Add support for using a Camo proxy server

User images and videos will get proxied through
the Camo server in order to keep malicious
sites from collecting the IP address of users.

33 files changed, 591 insertions, 16 deletions

diff --git a/app/helpers/application_settings_helper.rb b/app/helpers/application_settings_helper.rb
index 0ab19f1d2d2..c2d7350ce12 100644
--- a/app/helpers/application_settings_helper.rb
+++ b/app/helpers/application_settings_helper.rb
@@ -164,6 +164,10 @@ module ApplicationSettingsHelper
       :allow_local_requests_from_system_hooks,
       :dns_rebinding_protection_enabled,
       :archive_builds_in_human_readable,
+      :asset_proxy_enabled,
+      :asset_proxy_secret_key,
+      :asset_proxy_url,
+      :asset_proxy_whitelist,
       :authorized_keys_enabled,
       :auto_devops_enabled,
       :auto_devops_domain,
diff --git a/app/models/application_setting.rb b/app/models/application_setting.rb
index 2a99c6e5c59..92004b92647 100644
--- a/app/models/application_setting.rb
+++ b/app/models/application_setting.rb
@@ -18,12 +18,19 @@ class ApplicationSetting < ApplicationRecord
   # fix a lot of tests using allow_any_instance_of
   include ApplicationSettingImplementation
 
+  attr_encrypted :asset_proxy_secret_key,
+                 mode: :per_attribute_iv,
+                 insecure_mode: true,
+                 key: Settings.attr_encrypted_db_key_base_truncated,
+                 algorithm: 'aes-256-cbc'
+
   serialize :restricted_visibility_levels # rubocop:disable Cop/ActiveRecordSerialize
   serialize :import_sources # rubocop:disable Cop/ActiveRecordSerialize
   serialize :disabled_oauth_sign_in_sources, Array # rubocop:disable Cop/ActiveRecordSerialize
   serialize :domain_whitelist, Array # rubocop:disable Cop/ActiveRecordSerialize
   serialize :domain_blacklist, Array # rubocop:disable Cop/ActiveRecordSerialize
   serialize :repository_storages # rubocop:disable Cop/ActiveRecordSerialize
+  serialize :asset_proxy_whitelist, Array # rubocop:disable Cop/ActiveRecordSerialize
 
   ignore_column :koding_url
   ignore_column :koding_enabled
@@ -192,6 +199,17 @@ class ApplicationSetting < ApplicationRecord
             allow_nil: true,
             numericality: { only_integer: true, greater_than_or_equal_to: 0, less_than: 65536 }
 
+  validates :asset_proxy_url,
+            presence: true,
+            allow_blank: false,
+            url: true,
+            if: :asset_proxy_enabled?
+
+  validates :asset_proxy_secret_key,
+            presence: true,
+            allow_blank: false,
+            if: :asset_proxy_enabled?
+
   SUPPORTED_KEY_TYPES.each do |type|
     validates :"#{type}_key_restriction", presence: true, key_restriction: { type: type }
   end
diff --git a/app/models/application_setting_implementation.rb b/app/models/application_setting_implementation.rb
index 55ac1e129cf..a6dd9986e23 100644
--- a/app/models/application_setting_implementation.rb
+++ b/app/models/application_setting_implementation.rb
@@ -23,8 +23,9 @@ module ApplicationSettingImplementation
         akismet_enabled: false,
         allow_local_requests_from_web_hooks_and_services: false,
         allow_local_requests_from_system_hooks: true,
-        dns_rebinding_protection_enabled: true,
+        asset_proxy_enabled: false,
         authorized_keys_enabled: true, # TODO default to false if the instance is configured to use AuthorizedKeysCommand
+        commit_email_hostname: default_commit_email_hostname,
         container_registry_token_expire_delay: 5,
         default_artifacts_expire_in: '30 days',
         default_branch_protection: Settings.gitlab['default_branch_protection'],
@@ -33,7 +34,9 @@ module ApplicationSettingImplementation
         default_project_visibility: Settings.gitlab.default_projects_features['visibility_level'],
         default_projects_limit: Settings.gitlab['default_projects_limit'],
         default_snippet_visibility: Settings.gitlab.default_projects_features['visibility_level'],
+        diff_max_patch_bytes: Gitlab::Git::Diff::DEFAULT_MAX_PATCH_BYTES,
         disabled_oauth_sign_in_sources: [],
+        dns_rebinding_protection_enabled: true,
         domain_whitelist: Settings.gitlab['domain_whitelist'],
         dsa_key_restriction: 0,
         ecdsa_key_restriction: 0,
@@ -52,9 +55,11 @@ module ApplicationSettingImplementation
         housekeeping_gc_period: 200,
         housekeeping_incremental_repack_period: 10,
         import_sources: Settings.gitlab['import_sources'],
+        local_markdown_version: 0,
         max_artifacts_size: Settings.artifacts['max_size'],
         max_attachment_size: Settings.gitlab['max_attachment_size'],
         mirror_available: true,
+        outbound_local_requests_whitelist: [],
         password_authentication_enabled_for_git: true,
         password_authentication_enabled_for_web: Settings.gitlab['signin_enabled'],
         performance_bar_allowed_group_id: nil,
@@ -63,6 +68,8 @@ module ApplicationSettingImplementation
         plantuml_url: nil,
         polling_interval_multiplier: 1,
         project_export_enabled: true,
+        protected_ci_variables: false,
+        raw_blob_request_limit: 300,
         recaptcha_enabled: false,
         repository_checks_enabled: true,
         repository_storages: ['default'],
@@ -95,16 +102,10 @@ module ApplicationSettingImplementation
         user_default_internal_regex: nil,
         user_show_add_ssh_key_message: true,
         usage_stats_set_by_user_id: nil,
-        diff_max_patch_bytes: Gitlab::Git::Diff::DEFAULT_MAX_PATCH_BYTES,
-        commit_email_hostname: default_commit_email_hostname,
         snowplow_collector_hostname: nil,
         snowplow_cookie_domain: nil,
         snowplow_enabled: false,
-        snowplow_site_id: nil,
-        protected_ci_variables: false,
-        local_markdown_version: 0,
-        outbound_local_requests_whitelist: [],
-        raw_blob_request_limit: 300
+        snowplow_site_id: nil
       }
     end
 
