diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6f775fcfa8cc5e..a53790afafb8d1 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,101 @@
 
 All notable changes to this project will be documented in this file.
 
+## [4.2.7] - 2024-02-16
+
+### Fixed
+
+- Fix OmniAuth tests and edge cases in error handling ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/29201), [ClearlyClaire](https://github.com/mastodon/mastodon/pull/29207))
+- Fix new installs by upgrading to the latest release of the `nsa` gem, instead of a no longer existing commit ([mjankowski](https://github.com/mastodon/mastodon/pull/29065))
+
+### Security
+
+- Fix insufficient checking of remote posts ([GHSA-jhrq-qvrm-qr36](https://github.com/mastodon/mastodon/security/advisories/GHSA-jhrq-qvrm-qr36))
+
+## [4.2.6] - 2024-02-14
+
+### Security
+
+- Update the `sidekiq-unique-jobs` dependency (see [GHSA-cmh9-rx85-xj38](https://github.com/mhenrixon/sidekiq-unique-jobs/security/advisories/GHSA-cmh9-rx85-xj38))
+  In addition, we have disabled the web interface for `sidekiq-unique-jobs` out of caution.
+  If you need it, you can re-enable it by setting `ENABLE_SIDEKIQ_UNIQUE_JOBS_UI=true`.
+  If you only need to clear all locks, you can now use `bundle exec rake sidekiq_unique_jobs:delete_all_locks`.
+- Update the `nokogiri` dependency (see [GHSA-xc9x-jj77-9p9j](https://github.com/sparklemotion/nokogiri/security/advisories/GHSA-xc9x-jj77-9p9j))
+- Disable administrative Doorkeeper routes ([ThisIsMissEm](https://github.com/mastodon/mastodon/pull/29187))
+- Fix ongoing streaming sessions not being invalidated when applications get deleted in some cases ([GHSA-7w3c-p9j8-mq3x](https://github.com/mastodon/mastodon/security/advisories/GHSA-7w3c-p9j8-mq3x))
+  In some rare cases, the streaming server was not notified of access tokens revocation on application deletion.
+- Change external authentication behavior to never reattach a new identity to an existing user by default ([GHSA-vm39-j3vx-pch3](https://github.com/mastodon/mastodon/security/advisories/GHSA-vm39-j3vx-pch3))
+  Up until now, Mastodon has allowed new identities from external authentication providers to attach to an existing local user based on their verified e-mail address.
+  This allowed upgrading users from a database-stored password to an external authentication provider, or move from one authentication provider to another.
+  However, this behavior may be unexpected, and means that when multiple authentication providers are configured, the overall security would be that of the least secure authentication provider.
+  For these reasons, this behavior is now locked under the `ALLOW_UNSAFE_AUTH_PROVIDER_REATTACH` environment variable.
+  In addition, regardless of this environment variable, Mastodon will refuse to attach two identities from the same authentication provider to the same account.
+
+## [4.2.5] - 2024-02-01
+
+### Security
+
+- Fix insufficient origin validation (CVE-2024-23832, [GHSA-3fjr-858r-92rw](https://github.com/mastodon/mastodon/security/advisories/GHSA-3fjr-858r-92rw))
+
+## [4.2.4] - 2024-01-24
+
+### Fixed
+
+- Fix error when processing remote files with unusually long names ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/28823))
+- Fix processing of compacted single-item JSON-LD collections ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/28816))
+- Retry 401 errors on replies fetching ([ShadowJonathan](https://github.com/mastodon/mastodon/pull/28788))
+- Fix `RecordNotUnique` errors in LinkCrawlWorker ([tribela](https://github.com/mastodon/mastodon/pull/28748))
+- Fix Mastodon not correctly processing HTTP Signatures with query strings ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/28443), [ClearlyClaire](https://github.com/mastodon/mastodon/pull/28476))
+- Fix potential redirection loop of streaming endpoint ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/28665))
+- Fix streaming API redirection ignoring the port of `streaming_api_base_url` ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/28558))
+- Fix error when processing link preview with an array as `inLanguage` ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/28252))
+- Fix unsupported time zone or locale preventing sign-up ([Gargron](https://github.com/mastodon/mastodon/pull/28035))
+- Fix "Hide these posts from home" list setting not refreshing when switching lists ([brianholley](https://github.com/mastodon/mastodon/pull/27763))
+- Fix missing background behind dismissable banner in web UI ([Gargron](https://github.com/mastodon/mastodon/pull/27479))
+- Fix line wrapping of language selection button with long locale codes ([gunchleoc](https://github.com/mastodon/mastodon/pull/27100), [ClearlyClaire](https://github.com/mastodon/mastodon/pull/27127))
+- Fix `Undo Announce` activity not being sent to non-follower authors ([MitarashiDango](https://github.com/mastodon/mastodon/pull/18482))
+- Fix N+1s because of association preloaders not actually getting called ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/28339))
+- Fix empty column explainer getting cropped under certain conditions ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/28337))
+- Fix `LinkCrawlWorker` error when encountering empty OEmbed response ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/28268))
+- Fix call to inefficient `delete_matched` cache method in domain blocks ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/28367))
+
+### Security
+
+- Add rate-limit of TOTP authentication attempts at controller level ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/28801))
+
+## [4.2.3] - 2023-12-05
+
+### Fixed
+
+- Fix dependency on `json-canonicalization` version that has been made unavailable since last release
+
+## [4.2.2] - 2023-12-04
+
+### Changed
+
+- Change dismissed banners to be stored server-side ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/27055))
+- Change GIF max matrix size error to explicitly mention GIF files ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/27927))
+- Change `Follow` activities delivery to bypass availability check ([ShadowJonathan](https://github.com/mastodon/mastodon/pull/27586))
+- Change single-column navigation notice to be displayed outside of the logo container ([renchap](https://github.com/mastodon/mastodon/pull/27462), [renchap](https://github.com/mastodon/mastodon/pull/27476))
+- Change Content-Security-Policy to be tighter on media paths ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/26889))
+- Change post language code to include country code when relevant ([gunchleoc](https://github.com/mastodon/mastodon/pull/27099), [ClearlyClaire](https://github.com/mastodon/mastodon/pull/27207))
+
+### Fixed
+
+- Fix upper border radius of onboarding columns ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/27890))
+- Fix incoming status creation date not being restricted to standard ISO8601 ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/27655), [ClearlyClaire](https://github.com/mastodon/mastodon/pull/28081))
+- Fix some posts from threads received out-of-order sometimes not being inserted into timelines ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/27653))
+- Fix posts from force-sensitized accounts being able to trend ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/27620))
+- Fix error when trying to delete already-deleted file with OpenStack Swift ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/27569))
+- Fix batch attachment deletion when using OpenStack Swift ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/27554))
+- Fix processing LDSigned activities from actors with unknown public keys ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/27474))
+- Fix error and incorrect URLs in `/api/v1/accounts/:id/featured_tags` for remote accounts ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/27459))
+- Fix report processing notice not mentioning the report number when performing a custom action ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/27442))
+- Fix handling of `inLanguage` attribute in preview card processing ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/27423))
+- Fix own posts being removed from home timeline when unfollowing a used hashtag ([kmycode](https://github.com/mastodon/mastodon/pull/27391))
+- Fix some link anchors being recognized as hashtags ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/27271), [ClearlyClaire](https://github.com/mastodon/mastodon/pull/27584))
+- Fix format-dependent redirects being cached regardless of requested format ([ClearlyClaire](https://github.com/mastodon/mastodon/pull/27634))
+
 ## [4.2.1] - 2023-10-10
 
