diff --git a/app/helpers/jsonld_helper.rb b/app/helpers/jsonld_helper.rb
index 957a2cbc9..dfb8fcb8b 100644
--- a/app/helpers/jsonld_helper.rb
+++ b/app/helpers/jsonld_helper.rb
@@ -61,7 +61,7 @@ module JsonLdHelper
 
   def fetch_resource_without_id_validation(uri)
     build_request(uri).perform do |response|
-      response.code == 200 ? body_to_json(response.to_s) : nil
+      response.code == 200 ? body_to_json(response.body_with_limit) : nil
     end
   end
 
diff --git a/app/lib/exceptions.rb b/app/lib/exceptions.rb
index 95e3365c2..e88e98eae 100644
--- a/app/lib/exceptions.rb
+++ b/app/lib/exceptions.rb
@@ -5,6 +5,7 @@ module Mastodon
   class NotPermittedError < Error; end
   class ValidationError < Error; end
   class HostValidationError < ValidationError; end
+  class LengthValidationError < ValidationError; end
   class RaceConditionError < Error; end
 
   class UnexpectedResponseError < Error
diff --git a/app/lib/provider_discovery.rb b/app/lib/provider_discovery.rb
index bbd3a2d43..3bec7211b 100644
--- a/app/lib/provider_discovery.rb
+++ b/app/lib/provider_discovery.rb
@@ -18,7 +18,7 @@ class ProviderDiscovery < OEmbed::ProviderDiscovery
              else
                Request.new(:get, url).perform do |res|
                  raise OEmbed::NotFound, url if res.code != 200 || res.mime_type != 'text/html'
-                 Nokogiri::HTML(res.to_s)
+                 Nokogiri::HTML(res.body_with_limit)
                end
              end
 
diff --git a/app/lib/request.rb b/app/lib/request.rb
index 8a127c65f..dca93a6e9 100644
--- a/app/lib/request.rb
+++ b/app/lib/request.rb
@@ -40,7 +40,7 @@ class Request
     end
 
     begin
-      yield response
+      yield response.extend(ClientLimit)
     ensure
       http_client.close
     end
@@ -99,6 +99,33 @@ class Request
     @http_client ||= HTTP.timeout(:per_operation, timeout).follow(max_hops: 2)
   end
 
+  module ClientLimit
+    def body_with_limit(limit = 1.megabyte)
+      raise Mastodon::LengthValidationError if content_length.present? && content_length > limit
+
+      if charset.nil?
+        encoding = Encoding::BINARY
+      else
+        begin
+          encoding = Encoding.find(charset)
+        rescue ArgumentError
+          encoding = Encoding::BINARY
+        end
+      end
+
+      contents = String.new(encoding: encoding)
+
+      while (chunk = readpartial)
+        contents << chunk
+        chunk.clear
+
+        raise Mastodon::LengthValidationError if contents.bytesize > limit
+      end
+
+      contents
+    end
+  end
+
   class Socket < TCPSocket
     class << self
       def open(host, *args)
@@ -118,5 +145,5 @@ class Request
     end
   end
 
-  private_constant :Socket
+  private_constant :ClientLimit, :Socket
 end
diff --git a/app/models/account.rb b/app/models/account.rb
index 9a83d979f..25e7d7436 100644
--- a/app/models/account.rb
+++ b/app/models/account.rb
@@ -55,7 +55,6 @@ class Account < ApplicationRecord
   include AccountHeader
   include AccountInteractions
   include Attachmentable
-  include Remotable
   include Paginable
 
   enum protocol: [:ostatus, :activitypub]
diff --git a/app/models/application_record.rb b/app/models/application_record.rb
index 71fbba5b3..83134d41a 100644
--- a/app/models/application_record.rb
+++ b/app/models/application_record.rb
@@ -2,4 +2,5 @@
 
 class ApplicationRecord < ActiveRecord::Base
   self.abstract_class = true
+  include Remotable
 end
diff --git a/app/models/concerns/account_avatar.rb b/app/models/concerns/account_avatar.rb
index 9e34a9461..2d5ebfca3 100644
--- a/app/models/concerns/account_avatar.rb
+++ b/app/models/concerns/account_avatar.rb
@@ -4,6 +4,7 @@ module AccountAvatar
   extend ActiveSupport::Concern
 