@@ -198,6 +199,15 @@ module ApplicationSettingImplementation
     end
   end
 
+  def asset_proxy_whitelist=(values)
+    values = domain_strings_to_array(values) if values.is_a?(String)
+
+    # make sure we always whitelist the running host
+    values << Gitlab.config.gitlab.host unless values.include?(Gitlab.config.gitlab.host)
+
+    self[:asset_proxy_whitelist] = values
+  end
+
   def repository_storages
     Array(read_attribute(:repository_storages))
   end
@@ -306,6 +316,7 @@ module ApplicationSettingImplementation
 
     values
       .split(DOMAIN_LIST_SEPARATOR)
+      .map(&:strip)
       .reject(&:empty?)
       .uniq
   end
diff --git a/app/services/application_settings/update_service.rb b/app/services/application_settings/update_service.rb
index 471df6e2d0c..03ff282dec5 100644
--- a/app/services/application_settings/update_service.rb
+++ b/app/services/application_settings/update_service.rb
@@ -6,6 +6,8 @@ module ApplicationSettings
 
     attr_reader :params, :application_setting
 
+    MARKDOWN_CACHE_INVALIDATING_PARAMS = %w(asset_proxy_enabled asset_proxy_url asset_proxy_secret_key asset_proxy_whitelist).freeze
+
     def execute
       validate_classification_label(application_setting, :external_authorization_service_default_label)
 
@@ -25,7 +27,13 @@ module ApplicationSettings
         params[:usage_stats_set_by_user_id] = current_user.id
       end
 
-      @application_setting.update(@params)
+      @application_setting.assign_attributes(params)
+
+      if invalidate_markdown_cache?
+        @application_setting[:local_markdown_version] = @application_setting.local_markdown_version + 1
+      end
+
+      @application_setting.save
     end
 
     private
@@ -41,6 +49,11 @@ module ApplicationSettings
       @application_setting.add_to_outbound_local_requests_whitelist(values_array)
     end
 
+    def invalidate_markdown_cache?
+      !params.key?(:local_markdown_version) &&
+        (@application_setting.changes.keys & MARKDOWN_CACHE_INVALIDATING_PARAMS).any?
+    end
+
     def update_terms(terms)
       return unless terms.present?
 