 ### Added
diff --git a/Gemfile.lock b/Gemfile.lock
index 00ca4663a848ca..0b53df82e064de 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -505,7 +505,7 @@ GEM
     parslet (2.0.0)
     pastel (0.8.0)
       tty-color (~> 0.5)
-    pg (1.5.4)
+    pg (1.5.5)
     pghero (3.4.1)
       activerecord (>= 6)
     posix-spawn (0.3.15)
diff --git a/app/controllers/auth/omniauth_callbacks_controller.rb b/app/controllers/auth/omniauth_callbacks_controller.rb
index 9b83de945bee2a..9d496220a3d277 100644
--- a/app/controllers/auth/omniauth_callbacks_controller.rb
+++ b/app/controllers/auth/omniauth_callbacks_controller.rb
@@ -17,6 +17,9 @@ def self.provides_callback_for(provider)
         session["devise.#{provider}_data"] = request.env['omniauth.auth']
         redirect_to new_user_registration_url
       end
+    rescue ActiveRecord::RecordInvalid
+      flash[:alert] = I18n.t('devise.failure.omniauth_user_creation_failure') if is_navigational_format?
+      redirect_to new_user_session_url
     end
   end
 
diff --git a/app/helpers/jsonld_helper.rb b/app/helpers/jsonld_helper.rb
index cc05b7a403483e..b0f2077db0e501 100644
--- a/app/helpers/jsonld_helper.rb
+++ b/app/helpers/jsonld_helper.rb
@@ -174,7 +174,19 @@ def fetch_resource_without_id_validation(uri, on_behalf_of = nil, raise_on_tempo
     build_request(uri, on_behalf_of, options: request_options).perform do |response|
       raise Mastodon::UnexpectedResponseError, response unless response_successful?(response) || response_error_unsalvageable?(response) || !raise_on_temporary_error
 
