api.rubyonrails.org/classes/ActiveRecord/AttributeMethods/Serialization/ClassMethods.html
• https://github.com/rails/rails/pull/45584

Preparación

bundle install

bin/rails db:migrate

Modelo

bin/rails generate model User values:string

class User < ApplicationRecord
  serialize :values, Array
end

Verificación de funcionamiento

Serializar y guardar un array

❯ bundle exec rails c
Loading development environment (Rails 7.0.3.1)
irb(main):001:0> User.create(values: [16 * 16, "ffff"])
   (0.6ms)  SELECT sqlite_version(*)
  TRANSACTION (0.0ms)  begin transaction
  User Create (0.6ms)  INSERT INTO "users" ("values", "created_at", "updated_at") VALUES (?, ?, ?)  [["values", "---\n- 256\n- ffff\n"], ["created_at", "2022-07-17 07:46:18.593587"], ["updated_at", "2022-07-17 07:46:18.593587"]]
  TRANSACTION (0.4ms)  commit transaction
=>
#<User:0x0000000105ee1a78
 id: 3,
 values: [256, "ffff"],
 created_at: Sun, 17 Jul 2022 07:46:18.593587000 UTC +00:00,
 updated_at: Sun, 17 Jul 2022 07:46:18.593587000 UTC +00:00>

irb(main):002:0> User.last.values
  User Load (0.5ms)  SELECT "users".* FROM "users" ORDER BY "users"."id" DESC LIMIT ?  [["LIMIT", 1]]
=> [256, "ffff"]

Dado que se especifica Array como class_name_or_coder, no se puede pasar una cadena tal cual

irb(main):001:0> User.create(values: 'aaa')
   (0.6ms)  SELECT sqlite_version(*)
.../activerecord-7.0.3.1/lib/active_record/coders/yaml_column.rb:36:in `assert_valid_value': can't serialize `values`: was supposed to be a Array, but was a String. -- "aaa" (ActiveRecord::SerializationTypeMismatch)

Actualización

irb(main):001:0> user = User.create!(values: ["aaa"])
   (0.6ms)  SELECT sqlite_version(*)
  TRANSACTION (0.0ms)  begin transaction
  User Create (0.4ms)  INSERT INTO "users" ("values", "created_at", "updated_at") VALUES (?, ?, ?)  [["values", "---\n- aaa\n"], ["created_at", "2022-07-17 11:50:58.515968"], ["updated_at", "2022-07-17 11:50:58.515968"]]
  TRANSACTION (0.4ms)  commit transaction
=>
#<User:0x00000001057b65a0
...
irb(main):002:0> user.update_column(:values, ["aaaa"])
  User Update (0.9ms)  UPDATE "users" SET "values" = ? WHERE "users"."id" = ?  [["values", "---\n- aaaa\n"], ["id", 8]]
=> true
irb(main):003:0> user.update_attribute(:values, ["fffff"])
  TRANSACTION (0.1ms)  begin transaction
  User Update (0.5ms)  UPDATE "users" SET "values" = ?, "updated_at" = ? WHERE "users"."id" = ?  [["values", "---\n- fffff\n"], ["updated_at", "2022-07-17 11:52:01.795259"], ["id", 8]]
  TRANSACTION (1.0ms)  commit transaction
=> true
irb(main):004:0> user.update(values: ["aaaddd"])
  TRANSACTION (0.1ms)  begin transaction
  User Update (0.7ms)  UPDATE "users" SET "values" = ?, "updated_at" = ? WHERE "users"."id" = ?  [["values", "---\n- aaaddd\n"], ["updated_at", "2022-07-17 11:52:25.306288"], ["id", 8]]
  TRANSACTION (1.1ms)  commit transaction
=> true

Serialización/deserialización de cadenas que contienen ", ' y saltos de línea

irb(main):001:0> User.create(values: ["'", '"', {'"' => [{"aaa" => "aa\na\r"}]}])
   (0.6ms)  SELECT sqlite_version(*)
  TRANSACTION (0.0ms)  begin transaction
  User Create (0.7ms)  INSERT INTO "users" ("values", "created_at", "updated_at") VALUES (?, ?, ?)  [["values", "---\n- \"'\"\n- \"\\\"\"\n- \"\\\"\":\n  - aaa: \"aa\\na\\r\"\n"], ["created_at", "2022-07-17 07:50:43.091916"], ["updated_at", "2022-07-17 07:50:43.091916"]]
  TRANSACTION (0.4ms)  commit transaction
=>
#<User:0x000000010dfb3cc8
 id: 4,
 values: ["'", "\"", {"\""=>[{"aaa"=>"aa\na\r"}]}],
 created_at: Sun, 17 Jul 2022 07:50:43.091916000 UTC +00:00,
 updated_at: Sun, 17 Jul 2022 07:50:43.091916000 UTC +00:00>

irb(main):002:0> User.last.values
  User Load (0.4ms)  SELECT "users".* FROM "users" ORDER BY "users"."id" DESC LIMIT ?  [["LIMIT", 1]]
=> ["'", "\"", {"\""=>[{"aaa"=>"aa\na\r"}]}]