diff --git a/changelogs/unreleased/security-enable-image-proxy.yml b/changelogs/unreleased/security-enable-image-proxy.yml
new file mode 100644
index 00000000000..88b49ffd9e8
--- /dev/null
+++ b/changelogs/unreleased/security-enable-image-proxy.yml
@@ -0,0 +1,5 @@
+---
+title: Added image proxy to mitigate potential stealing of IP addresses
+merge_request:
+author:
+type: security
diff --git a/config/initializers/asset_proxy_settings.rb b/config/initializers/asset_proxy_settings.rb
new file mode 100644
index 00000000000..92247aba1b8
--- /dev/null
+++ b/config/initializers/asset_proxy_settings.rb
@@ -0,0 +1,6 @@
+#
+# Asset proxy settings
+#
+ActiveSupport.on_load(:active_record) do
+  Banzai::Filter::AssetProxyFilter.initialize_settings
+end
diff --git a/config/initializers/fill_shards.rb b/config/initializers/fill_shards.rb
index 18e067c8854..cad662e12f3 100644
--- a/config/initializers/fill_shards.rb
+++ b/config/initializers/fill_shards.rb
@@ -1,3 +1,5 @@
-if Shard.connected? && !Gitlab::Database.read_only?
+# The `table_exists?` check is needed because during our migration rollback testing,
+# `Shard.connected?` could be cached and return true even though the table doesn't exist
+if Shard.connected? && Shard.table_exists? && !Gitlab::Database.read_only?
   Shard.populate!
 end
diff --git a/db/migrate/20190219201635_add_asset_proxy_settings.rb b/db/migrate/20190219201635_add_asset_proxy_settings.rb
new file mode 100644
index 00000000000..beeb6400292
--- /dev/null
+++ b/db/migrate/20190219201635_add_asset_proxy_settings.rb
@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+class AddAssetProxySettings < ActiveRecord::Migration[5.0]
+  include Gitlab::Database::MigrationHelpers
+
+  # Set this constant to true if this migration requires downtime.
+  DOWNTIME = false
+
+  def change
+    add_column :application_settings, :asset_proxy_enabled, :boolean, default: false, null: false
+    add_column :application_settings, :asset_proxy_url, :string
+    add_column :application_settings, :asset_proxy_whitelist, :text
+    add_column :application_settings, :encrypted_asset_proxy_secret_key, :text
+    add_column :application_settings, :encrypted_asset_proxy_secret_key_iv, :string
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index 944d23e5365..7e5e96707dc 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -278,6 +278,11 @@ ActiveRecord::Schema.define(version: 2019_08_15_093949) do
     t.boolean "allow_local_requests_from_system_hooks", default: true, null: false
     t.bigint "instance_administration_project_id"
     t.string "snowplow_collector_hostname"
+    t.boolean "asset_proxy_enabled", default: false, null: false
+    t.string "asset_proxy_url"
+    t.text "asset_proxy_whitelist"
+    t.text "encrypted_asset_proxy_secret_key"
+    t.string "encrypted_asset_proxy_secret_key_iv"
     t.index ["custom_project_templates_group_id"], name: "index_application_settings_on_custom_project_templates_group_id"
     t.index ["file_template_project_id"], name: "index_application_settings_on_file_template_project_id"
     t.index ["instance_administration_project_id"], name: "index_applicationsettings_on_instance_administration_project_id"
diff --git a/doc/api/settings.md b/doc/api/settings.md
index 710b63c9a2f..e3d8fe68e08 100644
--- a/doc/api/settings.md
+++ b/doc/api/settings.md
@@ -68,6 +68,9 @@ Example response:
    "allow_local_requests_from_hooks_and_services": true,
    "allow_local_requests_from_web_hooks_and_services": true,
    "allow_local_requests_from_system_hooks": false
+   "asset_proxy_enabled": true,
+   "asset_proxy_url": "https://assets.example.com",
+   "asset_proxy_whitelist": ["example.com", "*.example.com", "your-instance.com"]
 }
 ```
 
@@ -141,6 +144,9 @@ Example response:
   "user_show_add_ssh_key_message": true,
   "file_template_project_id": 1,
   "local_markdown_version": 0,
+  "asset_proxy_enabled": true,
+  "asset_proxy_url": "https://assets.example.com",
+  "asset_proxy_whitelist": ["example.com", "*.example.com", "your-instance.com"],
   "geo_node_allowed_ips": "0.0.0.0/0, ::/0",
   "allow_local_requests_from_hooks_and_services": true,
   "allow_local_requests_from_web_hooks_and_services": true,
@@ -186,6 +192,10 @@ are listed in the descriptions of the relevant settings.
 | `allow_local_requests_from_hooks_and_services` | boolean    | no                                   | (Deprecated: Use `allow_local_requests_from_web_hooks_and_services` instead) Allow requests to the local network from hooks and services. |
 | `allow_local_requests_from_web_hooks_and_services` | boolean    | no                                   | Allow requests to the local network from web hooks and services. |
 | `allow_local_requests_from_system_hooks` | boolean    | no                                   | Allow requests to the local network from system hooks. |
+| `asset_proxy_enabled`                    | boolean          | no                                   | (**If enabled, requires:** `asset_proxy_url`) Enable proxying of assets. GitLab restart is required to apply changes. |
+| `asset_proxy_secret_key`                 | string           | no                                   | Shared secret with the asset proxy server. GitLab restart is required to apply changes. |
+| `asset_proxy_url`                        | string           | no                                   | URL of the asset proxy server. GitLab restart is required to apply changes. |
+| `asset_proxy_whitelist`                  | string or array of strings | no                         | Assets that match these domain(s) will NOT be proxied. Wildcards allowed. Your GitLab installation URL is automatically whitelisted. GitLab restart is required to apply changes. |
 | `authorized_keys_enabled`                | boolean          | no                                   | By default, we write to the `authorized_keys` file to support Git over SSH without additional configuration. GitLab can be optimized to authenticate SSH keys via the database file. Only disable this if you have configured your OpenSSH server to use the AuthorizedKeysCommand. |
 | `auto_devops_domain`                     | string           | no                                   | Specify a domain to use by default for every project's Auto Review Apps and Auto Deploy stages. |
 | `auto_devops_enabled`                    | boolean          | no                                   | Enable Auto DevOps for projects by default. It will automatically build, test, and deploy applications based on a predefined CI/CD configuration. |