-      body_to_json(response.body_with_limit) if response.code == 200
+      body_to_json(response.body_with_limit) if response.code == 200 && valid_activitypub_content_type?(response)
+    end
+  end
+
+  def valid_activitypub_content_type?(response)
+    return true if response.mime_type == 'application/activity+json'
+
+    # When the mime type is `application/ld+json`, we need to check the profile,
+    # but `http.rb` does not parse it for us.
+    return false unless response.mime_type == 'application/ld+json'
+
+    response.headers[HTTP::Headers::CONTENT_TYPE]&.split(';')&.map(&:strip)&.any? do |str|
+      str.start_with?('profile="') && str[9...-1].split.include?('https://www.w3.org/ns/activitystreams')
     end
   end
 
diff --git a/app/services/fetch_resource_service.rb b/app/services/fetch_resource_service.rb
index 71c6cca790c6ee..84c36f6a1014b8 100644
--- a/app/services/fetch_resource_service.rb
+++ b/app/services/fetch_resource_service.rb
@@ -44,7 +44,7 @@ def process_response(response, terminal = false)
     @response_code = response.code
     return nil if response.code != 200
 
-    if ['application/activity+json', 'application/ld+json'].include?(response.mime_type)
+    if valid_activitypub_content_type?(response)
       body = response.body_with_limit
       json = body_to_json(body)
 
diff --git a/config/locales/devise.en.yml b/config/locales/devise.en.yml
index 4439397c8eead1..61bd33851b6fca 100644
--- a/config/locales/devise.en.yml
+++ b/config/locales/devise.en.yml
@@ -12,6 +12,7 @@ en:
       last_attempt: You have one more attempt before your account is locked.
       locked: Your account is locked.
       not_found_in_database: Invalid %{authentication_keys} or password.
+      omniauth_user_creation_failure: Error creating an account for this identity.
       pending: Your account is still under review.
       timeout: Your session expired. Please login again to continue.
       unauthenticated: You need to login or sign up before continuing.
diff --git a/docker-compose.yml b/docker-compose.yml
index 93451d9611036a..154754d45f61bd 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -56,7 +56,7 @@ services:
 
   web:
     build: .
-    image: ghcr.io/mastodon/mastodon:v4.2.0
+    image: ghcr.io/mastodon/mastodon:v4.2.7
     restart: always
     env_file: .env.production
     command: bundle exec puma -C config/puma.rb
@@ -77,7 +77,7 @@ services:
 
   streaming:
     build: .
-    image: ghcr.io/mastodon/mastodon:v4.2.0
+    image: ghcr.io/mastodon/mastodon:v4.2.7
     restart: always
     env_file: .env.production
     command: node ./streaming
@@ -95,7 +95,7 @@ services:
 
   sidekiq:
     build: .
-    image: ghcr.io/mastodon/mastodon:v4.2.0
+    image: ghcr.io/mastodon/mastodon:v4.2.7
     restart: always
     env_file: .env.production
     command: bundle exec sidekiq
diff --git a/lib/mastodon/version.rb b/lib/mastodon/version.rb
index 57c578ec44f7de..dcb24b6b20a40f 100644
--- a/lib/mastodon/version.rb
+++ b/lib/mastodon/version.rb
@@ -17,7 +17,7 @@ def patch
     end
 
     def default_prerelease
-      'alpha.2'
+      'alpha.3'
     end
 
     def prerelease
diff --git a/spec/helpers/json_ld_helper_spec.rb b/spec/helpers/json_ld_helper_spec.rb
index 99857278a14c66..48550850274e01 100644
--- a/spec/helpers/json_ld_helper_spec.rb
+++ b/spec/helpers/json_ld_helper_spec.rb
@@ -56,15 +56,15 @@
   describe '#fetch_resource' do
     context 'when the second argument is false' do
       it 'returns resource even if the retrieved ID and the given URI does not match' do
-        stub_request(:get, 'https://bob.test/').to_return body: '{"id": "https://alice.test/"}'
-        stub_request(:get, 'https://alice.test/').to_return body: '{"id": "https://alice.test/"}'
+        stub_request(:get, 'https://bob.test/').to_return(body: '{"id": "https://alice.test/"}', headers: { 'Content-Type': 'application/activity+json' })
+        stub_request(:get, 'https://alice.test/').to_return(body: '{"id": "https://alice.test/"}', headers: { 'Content-Type': 'application/activity+json' })
 
