diff --git a/Gemfile b/Gemfile
index f7aef2fe02bd7..e9a36324d6e83 100644
--- a/Gemfile
+++ b/Gemfile
@@ -73,7 +73,7 @@ gem "omniauth-apple", "~> 1.0" # OmniAuth strategy for Sign In with Apple
 gem "omniauth-facebook", "~> 9.0" # OmniAuth strategy for Facebook
 gem "omniauth-github", "~> 2.0" # OmniAuth strategy for GitHub
 gem "omniauth-google-oauth2", "~> 1.0" # OmniAuth strategy for Google OAuth2
-gem "omniauth-mlh", "~> 4.1"
+gem "omniauth-mlh", "~> 4.2"
 gem "omniauth-rails_csrf_protection", "~> 2.0" # Provides CSRF protection on OmniAuth request endpoint on Rails application.
 gem "omniauth-twitter", "~> 1.4" # OmniAuth strategy for Twitter
 gem "parallel", "~> 1.22" # Run any kind of code in parallel processes
diff --git a/Gemfile.lock b/Gemfile.lock
index f542d0235f4a3..38c9333d65c39 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -675,7 +675,7 @@ GEM
       oauth2 (~> 2.0)
       omniauth (~> 2.0)
       omniauth-oauth2 (~> 1.8)
-    omniauth-mlh (4.1.0)
+    omniauth-mlh (4.2.0)
       oauth2 (~> 2.0.9)
       omniauth (~> 2.1.1)
       omniauth-oauth2 (~> 1.8.0)
@@ -1207,7 +1207,7 @@ DEPENDENCIES
   omniauth-facebook (~> 9.0)
   omniauth-github (~> 2.0)
   omniauth-google-oauth2 (~> 1.0)
-  omniauth-mlh (~> 4.1)
+  omniauth-mlh (~> 4.2)
   omniauth-rails_csrf_protection (~> 2.0)
   omniauth-twitter (~> 1.4)
   parallel (~> 1.22)
diff --git a/app/errors/authentication/errors.rb b/app/errors/authentication/errors.rb
index c1860e6897669..a65deb6ae4cf7 100644
--- a/app/errors/authentication/errors.rb
+++ b/app/errors/authentication/errors.rb
@@ -20,5 +20,20 @@ def message
     # Raised when we find an email that's from a spammy domain.
     class SpammyEmailDomain < Error
     end
+
+    class Ineligible < Error
+      def message
+        I18n.t("services.authentication.authenticator.account_not_eligible")
+      end
+    end
+
+    class AccountSwitchConfirmation < Error
+      attr_reader :target_user
+
+      def initialize(target_user)
+        @target_user = target_user
+        super("account_switch_confirmation")
+      end
+    end
   end
 end
diff --git a/app/services/authentication/authenticator.rb b/app/services/authentication/authenticator.rb
index a45e7c7e405a2..364abaca43597 100644
--- a/app/services/authentication/authenticator.rb
+++ b/app/services/authentication/authenticator.rb
@@ -41,6 +41,7 @@ def call
         refresh_identity(identity, linked_identity)
         return current_user
       end
+      guard_account_switch!(identity) if current_user
 
       # These variables need to be set outside of the scope of the
       # transaction in order to be used after the transaction is completed.
@@ -169,6 +170,23 @@ def repoint_identity(incoming_identity, linked_identity)
       nil
     end
 