diff --git a/doc/security/README.md b/doc/security/README.md
index 5d498ac7602..fa34f07060e 100644
--- a/doc/security/README.md
+++ b/doc/security/README.md
@@ -17,3 +17,4 @@ type: index
 - [Enforce Two-factor authentication](two_factor_authentication.md)
 - [Send email confirmation on sign-up](user_email_confirmation.md)
 - [Security of running jobs](https://docs.gitlab.com/runner/security/)
+- [Proxying images](asset_proxy.md)
diff --git a/doc/security/asset_proxy.md b/doc/security/asset_proxy.md
new file mode 100644
index 00000000000..f25910d3db7
--- /dev/null
+++ b/doc/security/asset_proxy.md
@@ -0,0 +1,28 @@
+A possible security concern when managing a public facing GitLab instance is
+the ability to steal a users IP address by referencing images in issues, comments, etc.
+
+For example, adding `![Example image](http://example.com/example.png)` to
+an issue description will cause the image to be loaded from the external
+server in order to be displayed.  However this also allows the external server
+to log the IP address of the user.
+
+One way to mitigate this is by proxying any external images to a server you
+control.  GitLab handles this by allowing you to run the "Camo" server
+[cactus/go-camo](https://github.com/cactus/go-camo#how-it-works).
+The image request is sent to the Camo server, which then makes the request for
+the original image.  This way an attacker only ever seems the IP address
+of your Camo server.
+
+Once you have your Camo server up and running, you can configure GitLab to
+proxy image requests to it.  The following settings are supported:
+
+| Attribute                | Description |
+| ------------------------ | ----------- |
+| `asset_proxy_enabled`    | (**If enabled, requires:** `asset_proxy_url`) Enable proxying of assets. |
+| `asset_proxy_secret_key` | Shared secret with the asset proxy server. |
+| `asset_proxy_url`        | URL of the asset proxy server. |
+| `asset_proxy_whitelist`  | Assets that match these domain(s) will NOT be proxied. Wildcards allowed. Your GitLab installation URL is automatically whitelisted. |
+
+These can be set via the [Application setting API](../api/settings.md)
+
+Note that a GitLab restart is required to apply any changes.
diff --git a/lib/api/entities.rb b/lib/api/entities.rb
index 5e66b4e76a5..e5df4574bc4 100644
--- a/lib/api/entities.rb
+++ b/lib/api/entities.rb
@@ -1174,6 +1174,9 @@ module API
         attributes.delete(:performance_bar_enabled)
         attributes.delete(:allow_local_requests_from_hooks_and_services)
 
+        # let's not expose the secret key in a response
+        attributes.delete(:asset_proxy_secret_key)
+
         attributes
       end
 
diff --git a/lib/api/settings.rb b/lib/api/settings.rb
index c36ee5af63f..b67c18b5465 100644
--- a/lib/api/settings.rb
+++ b/lib/api/settings.rb
@@ -36,6 +36,10 @@ module API
       given akismet_enabled: ->(val) { val } do
         requires :akismet_api_key, type: String, desc: 'Generate API key at http://www.akismet.com'
       end
+      optional :asset_proxy_enabled, type: Boolean, desc: 'Enable proxying of assets'
+      optional :asset_proxy_url, type: String, desc: 'URL of the asset proxy server'
+      optional :asset_proxy_secret_key, type: String, desc: 'Shared secret with the asset proxy server'
+      optional :asset_proxy_whitelist, type: Array[String], coerce_with: Validations::Types::CommaSeparatedToArray.coerce, desc: 'Assets that match these domain(s) will NOT be proxied. Wildcards allowed. Your GitLab installation URL is automatically whitelisted.'
       optional :container_registry_token_expire_delay, type: Integer, desc: 'Authorization token duration (minutes)'
       optional :default_artifacts_expire_in, type: String, desc: "Set the default expiration time for each job's artifacts"
       optional :default_project_creation, type: Integer, values: ::Gitlab::Access.project_creation_values, desc: 'Determine if developers can create projects in the group'
@@ -123,7 +127,7 @@ module API
       optional :terminal_max_session_time, type: Integer, desc: 'Maximum time for web terminal websocket connection (in seconds). Set to 0 for unlimited time.'
       optional :usage_ping_enabled, type: Boolean, desc: 'Every week GitLab will report license usage back to GitLab, Inc.'
       optional :instance_statistics_visibility_private, type: Boolean, desc: 'When set to `true` Instance statistics will only be available to admins'
-      optional :local_markdown_version, type: Integer, desc: "Local markdown version, increase this value when any cached markdown should be invalidated"
+      optional :local_markdown_version, type: Integer, desc: 'Local markdown version, increase this value when any cached markdown should be invalidated'
       optional :allow_local_requests_from_hooks_and_services, type: Boolean, desc: 'Deprecated: Use :allow_local_requests_from_web_hooks_and_services instead. Allow requests to the local network from hooks and services.' # support legacy names, can be removed in v5
       optional :snowplow_enabled, type: Grape::API::Boolean, desc: 'Enable Snowplow tracking'
       given snowplow_enabled: ->(val) { val } do
diff --git a/lib/api/validations/types/comma_separated_to_array.rb b/lib/api/validations/types/comma_separated_to_array.rb
new file mode 100644
index 00000000000..b551878abd1
--- /dev/null
+++ b/lib/api/validations/types/comma_separated_to_array.rb
@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+module API
+  module Validations
+    module Types
+      class CommaSeparatedToArray
+        def self.coerce
+          lambda do |value|
+            case value
+            when String
+              value.split(',').map(&:strip)
+            when Array
+              value.map { |v| v.to_s.split(',').map(&:strip) }.flatten
+            else
+              []
+            end
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/lib/banzai/filter/asset_proxy_filter.rb b/lib/banzai/filter/asset_proxy_filter.rb
new file mode 100644
index 00000000000..0a9a52a73a1
--- /dev/null
+++ b/lib/banzai/filter/asset_proxy_filter.rb
@@ -0,0 +1,62 @@
+# frozen_string_literal: true
+
+module Banzai
+  module Filter
+    # Proxy's images/assets to another server.  Reduces mixed content warnings
+    # as well as hiding the customer's IP address when requesting images.