   IMAGE_MIME_TYPES = ['image/jpeg', 'image/png', 'image/gif'].freeze
+  LIMIT = 2.megabytes
 
   class_methods do
     def avatar_styles(file)
@@ -19,7 +20,8 @@ module AccountAvatar
     # Avatar upload
     has_attached_file :avatar, styles: ->(f) { avatar_styles(f) }, convert_options: { all: '-strip' }, processors: [:lazy_thumbnail]
     validates_attachment_content_type :avatar, content_type: IMAGE_MIME_TYPES
-    validates_attachment_size :avatar, less_than: 2.megabytes
+    validates_attachment_size :avatar, less_than: LIMIT
+    remotable_attachment :avatar, LIMIT
   end
 
   def avatar_original_url
diff --git a/app/models/concerns/account_header.rb b/app/models/concerns/account_header.rb
index 04c576b28..ef40b8126 100644
--- a/app/models/concerns/account_header.rb
+++ b/app/models/concerns/account_header.rb
@@ -4,6 +4,7 @@ module AccountHeader
   extend ActiveSupport::Concern
 
   IMAGE_MIME_TYPES = ['image/jpeg', 'image/png', 'image/gif'].freeze
+  LIMIT = 2.megabytes
 
   class_methods do
     def header_styles(file)
@@ -19,7 +20,8 @@ module AccountHeader
     # Header upload
     has_attached_file :header, styles: ->(f) { header_styles(f) }, convert_options: { all: '-strip' }, processors: [:lazy_thumbnail]
     validates_attachment_content_type :header, content_type: IMAGE_MIME_TYPES
-    validates_attachment_size :header, less_than: 2.megabytes
+    validates_attachment_size :header, less_than: LIMIT
+    remotable_attachment :header, LIMIT
   end
 
   def header_original_url
diff --git a/app/models/concerns/remotable.rb b/app/models/concerns/remotable.rb
index 0f18c5d96..3b8c507c3 100644
--- a/app/models/concerns/remotable.rb
+++ b/app/models/concerns/remotable.rb
@@ -3,8 +3,8 @@
 module Remotable
   extend ActiveSupport::Concern
 
-  included do
-    attachment_definitions.each_key do |attachment_name|
+  class_methods do
+    def remotable_attachment(attachment_name, limit)
       attribute_name  = "#{attachment_name}_remote_url".to_sym
       method_name     = "#{attribute_name}=".to_sym
       alt_method_name = "reset_#{attachment_name}!".to_sym
@@ -33,7 +33,7 @@ module Remotable
                         File.extname(filename)
                       end
 
-            send("#{attachment_name}=", StringIO.new(response.to_s))
+            send("#{attachment_name}=", StringIO.new(response.body_with_limit(limit)))
             send("#{attachment_name}_file_name=", basename + extname)
 
             self[attribute_name] = url if has_attribute?(attribute_name)
diff --git a/app/models/custom_emoji.rb b/app/models/custom_emoji.rb
index a77b53c98..476178e86 100644
--- a/app/models/custom_emoji.rb
+++ b/app/models/custom_emoji.rb
@@ -19,6 +19,8 @@
 #
 
 class CustomEmoji < ApplicationRecord
+  LIMIT = 50.kilobytes
+
   SHORTCODE_RE_FRAGMENT = '[a-zA-Z0-9_]{2,}'
 
   SCAN_RE = /(?<=[^[:alnum:]:]|\n|^)
@@ -29,14 +31,14 @@ class CustomEmoji < ApplicationRecord
 
   has_attached_file :image, styles: { static: { format: 'png', convert_options: '-coalesce -strip' } }
 
-  validates_attachment :image, content_type: { content_type: 'image/png' }, presence: true, size: { in: 0..50.kilobytes }
+  validates_attachment :image, content_type: { content_type: 'image/png' }, presence: true, size: { less_than: LIMIT }
   validates :shortcode, uniqueness: { scope: :domain }, format: { with: /\A#{SHORTCODE_RE_FRAGMENT}\z/ }, length: { minimum: 2 }
 
   scope :local,      -> { where(domain: nil) }
   scope :remote,     -> { where.not(domain: nil) }
   scope :alphabetic, -> { order(domain: :asc, shortcode: :asc) }
 
-  include Remotable
+  remotable_attachment :image, LIMIT
 
   def local?
     domain.nil?
diff --git a/app/models/media_attachment.rb b/app/models/media_attachment.rb
index a4d9cd9d1..ac2aa7ed2 100644
--- a/app/models/media_attachment.rb
+++ b/app/models/media_attachment.rb
@@ -56,6 +56,8 @@ class MediaAttachment < ApplicationRecord
     },
   }.freeze
 
+  LIMIT = 8.megabytes
+
   belongs_to :account, inverse_of: :media_attachments, optional: true
   belongs_to :status,  inverse_of: :media_attachments, optional: true
 
@@ -64,10 +66,9 @@ class MediaAttachment < ApplicationRecord
                     processors: ->(f) { file_processors f },
                     convert_options: { all: '-quality 90 -strip' }
 
