diff --git a/CHANGELOG.md b/CHANGELOG.md
index a53790afafb8d1..c9b24d6f159e31 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,61 @@
 
 All notable changes to this project will be documented in this file.
 
+## [4.2.9] - 2024-05-30
+
+### Security
+
+- Update dependencies
+- Fix private mention filtering ([GHSA-5fq7-3p3j-9vrf](https://github.com/mastodon/mastodon/security/advisories/GHSA-5fq7-3p3j-9vrf))
+- Fix password change endpoint not being rate-limited ([GHSA-q3rg-xx5v-4mxh](https://github.com/mastodon/mastodon/security/advisories/GHSA-q3rg-xx5v-4mxh))
+- Add hardening around rate-limit bypass ([GHSA-c2r5-cfqr-c553](https://github.com/mastodon/mastodon/security/advisories/GHSA-c2r5-cfqr-c553))
+
+### Added
+
+- Add rate-limit on OAuth application registration ([ThisIsMissEm](https://github.com/mastodon/mastodon/pull/30316))
+- Add fallback redirection when getting a webfinger query `WEB_DOMAIN@WEB_DOMAIN` ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/28592))
+- Add `digest` attribute to `Admin::DomainBlock` entity in REST API ([ThisIsMissEm](https://github.com/mastodon/mastodon/pull/29092))
+
+### Removed
+
+- Remove superfluous application-level caching in some controllers ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/29862))
+- Remove aggressive OAuth application vacuuming ([ThisIsMissEm](https://github.com/mastodon/mastodon/pull/30316))
+
+### Fixed
+
+- Fix leaking Elasticsearch connections in Sidekiq processes ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/30450))
+- Fix language of remote posts not being recognized when using unusual casing ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/30403))
+- Fix off-by-one in `tootctl media` commands ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/30306))
+- Fix removal of allowed domains (in `LIMITED_FEDERATION_MODE`) not being recorded in the audit log ([ThisIsMissEm](https://github.com/mastodon/mastodon/pull/30125))
+- Fix not being able to block a subdomain of an already-blocked domain through the API ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/30119))
+- Fix `Idempotency-Key` being ignored when scheduling a post ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/30084))
+- Fix crash when supplying the `FFMPEG_BINARY` environment variable ([timothyjrogers](https://github.com/mastodon/mastodon/pull/30022))
+- Fix improper email address validation ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/29838))
+- Fix results/query in `api/v1/featured_tags/suggestions` ([mjankowski](https://github.com/mastodon/mastodon/pull/29597))
+- Fix unblocking internationalized domain names under certain conditions ([tribela](https://github.com/mastodon/mastodon/pull/29530))
+- Fix admin account created by `mastodon:setup` not being auto-approved ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/29379))
+- Fix reference to non-existent var in CLI maintenance command ([mjankowski](https://github.com/mastodon/mastodon/pull/28363))
+
+## [4.2.8] - 2024-02-23
+
+### Added
+
+- Add hourly task to automatically require approval for new registrations in the absence of moderators ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/29318), [ClearlyClaire](https://github.com/mastodon/mastodon/pull/29355))
+  In order to prevent future abandoned Mastodon servers from being used for spam, harassment and other malicious activity, Mastodon will now automatically switch new user registrations to require moderator approval whenever they are left open and no activity (including non-moderation actions from apps) from any logged-in user with permission to access moderation reports has been detected in a full week.
+  When this happens, users with the permission to change server settings will receive an email notification.
+  This feature is disabled when `EMAIL_DOMAIN_ALLOWLIST` is used, and can also be disabled with `DISABLE_AUTOMATIC_SWITCHING_TO_APPROVED_REGISTRATIONS=true`.
+
+### Changed
+
+- Change registrations to be closed by default on new installations ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/29280))
+  If you are running a server and never changed your registrations mode from the default, updating will automatically close your registrations.
+  Simply re-enable them through the administration interface or using `tootctl settings registrations open` if you want to enable them again.
+
+### Fixed
+
+- Fix processing of remote ActivityPub actors making use of `Link` objects as `Image` `url` ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/29335))
+- Fix link verifications when page size exceeds 1MB ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/29358))
+
 ## [4.2.7] - 2024-02-16
 