+    # Copies the original img `src` to `data-canonical-src` then replaces the
+    # `src` with a new url to the proxy server.
+    class AssetProxyFilter < HTML::Pipeline::CamoFilter
+      def initialize(text, context = nil, result = nil)
+        super
+      end
+
+      def validate
+        needs(:asset_proxy, :asset_proxy_secret_key) if asset_proxy_enabled?
+      end
+
+      def asset_host_whitelisted?(host)
+        context[:asset_proxy_domain_regexp] ? context[:asset_proxy_domain_regexp].match?(host) : false
+      end
+
+      def self.transform_context(context)
+        context[:disable_asset_proxy] = !Gitlab.config.asset_proxy.enabled
+
+        unless context[:disable_asset_proxy]
+          context[:asset_proxy_enabled]       = !context[:disable_asset_proxy]
+          context[:asset_proxy]               = Gitlab.config.asset_proxy.url
+          context[:asset_proxy_secret_key]    = Gitlab.config.asset_proxy.secret_key
+          context[:asset_proxy_domain_regexp] = Gitlab.config.asset_proxy.domain_regexp
+        end
+
+        context
+      end
+
+      # called during an initializer. Caching the values in Gitlab.config significantly increased
+      # performance, rather than querying Gitlab::CurrentSettings.current_application_settings
+      # over and over.  However, this does mean that the Rails servers need to get restarted
+      # whenever the application settings are changed
+      def self.initialize_settings
+        application_settings           = Gitlab::CurrentSettings.current_application_settings
+        Gitlab.config['asset_proxy'] ||= Settingslogic.new({})
+
+        if application_settings.respond_to?(:asset_proxy_enabled)
+          Gitlab.config.asset_proxy['enabled']       = application_settings.asset_proxy_enabled
+          Gitlab.config.asset_proxy['url']           = application_settings.asset_proxy_url
+          Gitlab.config.asset_proxy['secret_key']    = application_settings.asset_proxy_secret_key
+          Gitlab.config.asset_proxy['whitelist']     = application_settings.asset_proxy_whitelist || [Gitlab.config.gitlab.host]
+          Gitlab.config.asset_proxy['domain_regexp'] = compile_whitelist(Gitlab.config.asset_proxy.whitelist)
+        else
+          Gitlab.config.asset_proxy['enabled']       = ::ApplicationSetting.defaults[:asset_proxy_enabled]
+        end
+      end
+
+      def self.compile_whitelist(domain_list)
+        return if domain_list.empty?
+
+        escaped = domain_list.map { |domain| Regexp.escape(domain).gsub('\*', '.*?') }
+        Regexp.new("^(#{escaped.join('|')})$", Regexp::IGNORECASE)
+      end
+    end
+  end
+end
diff --git a/lib/banzai/filter/external_link_filter.rb b/lib/banzai/filter/external_link_filter.rb
index 61ee3eac216..fb721fe12b1 100644
--- a/lib/banzai/filter/external_link_filter.rb
+++ b/lib/banzai/filter/external_link_filter.rb
@@ -14,10 +14,10 @@ module Banzai
           # such as on `mailto:` links. Since we've been using it, do an
           # initial parse for validity and then use Addressable
           # for IDN support, etc
-          uri = uri_strict(node['href'].to_s)
+          uri = uri_strict(node_src(node))
           if uri
-            node.set_attribute('href', uri.to_s)
-            addressable_uri = addressable_uri(node['href'])
+            node.set_attribute(node_src_attribute(node), uri.to_s)
+            addressable_uri = addressable_uri(node_src(node))
           else
             addressable_uri = nil
           end
@@ -35,6 +35,16 @@ module Banzai
 
       private
 
+      # if this is a link to a proxied image, then `src` is already the correct
+      # proxied url, so work with the `data-canonical-src`
+      def node_src_attribute(node)
+        node['data-canonical-src'] ? 'data-canonical-src' : 'href'
+      end
+
+      def node_src(node)
+        node[node_src_attribute(node)]
+      end
+
       def uri_strict(href)
         URI.parse(href)
       rescue URI::Error
@@ -72,7 +82,7 @@ module Banzai
         return unless uri
         return unless context[:emailable_links]
 
-        unencoded_uri_str = Addressable::URI.unencode(node['href'])
+        unencoded_uri_str = Addressable::URI.unencode(node_src(node))
 
         if unencoded_uri_str == node.content && idn?(uri)
           node.content = uri.normalize
diff --git a/lib/banzai/filter/image_link_filter.rb b/lib/banzai/filter/image_link_filter.rb
index 01237303c27..ed0a01e6277 100644
--- a/lib/banzai/filter/image_link_filter.rb
+++ b/lib/banzai/filter/image_link_filter.rb
@@ -18,6 +18,9 @@ module Banzai
             rel: 'noopener noreferrer'
           )
 
+          # make sure the original non-proxied src carries over to the link
+          link['data-canonical-src'] = img['data-canonical-src'] if img['data-canonical-src']
+
           link.children = img.clone
 
           img.replace(link)
diff --git a/lib/banzai/filter/video_link_filter.rb b/lib/banzai/filter/video_link_filter.rb
index 0fff104cf91..a278fcfdb47 100644
--- a/lib/banzai/filter/video_link_filter.rb
+++ b/lib/banzai/filter/video_link_filter.rb
@@ -23,6 +23,14 @@ module Banzai
             "'.#{ext}' = substring(@src, string-length(@src) - #{ext.size})"
           end
 
+          if context[:asset_proxy_enabled].present?
+            src_query.concat(
+              UploaderHelper::VIDEO_EXT.map do |ext|
+                "'.#{ext}' = substring(@data-canonical-src, string-length(@data-canonical-src) - #{ext.size})"
+              end
+            )
+          end
+
           "descendant-or-self::img[not(ancestor::a) and (#{src_query.join(' or ')})]"
         end
       end
@@ -48,6 +56,13 @@ module Banzai
           target: '_blank',
           rel: 'noopener noreferrer',
           title: "Download '#{element['title'] || element['alt']}'")
+
+        # make sure the original non-proxied src carries over
+        if element['data-canonical-src']
+          video['data-canonical-src'] = element['data-canonical-src']
+          link['data-canonical-src']  = element['data-canonical-src']
+        end
+
         download_paragraph = doc.document.create_element('p')
         download_paragraph.children = link
 
diff --git a/lib/banzai/pipeline/ascii_doc_pipeline.rb b/lib/banzai/pipeline/ascii_doc_pipeline.rb
index d25b74b23b2..82b99d3de4a 100644
--- a/lib/banzai/pipeline/ascii_doc_pipeline.rb
+++ b/lib/banzai/pipeline/ascii_doc_pipeline.rb
@@ -6,12 +6,17 @@ module Banzai