         expect(fetch_resource('https://bob.test/', false)).to eq({ 'id' => 'https://alice.test/' })
       end
 
       it 'returns nil if the object identified by the given URI and the object identified by the retrieved ID does not match' do
-        stub_request(:get, 'https://mallory.test/').to_return body: '{"id": "https://marvin.test/"}'
-        stub_request(:get, 'https://marvin.test/').to_return body: '{"id": "https://alice.test/"}'
+        stub_request(:get, 'https://mallory.test/').to_return(body: '{"id": "https://marvin.test/"}', headers: { 'Content-Type': 'application/activity+json' })
+        stub_request(:get, 'https://marvin.test/').to_return(body: '{"id": "https://alice.test/"}', headers: { 'Content-Type': 'application/activity+json' })
 
         expect(fetch_resource('https://mallory.test/', false)).to be_nil
       end
@@ -72,7 +72,7 @@
 
     context 'when the second argument is true' do
       it 'returns nil if the retrieved ID and the given URI does not match' do
-        stub_request(:get, 'https://mallory.test/').to_return body: '{"id": "https://alice.test/"}'
+        stub_request(:get, 'https://mallory.test/').to_return(body: '{"id": "https://alice.test/"}', headers: { 'Content-Type': 'application/activity+json' })
         expect(fetch_resource('https://mallory.test/', true)).to be_nil
       end
     end
@@ -80,12 +80,12 @@
 
   describe '#fetch_resource_without_id_validation' do
     it 'returns nil if the status code is not 200' do
-      stub_request(:get, 'https://host.test/').to_return status: 400, body: '{}'
+      stub_request(:get, 'https://host.test/').to_return(status: 400, body: '{}', headers: { 'Content-Type': 'application/activity+json' })
       expect(fetch_resource_without_id_validation('https://host.test/')).to be_nil
     end
 
     it 'returns hash' do
-      stub_request(:get, 'https://host.test/').to_return status: 200, body: '{}'
+      stub_request(:get, 'https://host.test/').to_return(status: 200, body: '{}', headers: { 'Content-Type': 'application/activity+json' })
       expect(fetch_resource_without_id_validation('https://host.test/')).to eq({})
     end
   end
diff --git a/spec/lib/activitypub/activity/announce_spec.rb b/spec/lib/activitypub/activity/announce_spec.rb
index 8ad892975d13c5..b556bfd6c2ece3 100644
--- a/spec/lib/activitypub/activity/announce_spec.rb
+++ b/spec/lib/activitypub/activity/announce_spec.rb
@@ -35,7 +35,7 @@
     context 'when sender is followed by a local account' do
       before do
         Fabricate(:account).follow!(sender)
-        stub_request(:get, 'https://example.com/actor/hello-world').to_return(body: Oj.dump(unknown_object_json))
+        stub_request(:get, 'https://example.com/actor/hello-world').to_return(body: Oj.dump(unknown_object_json), headers: { 'Content-Type': 'application/activity+json' })
         subject.perform
       end
 
@@ -120,7 +120,7 @@
       let(:object_json) { 'https://example.com/actor/hello-world' }
 
       before do
-        stub_request(:get, 'https://example.com/actor/hello-world').to_return(body: Oj.dump(unknown_object_json))
+        stub_request(:get, 'https://example.com/actor/hello-world').to_return(body: Oj.dump(unknown_object_json), headers: { 'Content-Type': 'application/activity+json' })
       end
 
       context 'when the relay is enabled' do
diff --git a/spec/requests/omniauth_callbacks_spec.rb b/spec/requests/omniauth_callbacks_spec.rb
index 1e488b3f43fc3a..095535e48598e0 100644
--- a/spec/requests/omniauth_callbacks_spec.rb
+++ b/spec/requests/omniauth_callbacks_spec.rb
@@ -60,11 +60,13 @@
         end
 