 ### Fixed
diff --git a/app/services/notify_service.rb b/app/services/notify_service.rb
index e56562c0a59c58..1f01c2d48e0425 100644
--- a/app/services/notify_service.rb
+++ b/app/services/notify_service.rb
@@ -147,6 +147,9 @@ def response_to_recipient?
     end
 
     def statuses_that_mention_sender
+      # This queries private mentions from the recipient to the sender up in the thread.
+      # This allows up to 100 messages that do not match in the thread, allowing conversations
+      # involving multiple people.
       Status.count_by_sql([<<-SQL.squish, id: @notification.target_status.in_reply_to_id, recipient_id: @recipient.id, sender_id: @sender.id, depth_limit: 100])
         WITH RECURSIVE ancestors(id, in_reply_to_id, mention_id, path, depth) AS (
             SELECT s.id, s.in_reply_to_id, m.id, ARRAY[s.id], 0
@@ -154,16 +157,17 @@ def statuses_that_mention_sender
             LEFT JOIN mentions m ON m.silent = FALSE AND m.account_id = :sender_id AND m.status_id = s.id
             WHERE s.id = :id
           UNION ALL
-            SELECT s.id, s.in_reply_to_id, m.id, st.path || s.id, st.depth + 1
-            FROM ancestors st
-            JOIN statuses s ON s.id = st.in_reply_to_id
-            LEFT JOIN mentions m ON m.silent = FALSE AND m.account_id = :sender_id AND m.status_id = s.id
-            WHERE st.mention_id IS NULL AND NOT s.id = ANY(path) AND st.depth < :depth_limit
+            SELECT s.id, s.in_reply_to_id, m.id, ancestors.path || s.id, ancestors.depth + 1
+            FROM ancestors
+            JOIN statuses s ON s.id = ancestors.in_reply_to_id
+            /* early exit if we already have a mention matching our requirements */
+            LEFT JOIN mentions m ON m.silent = FALSE AND m.account_id = :sender_id AND m.status_id = s.id AND s.account_id = :recipient_id
+            WHERE ancestors.mention_id IS NULL AND NOT s.id = ANY(path) AND ancestors.depth < :depth_limit
         )
         SELECT COUNT(*)
-        FROM ancestors st
-        JOIN statuses s ON s.id = st.id
-        WHERE st.mention_id IS NOT NULL AND s.visibility = 3
+        FROM ancestors
+        JOIN statuses s ON s.id = ancestors.id
+        WHERE ancestors.mention_id IS NOT NULL AND s.account_id = :recipient_id AND s.visibility = 3
       SQL
     end
   end
diff --git a/config/application.rb b/config/application.rb
index 07b50ca036ba99..6d6e91a5cc7dfe 100644
--- a/config/application.rb
+++ b/config/application.rb
@@ -48,6 +48,7 @@
 require_relative '../lib/webpacker/manifest_extensions'
 require_relative '../lib/webpacker/helper_extensions'
 require_relative '../lib/rails/engine_extensions'
+require_relative '../lib/action_dispatch/remote_ip_extensions'
 require_relative '../lib/active_record/database_tasks_extensions'
 require_relative '../lib/active_record/batches'
 require_relative '../lib/simple_navigation/item_extensions'
diff --git a/config/initializers/rack_attack.rb b/config/initializers/rack_attack.rb
index 1757ce5df1e487..14fab7ecda170e 100644
--- a/config/initializers/rack_attack.rb
+++ b/config/initializers/rack_attack.rb
@@ -37,6 +37,10 @@ def authenticated_token_id
       authenticated_token&.id
     end
 
+    def warden_user_id
+      @env['warden']&.user&.id
+    end
+
     def unauthenticated?
       !authenticated_user_id
     end
@@ -58,10 +62,6 @@ def paging_request?
     end
   end
 
-  Rack::Attack.safelist('allow from localhost') do |req|
-    req.remote_ip == '127.0.0.1' || req.remote_ip == '::1'
-  end
-
   Rack::Attack.blocklist('deny from blocklist') do |req|
     IpBlock.blocked?(req.remote_ip)
   end
@@ -141,6 +141,10 @@ def paging_request?
     req.session[:attempt_user_id] || req.params.dig('user', 'email').presence if req.post? && req.path_matches?('/auth/sign_in')
   end
 