       def self.filters
         FilterArray[
           Filter::AsciiDocSanitizationFilter,
+          Filter::AssetProxyFilter,
           Filter::SyntaxHighlightFilter,
           Filter::ExternalLinkFilter,
           Filter::PlantumlFilter,
           Filter::AsciiDocPostProcessingFilter
         ]
       end
+
+      def self.transform_context(context)
+        Filter::AssetProxyFilter.transform_context(context)
+      end
     end
   end
 end
diff --git a/lib/banzai/pipeline/gfm_pipeline.rb b/lib/banzai/pipeline/gfm_pipeline.rb
index 2c1006f708a..f419e54c264 100644
--- a/lib/banzai/pipeline/gfm_pipeline.rb
+++ b/lib/banzai/pipeline/gfm_pipeline.rb
@@ -17,6 +17,7 @@ module Banzai
           Filter::SpacedLinkFilter,
 
           Filter::SanitizationFilter,
+          Filter::AssetProxyFilter,
           Filter::SyntaxHighlightFilter,
 
           Filter::MathFilter,
@@ -60,7 +61,7 @@ module Banzai
       def self.transform_context(context)
         context[:only_path] = true unless context.key?(:only_path)
 
-        context
+        Filter::AssetProxyFilter.transform_context(context)
       end
     end
   end
diff --git a/lib/banzai/pipeline/markup_pipeline.rb b/lib/banzai/pipeline/markup_pipeline.rb
index ceba082cd4f..c86d5f08ded 100644
--- a/lib/banzai/pipeline/markup_pipeline.rb
+++ b/lib/banzai/pipeline/markup_pipeline.rb
@@ -6,11 +6,16 @@ module Banzai
       def self.filters
         @filters ||= FilterArray[
           Filter::SanitizationFilter,
+          Filter::AssetProxyFilter,
           Filter::ExternalLinkFilter,
           Filter::PlantumlFilter,
           Filter::SyntaxHighlightFilter
         ]
       end
+
+      def self.transform_context(context)
+        Filter::AssetProxyFilter.transform_context(context)
+      end
     end
   end
 end
diff --git a/lib/banzai/pipeline/single_line_pipeline.rb b/lib/banzai/pipeline/single_line_pipeline.rb
index 72374207a8f..9aff6880f56 100644
--- a/lib/banzai/pipeline/single_line_pipeline.rb
+++ b/lib/banzai/pipeline/single_line_pipeline.rb
@@ -7,6 +7,7 @@ module Banzai
         @filters ||= FilterArray[
           Filter::HtmlEntityFilter,
           Filter::SanitizationFilter,
+          Filter::AssetProxyFilter,
 
           Filter::EmojiFilter,
           Filter::AutolinkFilter,
@@ -29,6 +30,8 @@ module Banzai
       end
 
       def self.transform_context(context)
+        context = Filter::AssetProxyFilter.transform_context(context)
+
         super(context).merge(
           no_sourcepos: true
         )
diff --git a/spec/initializers/asset_proxy_setting_spec.rb b/spec/initializers/asset_proxy_setting_spec.rb
new file mode 100644
index 00000000000..42e4d4aa594
--- /dev/null
+++ b/spec/initializers/asset_proxy_setting_spec.rb
@@ -0,0 +1,13 @@
+require 'spec_helper'
+
+describe 'Asset proxy settings initialization' do
+  describe '#asset_proxy' do
+    it 'defaults to disabled' do
+      expect(Banzai::Filter::AssetProxyFilter).to receive(:initialize_settings)
+
+      require_relative '../../config/initializers/asset_proxy_settings'
+
+      expect(Gitlab.config.asset_proxy.enabled).to be_falsey
+    end
+  end
+end
diff --git a/spec/lib/banzai/filter/asset_proxy_filter_spec.rb b/spec/lib/banzai/filter/asset_proxy_filter_spec.rb
new file mode 100644
index 00000000000..b7f45421b2a
--- /dev/null
+++ b/spec/lib/banzai/filter/asset_proxy_filter_spec.rb
@@ -0,0 +1,95 @@
+require 'spec_helper'
+
+describe Banzai::Filter::AssetProxyFilter do
+  include FilterSpecHelper
+
+  def image(path)
+    %(<img src="#{path}" />)
+  end
+
+  it 'does not replace if disabled' do
+    stub_asset_proxy_setting(enabled: false)
+
+    context = described_class.transform_context({})
+    src     = 'http://example.com/test.png'
+    doc     = filter(image(src), context)
+
+    expect(doc.at_css('img')['src']).to eq src
+  end
+
+  context 'during initialization' do
+    after do
+      Gitlab.config.asset_proxy['enabled'] = false
+    end
+
+    it '#initialize_settings' do
+      stub_application_setting(asset_proxy_enabled: true)
+      stub_application_setting(asset_proxy_secret_key: 'shared-secret')
+      stub_application_setting(asset_proxy_url: 'https://assets.example.com')
+      stub_application_setting(asset_proxy_whitelist: %w(gitlab.com *.mydomain.com))
+
+      described_class.initialize_settings
+
+      expect(Gitlab.config.asset_proxy.enabled).to be_truthy
+      expect(Gitlab.config.asset_proxy.secret_key).to eq 'shared-secret'
+      expect(Gitlab.config.asset_proxy.url).to eq 'https://assets.example.com'
+      expect(Gitlab.config.asset_proxy.whitelist).to eq %w(gitlab.com *.mydomain.com)
+      expect(Gitlab.config.asset_proxy.domain_regexp).to eq /^(gitlab\.com|.*?\.mydomain\.com)$/i
+    end
+  end
+
+  context 'when properly configured' do
+    before do
+      stub_asset_proxy_setting(enabled: true)
+      stub_asset_proxy_setting(secret_key: 'shared-secret')
+      stub_asset_proxy_setting(url: 'https://assets.example.com')
+      stub_asset_proxy_setting(whitelist: %W(gitlab.com *.mydomain.com #{Gitlab.config.gitlab.host}))
+      stub_asset_proxy_setting(domain_regexp: described_class.compile_whitelist(Gitlab.config.asset_proxy.whitelist))
+      @context = described_class.transform_context({})
+    end
+
+    it 'replaces img src' do
+      src     = 'http://example.com/test.png'
+      new_src = 'https://assets.example.com/08df250eeeef1a8cf2c761475ac74c5065105612/687474703a2f2f6578616d706c652e636f6d2f746573742e706e67'
+      doc     = filter(image(src), @context)
+
+      expect(doc.at_css('img')['src']).to eq new_src
+      expect(doc.at_css('img')['data-canonical-src']).to eq src
+    end
+
+    it 'skips internal images' do
+      src      = "#{Gitlab.config.gitlab.url}/test.png"
+      doc      = filter(image(src), @context)
+
+      expect(doc.at_css('img')['src']).to eq src
+    end
+
+    it 'skip relative urls' do
+      src = "/test.png"
+      doc = filter(image(src), @context)
+
+      expect(doc.at_css('img')['src']).to eq src
+    end
+
+    it 'skips single domain' do
+      src = "http://gitlab.com/test.png"
+      doc = filter(image(src), @context)
+
+      expect(doc.at_css('img')['src']).to eq src
+    end
+
+    it 'skips single domain and ignores url in query string' do
+      src = "http://gitlab.com/test.png?url=http://example.com/test.png"
+      doc = filter(image(src), @context)
+
+      expect(doc.at_css('img')['src']).to eq src
+    end
+
