diff --git a/app/models/article.rb b/app/models/article.rb
index 1cea1c313..170790af6 100644
--- a/app/models/article.rb
+++ b/app/models/article.rb
@@ -32,6 +32,7 @@ class Article < ApplicationRecord
   MAX_USER_MENTION_LIVE_AT = Time.utc(2021, 4, 7).freeze
   UNIQUE_URL_ERROR = "has already been taken. " \
                      "Email #{ForemInstance.email} for further details.".freeze
+  PROHIBITED_UNICODE_CHARACTERS_REGEX = /[\u202a-\u202e]/ # BIDI embedding controls
 
   has_one :discussion_lock, dependent: :delete
 
@@ -81,7 +82,6 @@ class Article < ApplicationRecord
   validates :slug, presence: { if: :published? }, format: /\A[0-9a-z\-_]*\z/
   validates :slug, uniqueness: { scope: :user_id }
   validates :title, presence: true, length: { maximum: 128 }
-  validates :user_id, presence: true
   validates :user_subscriptions_count, presence: true
   validates :video, url: { allow_blank: true, schemes: %w[https http] }
   validates :video_closed_caption_track_url, url: { allow_blank: true, schemes: ["https"] }
@@ -101,6 +101,7 @@ class Article < ApplicationRecord
   validate :validate_co_authors_exist, unless: -> { co_author_ids.blank? }
 
   before_validation :evaluate_markdown, :create_slug
+  before_validation :remove_prohibited_unicode_characters
   before_save :update_cached_user
   before_save :set_all_dates
 
@@ -847,4 +848,10 @@ class Article < ApplicationRecord
 
     ::Articles::EnrichImageAttributesWorker.perform_async(id)
   end
+
+  def remove_prohibited_unicode_characters
+    return unless title&.match?(PROHIBITED_UNICODE_CHARACTERS_REGEX)
+
+    self.title = title.gsub(PROHIBITED_UNICODE_CHARACTERS_REGEX, "")
+  end
 end
diff --git a/app/models/tag.rb b/app/models/tag.rb
index 7fe324c6b..967cd7b7f 100644
--- a/app/models/tag.rb
+++ b/app/models/tag.rb
@@ -77,7 +77,7 @@ class Tag < ActsAsTaggableOn::Tag
     # [:alnum:] is not used here because it supports diacritical characters.
     # If we decide to allow diacritics in the future, we should replace the
     # following regex with [:alnum:].
-    errors.add(:name, "contains non-alphanumeric characters") unless name.match?(/\A[[:alnum:]]+\z/i)
+    errors.add(:name, I18n.t("errors.messages.contains_prohibited_characters")) unless name.match?(/\A[[:alnum:]]+\z/i)
   end
 
   def errors_as_sentence
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 2f2486504..3d5fbb08f 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -140,6 +140,7 @@ en:
       bad_uri: is an invalid url
       blank: can't be blank
       confirmation: doesn't match %{attribute}
+      contains_prohibited_characters: contains non-alphanumeric or prohibited unicode characters
       empty: can't be empty
       equal_to: must be equal to %{count}
       even: must be even
diff --git a/config/locales/fr.yml b/config/locales/fr.yml
index 287ef18c2..372a61661 100644
--- a/config/locales/fr.yml
+++ b/config/locales/fr.yml
@@ -157,6 +157,7 @@ fr:
       blank: ne peut pas être vide
       confirmation: ne correspond pas à %{attribute}
       confirmation_period_expired: doit être confirmé dans %{period}, veuillez en demander un nouveau
+      contains_prohibited_characters: contient des caractères unicode non alphanumériques ou interdits
       empty: ne peut pas être vide
       equal_to: doit être égal à %{count}
       even: doit être pair
diff --git a/spec/models/article_spec.rb b/spec/models/article_spec.rb
index d9bea1e29..87c351a94 100644
--- a/spec/models/article_spec.rb
+++ b/spec/models/article_spec.rb
@@ -47,7 +47,6 @@ RSpec.describe Article, type: :model do
     it { is_expected.to validate_presence_of(:reactions_count) }
     it { is_expected.to validate_presence_of(:user_subscriptions_count) }
     it { is_expected.to validate_presence_of(:title) }
-    it { is_expected.to validate_presence_of(:user_id) }
 
     it { is_expected.to validate_uniqueness_of(:slug).scoped_to(:user_id) }
 
@@ -233,6 +232,34 @@ RSpec.describe Article, type: :model do
       end
     end
 
+    describe "title validation" do
+      it "produces a proper title" do
+        test_article = build(:article, title: "An Article Title")
+
+        test_article.validate
+
+        expect(test_article.title).to eq("An Article Title")
+      end
+
+      it "sanitizes the title" do
+        test_article = build(:article, title: "\u202dThis starts with BIDI override")
+
+        test_article.validate
+
+        expect(test_article.title).not_to match(/\u202d/)
+        expect(test_article.title).to eq("This starts with BIDI override")
+      end
+
+      it "rejects empty titles after sanitizing" do
+        test_article = build(:article, title: "\u202a\u202b\u202c\u202d\u202e")
+
+        test_article.validate
+
+        expect(test_article).not_to be_valid
+        expect(test_article.errors_as_sentence).to match("Title can't be blank")
+      end
+    end
+
     describe "tag validation" do
       let(:article) { build(:article, user: user) }
 
diff --git a/spec/models/tag_spec.rb b/spec/models/tag_spec.rb
index bcc14a811..81acf6ad0 100644
--- a/spec/models/tag_spec.rb
+++ b/spec/models/tag_spec.rb
@@ -86,6 +86,11 @@ RSpec.describe Tag, type: :model do
       end
     end
 
+    it "fails validation if name is a prohibited (whitespace) unicode character" do
+      tag.name = "U+202D"
+      expect(tag).not_to be_valid
+    end
+
     describe "alias_for" do
       it "passes validation if the alias refers to an existing tag" do
         tag = create(:tag)