+    def guard_account_switch!(identity)
+      candidate = identity.user || verified_email_user
+      return if candidate.nil? || candidate == current_user
+
+      raise ::Authentication::Errors::Ineligible if candidate.spam_or_suspended?
+
+      raise ::Authentication::Errors::AccountSwitchConfirmation.new(candidate)
+    end
+
+    def verified_email_user
+      email = provider.user_email
+      return nil if email.blank?
+
+      user = User.find_by(email: email)
+      user&.confirmed? ? user : nil
+    end
+
     def proper_user(identity)
       if current_user
         Rails.logger.debug { "Current user exists: #{current_user.id}" }
diff --git a/app/views/liquids/_youtube.html.erb b/app/views/liquids/_youtube.html.erb
index d1a37c670e5c0..4fff4f5ff396c 100644
--- a/app/views/liquids/_youtube.html.erb
+++ b/app/views/liquids/_youtube.html.erb
@@ -4,7 +4,7 @@
       src="https://www.youtube.com/embed/<%= id %>"
       width="<%= local_assigns[:width] || 315 %>"
       height="<%= local_assigns[:height] || 560 %>"
-      style="width: 100%; aspect-ratio: 9 / 16;"
+      style="width: 100%; height: auto; aspect-ratio: 9 / 16;"
       allowfullscreen
       loading="lazy">
     </iframe>
@@ -14,7 +14,7 @@
     src="https://www.youtube.com/embed/<%= id %>"
     width="<%= local_assigns[:width] || 710 %>"
     height="<%= local_assigns[:height] || 399 %>"
-    style="width: 100%; aspect-ratio: 16 / 9;"
+    style="width: 100%; height: auto; aspect-ratio: 16 / 9;"
     allowfullscreen
     loading="lazy">
   </iframe>
diff --git a/config/locales/services/en.yml b/config/locales/services/en.yml
index f22f89fc8a2f6..2a69d5b90f8da 100644
--- a/config/locales/services/en.yml
+++ b/config/locales/services/en.yml
@@ -8,6 +8,7 @@ en:
     authentication:
       authenticator:
         not_allowed: Sorry, but the domain for your email address is not allowed. This Forem may have limited signup to only specified email domains or blocked this specific domain from joining.
+        account_not_eligible: Sorry, this account is not eligible to sign in. Please contact the community staff if you believe this is a mistake.
       providers:
         apple:
           name: "%{first} %{last}"
diff --git a/config/locales/services/fr.yml b/config/locales/services/fr.yml
index 7c90d12cec841..657f984a60733 100644
--- a/config/locales/services/fr.yml
+++ b/config/locales/services/fr.yml
@@ -7,6 +7,7 @@ fr:
       unpublished_video: Vidéo non publiée ~ %{rand}
     authentication:
       authenticator:
+        account_not_eligible: "Désolé, ce compte ne peut pas se connecter. Veuillez contacter l’équipe de la communauté si vous pensez qu’il s’agit d’une erreur."
         not_allowed: Désolé, mais le domaine de votre adresse e-mail n'est pas autorisé. Ce Forem a peut-être limité l'inscription à certains domaines de messagerie ou bloqué l'accès à ce domaine spécifique.
       providers:
         apple:
diff --git a/config/locales/services/pt.yml b/config/locales/services/pt.yml
index 583cd77fc9076..da62b3c49219f 100644
--- a/config/locales/services/pt.yml
+++ b/config/locales/services/pt.yml
@@ -7,6 +7,7 @@ pt:
       unpublished_video: Vídeo Não Publicado ~ %{rand}
     authentication:
       authenticator:
+        account_not_eligible: "Desculpe, esta conta não está autorizada a entrar. Entre em contato com a equipe da comunidade se você acredita que isso é um engano."
         not_allowed: Desculpe, mas o domínio do seu endereço de e-mail não é permitido. Este Forem pode ter limitado o cadastro apenas a domínios de e-mail específicos ou bloqueado este domínio específico de participar.
       providers:
         apple:
diff --git a/spec/liquid_tags/descript_tag_spec.rb b/spec/liquid_tags/descript_tag_spec.rb
index a2cdccb553e23..435b872c70266 100644
--- a/spec/liquid_tags/descript_tag_spec.rb
+++ b/spec/liquid_tags/descript_tag_spec.rb
@@ -26,6 +26,14 @@ def generate_embed(url)
   end
 
   describe "rendering" do
+    before do
+      allow(Addrinfo).to receive(:getaddrinfo).and_call_original
+      %w[www.share.descript.com share.descript.com descript.com].each do |host|
+        allow(Addrinfo).to receive(:getaddrinfo).with(host, nil, nil, :STREAM)
+          .and_return([instance_double(Addrinfo, ip_address: "34.95.113.47")])
+      end
+    end
+
     it "returns StandardError for invalid Descript URL", :aggregate_failures do
       invalid_descript_urls.each do |invalid_url|
         stub_network_request(url: invalid_url, status_code: 404)
diff --git a/spec/liquid_tags/youtube_tag_spec.rb b/spec/liquid_tags/youtube_tag_spec.rb
index 9dca95c43596c..6279a005f96c1 100644
--- a/spec/liquid_tags/youtube_tag_spec.rb
+++ b/spec/liquid_tags/youtube_tag_spec.rb
@@ -50,14 +50,14 @@ def generate_tag(input)
 
     it "uses a vertical aspect ratio for YouTube Shorts" do
       result = generate_tag("https://www.youtube.com/shorts/#{valid_id}")
-      expect(result).to include("aspect-ratio: 9 / 16")
+      expect(result).to include("width: 100%; height: auto; aspect-ratio: 9 / 16")
       expect(result).to include('width="315"')
       expect(result).to include('height="560"')
     end
 