+    it 'skips wildcarded domain' do
+      src = "http://images.mydomain.com/test.png"
+      doc = filter(image(src), @context)
+
+      expect(doc.at_css('img')['src']).to eq src
+    end
+  end
+end
diff --git a/spec/lib/banzai/filter/external_link_filter_spec.rb b/spec/lib/banzai/filter/external_link_filter_spec.rb
index 59fea5766ee..4b2500b31f7 100644
--- a/spec/lib/banzai/filter/external_link_filter_spec.rb
+++ b/spec/lib/banzai/filter/external_link_filter_spec.rb
@@ -156,6 +156,18 @@ describe Banzai::Filter::ExternalLinkFilter do
         expect(doc_email.to_html).to include('http://xn--example-6p25f.com/</a>')
       end
     end
+
+    context 'autolinked image' do
+      let(:html) { %q(<a href="https://assets.example.com/6d8b/634c" data-canonical-src="http://exa%F0%9F%98%84mple.com/test.png"><img src="http://exa%F0%9F%98%84mple.com/test.png" data-canonical-src="http://exa%F0%9F%98%84mple.com/test.png"></a>) }
+      let(:doc)  { filter(html) }
+
+      it_behaves_like 'an external link with rel attribute'
+
+      it 'adds a toolip with punycode' do
+        expect(doc.to_html).to include('class="has-tooltip"')
+        expect(doc.to_html).to include('title="http://xn--example-6p25f.com/test.png"')
+      end
+    end
   end
 
   context 'for links that look malicious' do
diff --git a/spec/lib/banzai/filter/image_link_filter_spec.rb b/spec/lib/banzai/filter/image_link_filter_spec.rb
index 7b0cb675551..011e3a1e2da 100644
--- a/spec/lib/banzai/filter/image_link_filter_spec.rb
+++ b/spec/lib/banzai/filter/image_link_filter_spec.rb
@@ -28,4 +28,11 @@ describe Banzai::Filter::ImageLinkFilter do
     doc = filter(%Q(<p>test #{image('/uploads/e90decf88d8f96fe9e1389afc2e4a91f/test.jpg')} inline</p>))
     expect(doc.to_html).to match %r{^<p>test <a[^>]*><img[^>]*></a> inline</p>$}
   end
+
+  it 'keep the data-canonical-src' do
+    doc = filter(%q(<img src="http://assets.example.com/6cd/4d7" data-canonical-src="http://example.com/test.png" />))
+
+    expect(doc.at_css('img')['src']).to eq doc.at_css('a')['href']
+    expect(doc.at_css('img')['data-canonical-src']).to eq doc.at_css('a')['data-canonical-src']
+  end
 end
diff --git a/spec/lib/banzai/filter/video_link_filter_spec.rb b/spec/lib/banzai/filter/video_link_filter_spec.rb
index 483e806624c..cd932f502f3 100644
--- a/spec/lib/banzai/filter/video_link_filter_spec.rb
+++ b/spec/lib/banzai/filter/video_link_filter_spec.rb
@@ -49,4 +49,26 @@ describe Banzai::Filter::VideoLinkFilter do
       expect(element['src']).to eq '/path/my_image.jpg'
     end
   end
+
+  context 'when asset proxy is enabled' do
+    it 'uses the correct src' do
+      stub_asset_proxy_setting(enabled: true)
+
+      proxy_src = 'https://assets.example.com/6d8b63'
+      canonical_src = 'http://example.com/test.mp4'
+      image = %(<img src="#{proxy_src}" data-canonical-src="#{canonical_src}" />)
+      container = filter(image, asset_proxy_enabled: true).children.first
+
+      expect(container['class']).to eq 'video-container'
+
+      video, paragraph = container.children
+
+      expect(video['src']).to eq proxy_src
+      expect(video['data-canonical-src']).to eq canonical_src
+
+      link = paragraph.children.first
+
+      expect(link['href']).to eq proxy_src
+    end
+  end
 end
diff --git a/spec/lib/banzai/pipeline/gfm_pipeline_spec.rb b/spec/lib/banzai/pipeline/gfm_pipeline_spec.rb
index 0a3e0962452..3a9ecd2fb81 100644
--- a/spec/lib/banzai/pipeline/gfm_pipeline_spec.rb
+++ b/spec/lib/banzai/pipeline/gfm_pipeline_spec.rb
@@ -142,4 +142,48 @@ describe Banzai::Pipeline::GfmPipeline do
       expect(output).to include(Gitlab::Routing.url_helpers.milestone_path(milestone))
     end
   end
+
+  describe 'asset proxy' do
+    let(:project) { create(:project, :public) }
+    let(:image)   { '![proxy](http://example.com/test.png)' }
+    let(:proxy)   { 'https://assets.example.com/08df250eeeef1a8cf2c761475ac74c5065105612/687474703a2f2f6578616d706c652e636f6d2f746573742e706e67' }
+    let(:version) { Gitlab::CurrentSettings.current_application_settings.local_markdown_version }
+
+    before do
+      stub_asset_proxy_setting(enabled: true)
+      stub_asset_proxy_setting(secret_key: 'shared-secret')
+      stub_asset_proxy_setting(url: 'https://assets.example.com')
+      stub_asset_proxy_setting(whitelist: %W(gitlab.com *.mydomain.com #{Gitlab.config.gitlab.host}))
+      stub_asset_proxy_setting(domain_regexp: Banzai::Filter::AssetProxyFilter.compile_whitelist(Gitlab.config.asset_proxy.whitelist))
+    end
+
+    it 'replaces a lazy loaded img src' do
+      output = described_class.to_html(image, project: project)
+      doc    = Nokogiri::HTML.fragment(output)
+      result = doc.css('img').first
+
+      expect(result['data-src']).to eq(proxy)
+    end
+
+    it 'autolinks images to the proxy' do
+      output = described_class.to_html(image, project: project)
+      doc    = Nokogiri::HTML.fragment(output)
+      result = doc.css('a').first
+
+      expect(result['href']).to eq(proxy)
+      expect(result['data-canonical-src']).to eq('http://example.com/test.png')
+    end
+
+    it 'properly adds tooltips to link for IDN images' do
+      image  = '![proxy](http://exa😄mple.com/test.png)'
+      proxy  = 'https://assets.example.com/6d8b634c412a23c6bfe1b2963f174febf5635ddd/687474703a2f2f6578612546302539462539382538346d706c652e636f6d2f746573742e706e67'
+      output = described_class.to_html(image, project: project)
+      doc    = Nokogiri::HTML.fragment(output)
+      result = doc.css('a').first
+
+      expect(result['href']).to eq(proxy)
+      expect(result['data-canonical-src']).to eq('http://exa%F0%9F%98%84mple.com/test.png')
+      expect(result['title']).to eq 'http://xn--example-6p25f.com/test.png'
+    end
+  end
 end
diff --git a/spec/models/application_setting_spec.rb b/spec/models/application_setting_spec.rb
index db80b85360f..4f7a6d102b8 100644
--- a/spec/models/application_setting_spec.rb
+++ b/spec/models/application_setting_spec.rb
@@ -355,6 +355,71 @@ describe ApplicationSetting do
         end
       end
     end
+
+    context 'asset proxy settings' do
+      before do
+        subject.asset_proxy_enabled = true
+      end
+
+      describe '#asset_proxy_url' do
+        it { is_expected.not_to allow_value('').for(:asset_proxy_url) }
+        it { is_expected.to allow_value(http).for(:asset_proxy_url) }
+        it { is_expected.to allow_value(https).for(:asset_proxy_url) }