-  include Remotable
-
   validates_attachment_content_type :file, content_type: IMAGE_MIME_TYPES + VIDEO_MIME_TYPES
-  validates_attachment_size :file, less_than: 8.megabytes
+  validates_attachment_size :file, less_than: LIMIT
+  remotable_attachment :file, LIMIT
 
   validates :account, presence: true
   validates :description, length: { maximum: 420 }, if: :local?
diff --git a/app/models/preview_card.rb b/app/models/preview_card.rb
index 86eecdfe5..0c82f06ce 100644
--- a/app/models/preview_card.rb
+++ b/app/models/preview_card.rb
@@ -26,6 +26,7 @@
 
 class PreviewCard < ApplicationRecord
   IMAGE_MIME_TYPES = ['image/jpeg', 'image/png', 'image/gif'].freeze
+  LIMIT = 1.megabytes
 
   self.inheritance_column = false
 
@@ -36,11 +37,11 @@ class PreviewCard < ApplicationRecord
   has_attached_file :image, styles: { original: { geometry: '400x400>', file_geometry_parser: FastGeometryParser } }, convert_options: { all: '-quality 80 -strip' }
 
   include Attachmentable
-  include Remotable
 
   validates :url, presence: true, uniqueness: true
   validates_attachment_content_type :image, content_type: IMAGE_MIME_TYPES
-  validates_attachment_size :image, less_than: 1.megabytes
+  validates_attachment_size :image, less_than: LIMIT
+  remotable_attachment :image, LIMIT
 
   before_save :extract_dimensions, if: :link?
 
diff --git a/app/services/fetch_atom_service.rb b/app/services/fetch_atom_service.rb
index 48ad5dcd3..62dea8298 100644
--- a/app/services/fetch_atom_service.rb
+++ b/app/services/fetch_atom_service.rb
@@ -38,13 +38,14 @@ class FetchAtomService < BaseService
     return nil if response.code != 200
 
     if response.mime_type == 'application/atom+xml'
-      [@url, { prefetched_body: response.to_s }, :ostatus]
+      [@url, { prefetched_body: response.body_with_limit }, :ostatus]
     elsif ['application/activity+json', 'application/ld+json; profile="https://www.w3.org/ns/activitystreams"'].include?(response.mime_type)
-      json = body_to_json(response.to_s)
+      body = response.body_with_limit
+      json = body_to_json(body)
       if supported_context?(json) && json['type'] == 'Person' && json['inbox'].present?
-        [json['id'], { prefetched_body: response.to_s, id: true }, :activitypub]
+        [json['id'], { prefetched_body: body, id: true }, :activitypub]
       elsif supported_context?(json) && json['type'] == 'Note'
-        [json['id'], { prefetched_body: response.to_s, id: true }, :activitypub]
+        [json['id'], { prefetched_body: body, id: true }, :activitypub]
       else
         @unsupported_activity = true
         nil
@@ -61,7 +62,7 @@ class FetchAtomService < BaseService
   end
 
   def process_html(response)
-    page = Nokogiri::HTML(response.to_s)
+    page = Nokogiri::HTML(response.body_with_limit)
 
     json_link = page.xpath('//link[@rel="alternate"]').find { |link| ['application/activity+json', 'application/ld+json; profile="https://www.w3.org/ns/activitystreams"'].include?(link['type']) }
     atom_link = page.xpath('//link[@rel="alternate"]').find { |link| link['type'] == 'application/atom+xml' }
diff --git a/app/services/fetch_link_card_service.rb b/app/services/fetch_link_card_service.rb
index 26deb5ecc..d5920a417 100644
--- a/app/services/fetch_link_card_service.rb
+++ b/app/services/fetch_link_card_service.rb
@@ -45,7 +45,7 @@ class FetchLinkCardService < BaseService
 
     Request.new(:get, @url).perform do |res|
       if res.code == 200 && res.mime_type == 'text/html'
-        @html = res.to_s
+        @html = res.body_with_limit
         @html_charset = res.charset
       else
         @html = nil
diff --git a/app/services/resolve_account_service.rb b/app/services/resolve_account_service.rb
index 034821dc0..744ea24f4 100644
--- a/app/services/resolve_account_service.rb
+++ b/app/services/resolve_account_service.rb
@@ -181,7 +181,7 @@ class ResolveAccountService < BaseService
 