         context 'when ALLOW_UNSAFE_AUTH_PROVIDER_REATTACH is not set to true' do
-          it 'does not match the existing user or create an identity' do
+          it 'does not match the existing user or create an identity, and redirects to login page' do
             expect { subject }
               .to not_change(User, :count)
               .and not_change(Identity, :count)
               .and not_change(LoginActivity, :count)
+
+            expect(response).to redirect_to(new_user_session_url)
           end
         end
       end
diff --git a/spec/services/activitypub/fetch_featured_collection_service_spec.rb b/spec/services/activitypub/fetch_featured_collection_service_spec.rb
index b9e95b825f553c..dab204406bbb23 100644
--- a/spec/services/activitypub/fetch_featured_collection_service_spec.rb
+++ b/spec/services/activitypub/fetch_featured_collection_service_spec.rb
@@ -72,11 +72,11 @@
 
   shared_examples 'sets pinned posts' do
     before do
-      stub_request(:get, 'https://example.com/account/pinned/known').to_return(status: 200, body: Oj.dump(status_json_pinned_known))
-      stub_request(:get, 'https://example.com/account/pinned/unknown-inlined').to_return(status: 200, body: Oj.dump(status_json_pinned_unknown_inlined))
+      stub_request(:get, 'https://example.com/account/pinned/known').to_return(status: 200, body: Oj.dump(status_json_pinned_known), headers: { 'Content-Type': 'application/activity+json' })
+      stub_request(:get, 'https://example.com/account/pinned/unknown-inlined').to_return(status: 200, body: Oj.dump(status_json_pinned_unknown_inlined), headers: { 'Content-Type': 'application/activity+json' })
       stub_request(:get, 'https://example.com/account/pinned/unknown-unreachable').to_return(status: 404)
-      stub_request(:get, 'https://example.com/account/pinned/unknown-reachable').to_return(status: 200, body: Oj.dump(status_json_pinned_unknown_reachable))
-      stub_request(:get, 'https://example.com/account/collections/featured').to_return(status: 200, body: Oj.dump(featured_with_null))
+      stub_request(:get, 'https://example.com/account/pinned/unknown-reachable').to_return(status: 200, body: Oj.dump(status_json_pinned_unknown_reachable), headers: { 'Content-Type': 'application/activity+json' })
+      stub_request(:get, 'https://example.com/account/collections/featured').to_return(status: 200, body: Oj.dump(featured_with_null), headers: { 'Content-Type': 'application/activity+json' })
 
       subject.call(actor, note: true, hashtag: false)
     end
@@ -94,7 +94,7 @@
   describe '#call' do
     context 'when the endpoint is a Collection' do
       before do
-        stub_request(:get, actor.featured_collection_url).to_return(status: 200, body: Oj.dump(payload))
+        stub_request(:get, actor.featured_collection_url).to_return(status: 200, body: Oj.dump(payload), headers: { 'Content-Type': 'application/activity+json' })
       end
 
       it_behaves_like 'sets pinned posts'
@@ -111,7 +111,7 @@
       end
 
       before do
-        stub_request(:get, actor.featured_collection_url).to_return(status: 200, body: Oj.dump(payload))
+        stub_request(:get, actor.featured_collection_url).to_return(status: 200, body: Oj.dump(payload), headers: { 'Content-Type': 'application/activity+json' })
       end
 
       it_behaves_like 'sets pinned posts'
@@ -120,7 +120,7 @@
         let(:items) { 'https://example.com/account/pinned/unknown-reachable' }
 
         before do
-          stub_request(:get, 'https://example.com/account/pinned/unknown-reachable').to_return(status: 200, body: Oj.dump(status_json_pinned_unknown_reachable))
+          stub_request(:get, 'https://example.com/account/pinned/unknown-reachable').to_return(status: 200, body: Oj.dump(status_json_pinned_unknown_reachable), headers: { 'Content-Type': 'application/activity+json' })
           subject.call(actor, note: true, hashtag: false)
         end
 
@@ -147,7 +147,7 @@
       end
 
       before do
-        stub_request(:get, actor.featured_collection_url).to_return(status: 200, body: Oj.dump(payload))
+        stub_request(:get, actor.featured_collection_url).to_return(status: 200, body: Oj.dump(payload), headers: { 'Content-Type': 'application/activity+json' })
       end
 
       it_behaves_like 'sets pinned posts'
@@ -156,7 +156,7 @@
         let(:items) { 'https://example.com/account/pinned/unknown-reachable' }
 
         before do
-          stub_request(:get, 'https://example.com/account/pinned/unknown-reachable').to_return(status: 200, body: Oj.dump(status_json_pinned_unknown_reachable))
+          stub_request(:get, 'https://example.com/account/pinned/unknown-reachable').to_return(status: 200, body: Oj.dump(status_json_pinned_unknown_reachable), headers: { 'Content-Type': 'application/activity+json' })
           subject.call(actor, note: true, hashtag: false)
         end
 