+        it { is_expected.not_to allow_value(ftp).for(:asset_proxy_url) }
+
+        it 'is not required when asset proxy is disabled' do
+          subject.asset_proxy_enabled = false
+          subject.asset_proxy_url = ''
+
+          expect(subject).to be_valid
+        end
+      end
+
+      describe '#asset_proxy_secret_key' do
+        it { is_expected.not_to allow_value('').for(:asset_proxy_secret_key) }
+        it { is_expected.to allow_value('anything').for(:asset_proxy_secret_key) }
+
+        it 'is not required when asset proxy is disabled' do
+          subject.asset_proxy_enabled = false
+          subject.asset_proxy_secret_key = ''
+
+          expect(subject).to be_valid
+        end
+
+        it 'is encrypted' do
+          subject.asset_proxy_secret_key = 'shared secret'
+
+          expect(subject.encrypted_asset_proxy_secret_key).to be_present
+          expect(subject.encrypted_asset_proxy_secret_key).not_to eq(subject.asset_proxy_secret_key)
+        end
+      end
+
+      describe '#asset_proxy_whitelist' do
+        context 'when given an Array' do
+          it 'sets the domains and adds current running host' do
+            setting.asset_proxy_whitelist = ['example.com', 'assets.example.com']
+            expect(setting.asset_proxy_whitelist).to eq(['example.com', 'assets.example.com', 'localhost'])
+          end
+        end
+
+        context 'when given a String' do
+          it 'sets multiple domains with spaces' do
+            setting.asset_proxy_whitelist = 'example.com *.example.com'
+            expect(setting.asset_proxy_whitelist).to eq(['example.com', '*.example.com', 'localhost'])
+          end
+
+          it 'sets multiple domains with newlines and a space' do
+            setting.asset_proxy_whitelist = "example.com\n *.example.com"
+            expect(setting.asset_proxy_whitelist).to eq(['example.com', '*.example.com', 'localhost'])
+          end
+
+          it 'sets multiple domains with commas' do
+            setting.asset_proxy_whitelist = "example.com, *.example.com"
+            expect(setting.asset_proxy_whitelist).to eq(['example.com', '*.example.com', 'localhost'])
+          end
+        end
+      end
+    end
   end
 
   context 'restrict creating duplicates' do
diff --git a/spec/requests/api/settings_spec.rb b/spec/requests/api/settings_spec.rb
index 590107d5161..048d04cdefd 100644
--- a/spec/requests/api/settings_spec.rb
+++ b/spec/requests/api/settings_spec.rb
@@ -224,5 +224,33 @@ describe API::Settings, 'Settings' do
         expect(json_response['error']).to eq('plantuml_url is missing')
       end
     end
+
+    context 'asset_proxy settings' do
+      it 'updates application settings' do
+        put api('/application/settings', admin),
+          params: {
+            asset_proxy_enabled: true,
+            asset_proxy_url: 'http://assets.example.com',
+            asset_proxy_secret_key: 'shared secret',
+            asset_proxy_whitelist: ['example.com', '*.example.com']
+          }
+
+        expect(response).to have_gitlab_http_status(200)
+        expect(json_response['asset_proxy_enabled']).to be(true)
+        expect(json_response['asset_proxy_url']).to eq('http://assets.example.com')
+        expect(json_response['asset_proxy_secret_key']).to be_nil
+        expect(json_response['asset_proxy_whitelist']).to eq(['example.com', '*.example.com', 'localhost'])
+      end
+
+      it 'allows a string for asset_proxy_whitelist' do
+        put api('/application/settings', admin),
+          params: {
+            asset_proxy_whitelist: 'example.com, *.example.com'
+          }
+
+        expect(response).to have_gitlab_http_status(200)
+        expect(json_response['asset_proxy_whitelist']).to eq(['example.com', '*.example.com', 'localhost'])
+      end
+    end
   end
 end
diff --git a/spec/services/application_settings/update_service_spec.rb b/spec/services/application_settings/update_service_spec.rb
index adb5219d691..74f94f8ed0f 100644
--- a/spec/services/application_settings/update_service_spec.rb
+++ b/spec/services/application_settings/update_service_spec.rb
@@ -110,6 +110,39 @@ describe ApplicationSettings::UpdateService do
     end
   end
 
+  describe 'markdown cache invalidators' do
+    shared_examples 'invalidates markdown cache' do |attribute|
+      let(:params) { attribute }
+
+      it 'increments cache' do
+        expect { subject.execute }.to change(application_settings, :local_markdown_version).by(1)
+      end
+    end
+
+    it_behaves_like 'invalidates markdown cache', { asset_proxy_enabled: true }
+    it_behaves_like 'invalidates markdown cache', { asset_proxy_url: 'http://test.com' }
+    it_behaves_like 'invalidates markdown cache', { asset_proxy_secret_key: 'another secret' }
+    it_behaves_like 'invalidates markdown cache', { asset_proxy_whitelist: ['domain.com'] }
+
+    context 'when also setting the local_markdown_version' do
+      let(:params) { { asset_proxy_enabled: true, local_markdown_version: 12 } }
+
+      it 'does not increment' do
+        expect { subject.execute }.to change(application_settings, :local_markdown_version).to(12)
+      end
+    end
+
+    context 'do not invalidate if value does not change' do
+      let(:params) { { asset_proxy_enabled: true, asset_proxy_secret_key: 'secret', asset_proxy_url: 'http://test.com' } }
+
+      it 'does not increment' do
+        described_class.new(application_settings, admin, params).execute
+
+        expect { described_class.new(application_settings, admin, params).execute }.not_to change(application_settings, :local_markdown_version)
+      end
+    end
+  end
+
   describe 'performance bar settings' do
     using RSpec::Parameterized::TableSyntax
 
diff --git a/spec/support/helpers/stub_configuration.rb b/spec/support/helpers/stub_configuration.rb
index dec7898d8d2..f364e4fd158 100644
--- a/spec/support/helpers/stub_configuration.rb
+++ b/spec/support/helpers/stub_configuration.rb
@@ -105,6 +105,10 @@ module StubConfiguration
     allow(Gitlab.config.gitlab_shell).to receive_messages(to_settings(messages))
   end
 
+  def stub_asset_proxy_setting(messages)
+    allow(Gitlab.config.asset_proxy).to receive_messages(to_settings(messages))
+  end
+
   def stub_rack_attack_setting(messages)
     allow(Gitlab.config.rack_attack).to receive(:git_basic_auth).and_return(messages)
     allow(Gitlab.config.rack_attack.git_basic_auth).to receive_messages(to_settings(messages))