Restauración de clases arbitrarias

En 7.0.3 se puede guardar cualquier clase mediante serialización y deserializarla al cargar

❯ bundle exec rails c
Loading development environment (Rails 7.0.3)
irb(main):001:0> gemspec = Gem::Specification.new("test")
=>
Gem::Specification.new do |s|
...
irb(main):002:0>
irb(main):003:0> user = User.create!(values: [gemspec])
   (0.5ms)  SELECT sqlite_version(*)
  TRANSACTION (0.1ms)  begin transaction
  User Create (0.4ms)  INSERT INTO "users" ("values", "created_at", "updated_at") VALUES (?, ?, ?)  [["values", "---\n- !ruby/object:Gem::Specification\n  name: test\n  version:\n  platform: ruby\n  authors: []\n  autorequire:\n  bindir: bin\n  cert_chain: []\n  date: 2022-07-17 00:00:00.000000000 Z\n  dependencies: []\n  description:\n  email:\n  executables: []\n  extensions: []\n  extra_rdoc_files: []\n  files: []\n  homepage:\n  licenses: []\n  metadata: {}\n  post_install_message:\n  rdoc_options: []\n  require_paths:\n  - lib\n  required_ruby_version: !ruby/object:Gem::Requirement\n    requirements:\n    - &1\n      - \">=\"\n      - !ruby/object:Gem::Version\n        version: '0'\n  required_rubygems_version: !ruby/object:Gem::Requirement\n    requirements:\n    - *1\n  requirements: []\n  rubygems_version: 3.3.7\n  signing_key:\n  specification_version: 4\n  summary:\n  test_files: []\n"], ["created_at", "2022-07-17 12:08:19.272191"], ["updated_at", "2022-07-17 12:08:19.272191"]]
  TRANSACTION (0.9ms)  commit transaction
=>
#<User:0x00000001171ea3a8
...
irb(main):004:0>
irb(main):005:0> User.last.values
  User Load (0.3ms)  SELECT "users".* FROM "users" ORDER BY "users"."id" DESC LIMIT ?  [["LIMIT", 1]]
=>
[Gem::Specification.new do |s|
   s.name = "test"
   s.version = nil
   s.installed_by_version = Gem::Version.new("0")
   s.date = Time.utc(2022, 7, 17)
   s.require_paths = ["lib"]
   s.rubygems_version = "3.3.7"
   s.specification_version = 4
   s.summary = nil
   end]

En 7.0.3.1, tanto guardar como cargar producen un error

❯ bundle exec rails c
Loading development environment (Rails 7.0.3.1)
irb(main):001:0> User.last.values
   (1.0ms)  SELECT sqlite_version(*)
  User Load (0.4ms)  SELECT "users".* FROM "users" ORDER BY "users"."id" DESC LIMIT ?  [["LIMIT", 1]]
.../psych/class_loader.rb:99:in `find': Tried to load unspecified class: Gem::Specification (Psych::DisallowedClass)

irb(main):002:0> gemspec = Gem::Specification.new("test")
=>
Gem::Specification.new do |s|
...

irb(main):003:0> user = User.create!(values: [gemspec])
  TRANSACTION (0.1ms)  begin transaction
  TRANSACTION (0.0ms)  rollback transaction
.../psych/class_loader.rb:99:in `find': Tried to load unspecified class: Gem::Specification (Psych::DisallowedClass)
.../psych/class_loader.rb:99:in `find': Tried to load unspecified class: Gem::Specification (Psych::DisallowedClass)

Incluso en 7.0.3, si se intenta guardar una instancia de ActiveSupport::Deprecation::DeprecatedInstanceVariableProxy, se produce un error y no funciona

.../psych/visitors/emitter.rb:32:in `scalar': wrong argument type ActiveSupport::Deprecation::DeprecatedInstanceVariableProxy (expected String) (TypeError)

Guardar símbolos

En 7.0.3 se puede guardar