diff --git a/spec/services/activitypub/fetch_featured_tags_collection_service_spec.rb b/spec/services/activitypub/fetch_featured_tags_collection_service_spec.rb
index 071e4d92d59865..638278a10e5375 100644
--- a/spec/services/activitypub/fetch_featured_tags_collection_service_spec.rb
+++ b/spec/services/activitypub/fetch_featured_tags_collection_service_spec.rb
@@ -38,7 +38,7 @@
   describe '#call' do
     context 'when the endpoint is a Collection' do
       before do
-        stub_request(:get, collection_url).to_return(status: 200, body: Oj.dump(payload))
+        stub_request(:get, collection_url).to_return(status: 200, body: Oj.dump(payload), headers: { 'Content-Type': 'application/activity+json' })
       end
 
       it_behaves_like 'sets featured tags'
@@ -46,7 +46,7 @@
 
     context 'when the account already has featured tags' do
       before do
-        stub_request(:get, collection_url).to_return(status: 200, body: Oj.dump(payload))
+        stub_request(:get, collection_url).to_return(status: 200, body: Oj.dump(payload), headers: { 'Content-Type': 'application/activity+json' })
 
         actor.featured_tags.create!(name: 'FoO')
         actor.featured_tags.create!(name: 'baz')
@@ -67,7 +67,7 @@
       end
 
       before do
-        stub_request(:get, collection_url).to_return(status: 200, body: Oj.dump(payload))
+        stub_request(:get, collection_url).to_return(status: 200, body: Oj.dump(payload), headers: { 'Content-Type': 'application/activity+json' })
       end
 
       it_behaves_like 'sets featured tags'
@@ -88,7 +88,7 @@
       end
 
       before do
-        stub_request(:get, collection_url).to_return(status: 200, body: Oj.dump(payload))
+        stub_request(:get, collection_url).to_return(status: 200, body: Oj.dump(payload), headers: { 'Content-Type': 'application/activity+json' })
       end
 
       it_behaves_like 'sets featured tags'
diff --git a/spec/services/activitypub/fetch_remote_account_service_spec.rb b/spec/services/activitypub/fetch_remote_account_service_spec.rb
index f33a928da6dd2c..42badde0517980 100644
--- a/spec/services/activitypub/fetch_remote_account_service_spec.rb
+++ b/spec/services/activitypub/fetch_remote_account_service_spec.rb
@@ -44,7 +44,7 @@
       before do
         actor[:inbox] = nil
 
-        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor))
+        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor), headers: { 'Content-Type': 'application/activity+json' })
         stub_request(:get, 'https://example.com/.well-known/webfinger?resource=acct:alice@example.com').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
       end
 
@@ -67,7 +67,7 @@
       let!(:webfinger) { { subject: 'acct:alice@example.com', links: [{ rel: 'self', href: 'https://example.com/alice' }] } }
 
       before do
-        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor))
+        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor), headers: { 'Content-Type': 'application/activity+json' })
         stub_request(:get, 'https://example.com/.well-known/webfinger?resource=acct:alice@example.com').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
       end
 
@@ -93,7 +93,7 @@
       let!(:webfinger) { { subject: 'acct:alice@iscool.af', links: [{ rel: 'self', href: 'https://example.com/alice' }] } }
 
       before do
-        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor))
+        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor), headers: { 'Content-Type': 'application/activity+json' })
         stub_request(:get, 'https://example.com/.well-known/webfinger?resource=acct:alice@example.com').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
         stub_request(:get, 'https://iscool.af/.well-known/webfinger?resource=acct:alice@iscool.af').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
       end
@@ -125,7 +125,7 @@
       let!(:webfinger) { { subject: 'acct:alice@example.com', links: [{ rel: 'self', href: 'https://example.com/bob' }] } }
 
       before do
-        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor))
+        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor), headers: { 'Content-Type': 'application/activity+json' })
         stub_request(:get, 'https://example.com/.well-known/webfinger?resource=acct:alice@example.com').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
       end
 
@@ -148,7 +148,7 @@
       let!(:webfinger) { { subject: 'acct:alice@iscool.af', links: [{ rel: 'self', href: 'https://example.com/bob' }] } }
 
       before do
-        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor))
+        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor), headers: { 'Content-Type': 'application/activity+json' })
         stub_request(:get, 'https://example.com/.well-known/webfinger?resource=acct:alice@example.com').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
         stub_request(:get, 'https://iscool.af/.well-known/webfinger?resource=acct:alice@iscool.af').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
       end
diff --git a/spec/services/activitypub/fetch_remote_actor_service_spec.rb b/spec/services/activitypub/fetch_remote_actor_service_spec.rb
index 944a2f8b1c63eb..6d264b7b825276 100644
--- a/spec/services/activitypub/fetch_remote_actor_service_spec.rb
+++ b/spec/services/activitypub/fetch_remote_actor_service_spec.rb
@@ -44,7 +44,7 @@
       before do
         actor[:inbox] = nil
 