+  throttle('throttle_password_change/account', limit: 10, period: 10.minutes) do |req|
+    req.warden_user_id if req.put? || (req.patch? && req.path_matches?('/auth'))
+  end
+
   self.throttled_responder = lambda do |request|
     now        = Time.now.utc
     match_data = request.env['rack.attack.match_data']
diff --git a/docker-compose.yml b/docker-compose.yml
index 3f2336f1d96241..e7ae95ea7aa71a 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -55,7 +55,7 @@ services:
 
   web:
     build: .
-    image: ghcr.io/mastodon/mastodon:v4.2.7
+    image: ghcr.io/mastodon/mastodon:v4.2.9
     restart: always
     env_file: .env.production
     command: bundle exec puma -C config/puma.rb
@@ -76,7 +76,7 @@ services:
 
   streaming:
     build: .
-    image: ghcr.io/mastodon/mastodon:v4.2.7
+    image: ghcr.io/mastodon/mastodon:v4.2.9
     restart: always
     env_file: .env.production
     command: node ./streaming
@@ -94,7 +94,7 @@ services:
 
   sidekiq:
     build: .
-    image: ghcr.io/mastodon/mastodon:v4.2.7
+    image: ghcr.io/mastodon/mastodon:v4.2.9
     restart: always
     env_file: .env.production
     command: bundle exec sidekiq
diff --git a/lib/action_dispatch/remote_ip_extensions.rb b/lib/action_dispatch/remote_ip_extensions.rb
new file mode 100644
index 00000000000000..e5c48bf3c5b0ee
--- /dev/null
+++ b/lib/action_dispatch/remote_ip_extensions.rb
@@ -0,0 +1,72 @@
+# frozen_string_literal: true
+
+# Mastodon is not made to be directly accessed without a reverse proxy.
+# This monkey-patch prevents remote IP address spoofing when being accessed
+# directly.
+#
+# See PR: https://github.com/rails/rails/pull/51610
+
+# In addition to the PR above, it also raises an error if a request with
+# `X-Forwarded-For` or `Client-Ip` comes directly from a client without
+# going through a trusted proxy.
+
+# rubocop:disable all -- This is a mostly vendored file
+
+module ActionDispatch
+  class RemoteIp
+    module GetIpExtensions
+      def calculate_ip
+        # Set by the Rack web server, this is a single value.
+        remote_addr = ips_from(@req.remote_addr).last
+
+        # Could be a CSV list and/or repeated headers that were concatenated.
+        client_ips    = ips_from(@req.client_ip).reverse!
+        forwarded_ips = ips_from(@req.x_forwarded_for).reverse!
+
+        # `Client-Ip` and `X-Forwarded-For` should not, generally, both be set. If they
+        # are both set, it means that either:
+        #
+        # 1) This request passed through two proxies with incompatible IP header
+        #     conventions.
+        #
+        # 2) The client passed one of `Client-Ip` or `X-Forwarded-For`
+        #     (whichever the proxy servers weren't using) themselves.
+        #
+        # Either way, there is no way for us to determine which header is the right one
+        # after the fact. Since we have no idea, if we are concerned about IP spoofing
+        # we need to give up and explode. (If you're not concerned about IP spoofing you
+        # can turn the `ip_spoofing_check` option off.)
+        should_check_ip = @check_ip && client_ips.last && forwarded_ips.last
+        if should_check_ip && !forwarded_ips.include?(client_ips.last)
+          # We don't know which came from the proxy, and which from the user
+          raise IpSpoofAttackError, "IP spoofing attack?! " \
+            "HTTP_CLIENT_IP=#{@req.client_ip.inspect} " \
+            "HTTP_X_FORWARDED_FOR=#{@req.x_forwarded_for.inspect}"
+        end
+
+        # NOTE: Mastodon addition to make sure we don't get requests from a non-trusted client
+        if @check_ip && (forwarded_ips.last || client_ips.last) && !@proxies.any? { |proxy| proxy === remote_addr }
+          raise IpSpoofAttackError, "IP spoofing attack?! client #{remote_addr} is not a trusted proxy " \
+            "HTTP_CLIENT_IP=#{@req.client_ip.inspect} " \
+            "HTTP_X_FORWARDED_FOR=#{@req.x_forwarded_for.inspect}"
+        end
+
+        # We assume these things about the IP headers:
+        #
+        #     - X-Forwarded-For will be a list of IPs, one per proxy, or blank
+        #     - Client-Ip is propagated from the outermost proxy, or is blank
+        #     - REMOTE_ADDR will be the IP that made the request to Rack
+        ips = forwarded_ips + client_ips
+        ips.compact!
+
+        # If every single IP option is in the trusted list, return the IP that's
+        # furthest away
+        filter_proxies([remote_addr] + ips).first || ips.last || remote_addr
+      end
+    end
+  end
+end
+
+ActionDispatch::RemoteIp::GetIp.prepend(ActionDispatch::RemoteIp::GetIpExtensions)
+
+# rubocop:enable all
diff --git a/lib/mastodon/version.rb b/lib/mastodon/version.rb
index 5d7f3d4d0c3f20..b48560921e5561 100644
--- a/lib/mastodon/version.rb
+++ b/lib/mastodon/version.rb
@@ -17,7 +17,7 @@ def patch
     end
 