     it "uses a horizontal aspect ratio for regular videos" do
       result = generate_tag("https://www.youtube.com/watch?v=#{valid_id}")
-      expect(result).to include("aspect-ratio: 16 / 9")
+      expect(result).to include("width: 100%; height: auto; aspect-ratio: 16 / 9")
       expect(result).to include('width="710"')
       expect(result).to include('height="399"')
     end
diff --git a/spec/services/authentication/authenticator_account_switch_spec.rb b/spec/services/authentication/authenticator_account_switch_spec.rb
new file mode 100644
index 0000000000000..d41ca8dabd2db
--- /dev/null
+++ b/spec/services/authentication/authenticator_account_switch_spec.rb
@@ -0,0 +1,79 @@
+require "rails_helper"
+
+RSpec.describe Authentication::Authenticator, type: :service do
+  let(:current_user) { create(:user) }
+
+  def mlh_payload(uid:, email:)
+    OmniAuth::AuthHash.new(
+      provider: "mlh",
+      uid: uid,
+      info: OmniAuth::AuthHash::InfoHash.new(email: email, name: "MLH User"),
+      credentials: OmniAuth::AuthHash.new(token: "tok_#{uid}", secret: "sec"),
+      extra: { raw_info: { created_at: 2.years.ago.iso8601 } },
+    )
+  end
+
+  before do
+    omniauth_mock_mlh_payload
+    allow(ForemStatsClient).to receive(:increment)
+    allow(Settings::Authentication).to receive(:providers).and_return(Authentication::Providers.available)
+  end
+
+  context "when a different user is signed in and the incoming identity resolves elsewhere" do
+    it "raises AccountSwitchConfirmation carrying the resolved target (exact verified email)" do
+      target = create(:user)
+      payload = mlh_payload(uid: "core-switch-1", email: target.email)
+
+      expect do
+        expect do
+          described_class.call(payload, current_user: current_user)
+        end.to raise_error(
+          Authentication::Errors::AccountSwitchConfirmation,
+        ) { |error| expect(error.target_user).to eq(target) }
+      end.not_to change(Identity, :count)
+    end
+
+    it "raises AccountSwitchConfirmation carrying the resolved target (uid ownership)" do
+      target = create(:user)
+      create(:identity, user: target, provider: "mlh", uid: "core-switch-2")
+      payload = mlh_payload(uid: "core-switch-2", email: "nobody-else@example.com")
+
+      expect do
+        described_class.call(payload, current_user: current_user)
+      end.to raise_error(
+        Authentication::Errors::AccountSwitchConfirmation,
+      ) { |error| expect(error.target_user).to eq(target) }
+    end
+
+    it "fails closed without attaching when the resolved account is suspended" do
+      target = create(:user)
+      target.add_role(:suspended)
+      payload = mlh_payload(uid: "core-switch-3", email: target.email)
+
+      expect do
+        expect do
+          described_class.call(payload, current_user: current_user)
+        end.to raise_error(Authentication::Errors::Ineligible)
+      end.not_to change(Identity, :count)
+    end
+  end
+
+  context "when the signed-in user resolves as the identity's owner themselves" do
+    it "attaches normally without requiring confirmation" do
+      payload = mlh_payload(uid: "core-self-1", email: current_user.email)
+
+      expect(described_class.call(payload, current_user: current_user)).to eq(current_user)
+      expect(current_user.identities.find_by(provider: "mlh").uid).to eq("core-self-1")
+    end
+  end
+
+  context "when the incoming unclaimed identity resolves to nobody" do
+    it "keeps the normal attach-to-current-user flow" do
+      payload = mlh_payload(uid: "core-nobody-1", email: "unclaimed@example.com")
+
+      expect do
+        expect(described_class.call(payload, current_user: current_user)).to eq(current_user)
+      end.to change(Identity, :count).by(1)
+    end
+  end
+end
diff --git a/spec/services/liquid_embed_extractor_spec.rb b/spec/services/liquid_embed_extractor_spec.rb
index 719a55eb6ab38..40abbc07178a4 100644
--- a/spec/services/liquid_embed_extractor_spec.rb
+++ b/spec/services/liquid_embed_extractor_spec.rb
@@ -74,8 +74,8 @@
     end
 
     it "correctly resolves internal DEV Article links wrapped in general UnifiedEmbeds into native polymorphic relationships" do
-      dev_article = create(:article, title: "Test Article")
-      dev_article.user.update!(username: "testuser")
+      user = create(:user, username: "testuser")
+      dev_article = create(:article, user: user, title: "Test Article")
       
       domain = Settings::General.app_domain || "localhost:3000"
       article_url = "http://#{domain}/testuser/#{dev_article.slug}"
diff --git a/vendor/cache/omniauth-mlh-4.1.0.gem b/vendor/cache/omniauth-mlh-4.1.0.gem
deleted file mode 100644
index 49a5ada30444e..0000000000000
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diff --git a/vendor/cache/omniauth-mlh-4.2.0.gem b/vendor/cache/omniauth-mlh-4.2.0.gem
new file mode 100644
index 0000000000000..32afc61464c53
Binary files /dev/null and b/vendor/cache/omniauth-mlh-4.2.0.gem differ