     @atom_body = Request.new(:get, atom_url).perform do |response|
       raise Mastodon::UnexpectedResponseError, response unless response.code == 200
-      response.to_s
+      response.body_with_limit
     end
   end
 
diff --git a/app/workers/pubsubhubbub/confirmation_worker.rb b/app/workers/pubsubhubbub/confirmation_worker.rb
index cc2d1225b..c0e7b677e 100644
--- a/app/workers/pubsubhubbub/confirmation_worker.rb
+++ b/app/workers/pubsubhubbub/confirmation_worker.rb
@@ -57,7 +57,7 @@ class Pubsubhubbub::ConfirmationWorker
 
   def callback_get_with_params
     Request.new(:get, subscription.callback_url, params: callback_params).perform do |response|
-      @callback_response_body = response.body.to_s
+      @callback_response_body = response.body_with_limit
     end
   end
 
diff --git a/spec/lib/request_spec.rb b/spec/lib/request_spec.rb
index 4d6b20dd5..939ac006a 100644
--- a/spec/lib/request_spec.rb
+++ b/spec/lib/request_spec.rb
@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require 'rails_helper'
+require 'securerandom'
 
 describe Request do
   subject { Request.new(:get, 'http://example.com') }
@@ -64,6 +65,12 @@ describe Request do
         expect_any_instance_of(HTTP::Client).to receive(:close)
         expect { |block| subject.perform &block }.to yield_control
       end
+
+      it 'returns response which implements body_with_limit' do
+        subject.perform do |response|
+          expect(response).to respond_to :body_with_limit
+        end
+      end
     end
 
     context 'with private host' do
@@ -81,4 +88,46 @@ describe Request do
       end
     end
   end
+
+  describe "response's body_with_limit method" do
+    it 'rejects body more than 1 megabyte by default' do
+      stub_request(:any, 'http://example.com').to_return(body: SecureRandom.random_bytes(2.megabytes))
+      expect { subject.perform { |response| response.body_with_limit } }.to raise_error Mastodon::LengthValidationError
+    end
+
+    it 'accepts body less than 1 megabyte by default' do
+      stub_request(:any, 'http://example.com').to_return(body: SecureRandom.random_bytes(2.kilobytes))
+      expect { subject.perform { |response| response.body_with_limit } }.not_to raise_error
+    end
+
+    it 'rejects body by given size' do
+      stub_request(:any, 'http://example.com').to_return(body: SecureRandom.random_bytes(2.kilobytes))
+      expect { subject.perform { |response| response.body_with_limit(1.kilobyte) } }.to raise_error Mastodon::LengthValidationError
+    end
+
+    it 'rejects too large chunked body' do
+      stub_request(:any, 'http://example.com').to_return(body: SecureRandom.random_bytes(2.megabytes), headers: { 'Transfer-Encoding' => 'chunked' })
+      expect { subject.perform { |response| response.body_with_limit } }.to raise_error Mastodon::LengthValidationError
+    end
+
+    it 'rejects too large monolithic body' do
+      stub_request(:any, 'http://example.com').to_return(body: SecureRandom.random_bytes(2.megabytes), headers: { 'Content-Length' => 2.megabytes })
+      expect { subject.perform { |response| response.body_with_limit } }.to raise_error Mastodon::LengthValidationError
+    end
+
+    it 'uses binary encoding if Content-Type does not tell encoding' do
+      stub_request(:any, 'http://example.com').to_return(body: '', headers: { 'Content-Type' => 'text/html' })
+      expect(subject.perform { |response| response.body_with_limit.encoding }).to eq Encoding::BINARY
+    end
+
+    it 'uses binary encoding if Content-Type tells unknown encoding' do
+      stub_request(:any, 'http://example.com').to_return(body: '', headers: { 'Content-Type' => 'text/html; charset=unknown' })
+      expect(subject.perform { |response| response.body_with_limit.encoding }).to eq Encoding::BINARY
+    end
+
+    it 'uses encoding specified by Content-Type' do
+      stub_request(:any, 'http://example.com').to_return(body: '', headers: { 'Content-Type' => 'text/html; charset=UTF-8' })
+      expect(subject.perform { |response| response.body_with_limit.encoding }).to eq Encoding::UTF_8
+    end
+  end
 end
diff --git a/spec/models/concerns/remotable_spec.rb b/spec/models/concerns/remotable_spec.rb
index 0b2dad23f..b39233739 100644
--- a/spec/models/concerns/remotable_spec.rb
+++ b/spec/models/concerns/remotable_spec.rb
@@ -29,7 +29,10 @@ RSpec.describe Remotable do
 
   context 'Remotable module is included' do
     before do
-      class Foo; include Remotable; end
+      class Foo
+        include Remotable
+        remotable_attachment :hoge, 1.kilobyte
+      end
     end
 
     let(:attribute_name) { "#{hoge}_remote_url".to_sym }