     def default_prerelease
-      'alpha.3'
+      'alpha.4'
     end
 
     def prerelease
diff --git a/spec/config/initializers/rack/attack_spec.rb b/spec/config/initializers/rack/attack_spec.rb
index 0a388c2f411d7b..19de4808983bc9 100644
--- a/spec/config/initializers/rack/attack_spec.rb
+++ b/spec/config/initializers/rack/attack_spec.rb
@@ -56,7 +56,7 @@ def above_limit
     end
 
     def throttle_count
-      described_class.cache.read("#{counter_prefix}:#{throttle}:#{remote_ip}") || 0
+      described_class.cache.read("#{counter_prefix}:#{throttle}:#{discriminator}") || 0
     end
 
     def counter_prefix
@@ -64,11 +64,12 @@ def counter_prefix
     end
 
     def increment_counter
-      described_class.cache.count("#{throttle}:#{remote_ip}", period)
+      described_class.cache.count("#{throttle}:#{discriminator}", period)
     end
   end
 
   let(:remote_ip) { '1.2.3.5' }
+  let(:discriminator) { remote_ip }
 
   describe 'throttle excessive sign-up requests by IP address' do
     context 'when accessed through the website' do
@@ -149,4 +150,30 @@ def increment_counter
 
     it_behaves_like 'throttled endpoint'
   end
+
+  describe 'throttle excessive password change requests by account' do
+    let(:user) { Fabricate(:user, email: 'user@host.example') }
+    let(:throttle) { 'throttle_password_change/account' }
+    let(:limit) { 10 }
+    let(:period) { 10.minutes }
+    let(:request) { -> { put path, headers: { 'REMOTE_ADDR' => remote_ip } } }
+    let(:path) { '/auth' }
+    let(:discriminator) { user.id }
+
+    before do
+      sign_in user, scope: :user
+
+      # Unfortunately, devise's `sign_in` helper causes the `session` to be
+      # loaded in the next request regardless of whether it's actually accessed
+      # by the client code.
+      #
+      # So, we make an extra query to clear issue a session cookie instead.
+      #
+      # A less resource-intensive way to deal with that would be to generate the
+      # session cookie manually, but this seems pretty involved.
+      get '/'
+    end
+
+    it_behaves_like 'throttled endpoint'
+  end
 end
diff --git a/spec/services/notify_service_spec.rb b/spec/services/notify_service_spec.rb
index 514f634d7fde5d..6064d2b050f4a3 100644
--- a/spec/services/notify_service_spec.rb
+++ b/spec/services/notify_service_spec.rb
@@ -309,6 +309,19 @@
               expect(subject.filter?).to be false
             end
           end
+
+          context 'when the sender is mentioned in an unrelated message chain' do
+            before do
+              original_status = Fabricate(:status, visibility: :direct)
+              intermediary_status = Fabricate(:status, visibility: :direct, thread: original_status)
+              notification.target_status.update(thread: intermediary_status)
+              Fabricate(:mention, status: original_status, account: notification.from_account)
+            end
+
+            it 'returns true' do
+              expect(subject.filter?).to be true
+            end
+          end
         end
       end
     end