-        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor))
+        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor), headers: { 'Content-Type': 'application/activity+json' })
         stub_request(:get, 'https://example.com/.well-known/webfinger?resource=acct:alice@example.com').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
       end
 
@@ -67,7 +67,7 @@
       let!(:webfinger) { { subject: 'acct:alice@example.com', links: [{ rel: 'self', href: 'https://example.com/alice' }] } }
 
       before do
-        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor))
+        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor), headers: { 'Content-Type': 'application/activity+json' })
         stub_request(:get, 'https://example.com/.well-known/webfinger?resource=acct:alice@example.com').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
       end
 
@@ -93,7 +93,7 @@
       let!(:webfinger) { { subject: 'acct:alice@iscool.af', links: [{ rel: 'self', href: 'https://example.com/alice' }] } }
 
       before do
-        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor))
+        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor), headers: { 'Content-Type': 'application/activity+json' })
         stub_request(:get, 'https://example.com/.well-known/webfinger?resource=acct:alice@example.com').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
         stub_request(:get, 'https://iscool.af/.well-known/webfinger?resource=acct:alice@iscool.af').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
       end
@@ -125,7 +125,7 @@
       let!(:webfinger) { { subject: 'acct:alice@example.com', links: [{ rel: 'self', href: 'https://example.com/bob' }] } }
 
       before do
-        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor))
+        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor), headers: { 'Content-Type': 'application/activity+json' })
         stub_request(:get, 'https://example.com/.well-known/webfinger?resource=acct:alice@example.com').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
       end
 
@@ -148,7 +148,7 @@
       let!(:webfinger) { { subject: 'acct:alice@iscool.af', links: [{ rel: 'self', href: 'https://example.com/bob' }] } }
 
       before do
-        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor))
+        stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor), headers: { 'Content-Type': 'application/activity+json' })
         stub_request(:get, 'https://example.com/.well-known/webfinger?resource=acct:alice@example.com').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
         stub_request(:get, 'https://iscool.af/.well-known/webfinger?resource=acct:alice@iscool.af').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
       end
diff --git a/spec/services/activitypub/fetch_remote_key_service_spec.rb b/spec/services/activitypub/fetch_remote_key_service_spec.rb
index 0b14da4f446e5f..478778cc9f5762 100644
--- a/spec/services/activitypub/fetch_remote_key_service_spec.rb
+++ b/spec/services/activitypub/fetch_remote_key_service_spec.rb
@@ -50,7 +50,7 @@
   end
 
   before do
-    stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor))
+    stub_request(:get, 'https://example.com/alice').to_return(body: Oj.dump(actor), headers: { 'Content-Type': 'application/activity+json' })
     stub_request(:get, 'https://example.com/.well-known/webfinger?resource=acct:alice@example.com').to_return(body: Oj.dump(webfinger), headers: { 'Content-Type': 'application/jrd+json' })
   end
 
@@ -59,7 +59,7 @@
 
     context 'when the key is a sub-object from the actor' do
       before do
-        stub_request(:get, public_key_id).to_return(body: Oj.dump(actor))
+        stub_request(:get, public_key_id).to_return(body: Oj.dump(actor), headers: { 'Content-Type': 'application/activity+json' })
       end
 
       it 'returns the expected account' do
@@ -71,7 +71,7 @@
       let(:public_key_id) { 'https://example.com/alice-public-key.json' }
 
       before do
-        stub_request(:get, public_key_id).to_return(body: Oj.dump(key_json.merge({ '@context': ['https://www.w3.org/ns/activitystreams', 'https://w3id.org/security/v1'] })))
+        stub_request(:get, public_key_id).to_return(body: Oj.dump(key_json.merge({ '@context': ['https://www.w3.org/ns/activitystreams', 'https://w3id.org/security/v1'] })), headers: { 'Content-Type': 'application/activity+json' })
       end
 
       it 'returns the expected account' do
@@ -84,7 +84,7 @@
       let(:actor_public_key) { 'https://example.com/alice-public-key.json' }
 
       before do
-        stub_request(:get, public_key_id).to_return(body: Oj.dump(key_json.merge({ '@context': ['https://www.w3.org/ns/activitystreams', 'https://w3id.org/security/v1'] })))
+        stub_request(:get, public_key_id).to_return(body: Oj.dump(key_json.merge({ '@context': ['https://www.w3.org/ns/activitystreams', 'https://w3id.org/security/v1'] })), headers: { 'Content-Type': 'application/activity+json' })
       end
 
       it 'returns the nil' do
diff --git a/spec/services/activitypub/fetch_replies_service_spec.rb b/spec/services/activitypub/fetch_replies_service_spec.rb
index a76b996c20fcd6..8e1f606e26e794 100644
--- a/spec/services/activitypub/fetch_replies_service_spec.rb
+++ b/spec/services/activitypub/fetch_replies_service_spec.rb
@@ -58,7 +58,7 @@
 
       context 'when passing the URL to the collection' do
         before do
-          stub_request(:get, collection_uri).to_return(status: 200, body: Oj.dump(payload))
+          stub_request(:get, collection_uri).to_return(status: 200, body: Oj.dump(payload), headers: { 'Content-Type': 'application/activity+json' })
         end
 
         it 'spawns workers for up to 5 replies on the same server' do
@@ -93,7 +93,7 @@
 
       context 'when passing the URL to the collection' do
         before do
-          stub_request(:get, collection_uri).to_return(status: 200, body: Oj.dump(payload))
+          stub_request(:get, collection_uri).to_return(status: 200, body: Oj.dump(payload), headers: { 'Content-Type': 'application/activity+json' })
         end
 
         it 'spawns workers for up to 5 replies on the same server' do
@@ -132,7 +132,7 @@
 
       context 'when passing the URL to the collection' do
         before do
-          stub_request(:get, collection_uri).to_return(status: 200, body: Oj.dump(payload))
+          stub_request(:get, collection_uri).to_return(status: 200, body: Oj.dump(payload), headers: { 'Content-Type': 'application/activity+json' })
         end
 
         it 'spawns workers for up to 5 replies on the same server' do
diff --git a/spec/services/activitypub/synchronize_followers_service_spec.rb b/spec/services/activitypub/synchronize_followers_service_spec.rb
index c9a513e24b7c3b..f62376ab95b24e 100644
--- a/spec/services/activitypub/synchronize_followers_service_spec.rb
+++ b/spec/services/activitypub/synchronize_followers_service_spec.rb
@@ -60,7 +60,7 @@
   describe '#call' do
     context 'when the endpoint is a Collection of actor URIs' do
       before do
-        stub_request(:get, collection_uri).to_return(status: 200, body: Oj.dump(payload))
+        stub_request(:get, collection_uri).to_return(status: 200, body: Oj.dump(payload), headers: { 'Content-Type': 'application/activity+json' })
       end
 
       it_behaves_like 'synchronizes followers'
@@ -77,7 +77,7 @@
       end
 
       before do
-        stub_request(:get, collection_uri).to_return(status: 200, body: Oj.dump(payload))
+        stub_request(:get, collection_uri).to_return(status: 200, body: Oj.dump(payload), headers: { 'Content-Type': 'application/activity+json' })
       end
 
       it_behaves_like 'synchronizes followers'
@@ -98,7 +98,7 @@
       end
 
       before do
-        stub_request(:get, collection_uri).to_return(status: 200, body: Oj.dump(payload))
+        stub_request(:get, collection_uri).to_return(status: 200, body: Oj.dump(payload), headers: { 'Content-Type': 'application/activity+json' })
       end
 
       it_behaves_like 'synchronizes followers'
diff --git a/spec/workers/activitypub/fetch_replies_worker_spec.rb b/spec/workers/activitypub/fetch_replies_worker_spec.rb
index ff4d049a269ed9..2d080e286ecc98 100644
--- a/spec/workers/activitypub/fetch_replies_worker_spec.rb
+++ b/spec/workers/activitypub/fetch_replies_worker_spec.rb
@@ -21,7 +21,7 @@
 
   describe 'perform' do
     it 'performs a request if the collection URI is from the same host' do
-      stub_request(:get, 'https://example.com/statuses_replies/1').to_return(status: 200, body: json)
+      stub_request(:get, 'https://example.com/statuses_replies/1').to_return(status: 200, body: json, headers: { 'Content-Type': 'application/activity+json' })
       subject.perform(status.id, 'https://example.com/statuses_replies/1')
       expect(a_request(:get, 'https://example.com/statuses_replies/1')).to have_been_made.once
     end