diff --git a/app/controllers/concerns/signature_verification.rb b/app/controllers/concerns/signature_verification.rb
index 5f95fa3461f..e5d5e2ca619 100644
--- a/app/controllers/concerns/signature_verification.rb
+++ b/app/controllers/concerns/signature_verification.rb
@@ -22,6 +22,12 @@ module SignatureVerification
       return
     end
 
+    if request.headers['Date'].present? && !matches_time_window?
+      @signature_verification_failure_reason = 'Signed request date outside acceptable time window'
+      @signed_request_account = nil
+      return
+    end
+
     raw_signature    = request.headers['Signature']
     signature_params = {}
 
@@ -76,7 +82,7 @@ module SignatureVerification
   def build_signed_string(signed_headers)
     signed_headers = 'date' if signed_headers.blank?
 
-    signed_headers.split(' ').map do |signed_header|
+    signed_headers.downcase.split(' ').map do |signed_header|
       if signed_header == Request::REQUEST_TARGET
         "#{Request::REQUEST_TARGET}: #{request.method.downcase} #{request.path}"
       elsif signed_header == 'digest'
@@ -87,6 +93,16 @@ module SignatureVerification
     end.join("\n")
   end
 
+  def matches_time_window?
+    begin
+      time_sent = Time.httpdate(request.headers['Date'])
+    rescue ArgumentError
+      return false
+    end
+
+    (Time.now.utc - time_sent).abs <= 12.hours
+  end
+
   def body_digest
     "SHA-256=#{Digest::SHA256.base64digest(request_body)}"
   end
diff --git a/app/lib/formatter.rb b/app/lib/formatter.rb
index 8b694536c24..35d5a09b766 100644
--- a/app/lib/formatter.rb
+++ b/app/lib/formatter.rb
@@ -90,8 +90,12 @@ class Formatter
 
   private
 
+  def html_entities
+    @html_entities ||= HTMLEntities.new
+  end
+
   def encode(html)
-    HTMLEntities.new.encode(html)
+    html_entities.encode(html)
   end
 
   def encode_and_link_urls(html, accounts = nil, options = {})
@@ -143,7 +147,7 @@ class Formatter
         emoji     = emoji_map[shortcode]
 
         if emoji
-          replacement = "<img draggable=\"false\" class=\"emojione\" alt=\":#{shortcode}:\" title=\":#{shortcode}:\" src=\"#{emoji}\" />"
+          replacement = "<img draggable=\"false\" class=\"emojione\" alt=\":#{encode(shortcode)}:\" title=\":#{encode(shortcode)}:\" src=\"#{encode(emoji)}\" />"
           before_html = shortname_start_index.positive? ? html[0..shortname_start_index - 1] : ''
           html        = before_html + replacement + html[i + 1..-1]
           i          += replacement.size - (shortcode.size + 2) - 1
@@ -212,7 +216,7 @@ class Formatter
     return link_to_account(acct) unless linkable_accounts
 
     account = linkable_accounts.find { |item| TagManager.instance.same_acct?(item.acct, acct) }
-    account ? mention_html(account) : "@#{acct}"
+    account ? mention_html(account) : "@#{encode(acct)}"
   end
 
   def link_to_account(acct)
@@ -221,7 +225,7 @@ class Formatter
     domain  = nil if TagManager.instance.local_domain?(domain)
     account = EntityCache.instance.mention(username, domain)
 
-    account ? mention_html(account) : "@#{acct}"
+    account ? mention_html(account) : "@#{encode(acct)}"
   end
 
   def link_to_hashtag(entity)
@@ -239,10 +243,10 @@ class Formatter
   end
 
   def hashtag_html(tag)
-    "<a href=\"#{tag_url(tag.downcase)}\" class=\"mention hashtag\" rel=\"tag\">#<span>#{tag}</span></a>"
+    "<a href=\"#{encode(tag_url(tag.downcase))}\" class=\"mention hashtag\" rel=\"tag\">#<span>#{encode(tag)}</span></a>"
   end
 
   def mention_html(account)
-    "<span class=\"h-card\"><a href=\"#{TagManager.instance.url_for(account)}\" class=\"u-url mention\">@<span>#{account.username}</span></a></span>"
+    "<span class=\"h-card\"><a href=\"#{encode(TagManager.instance.url_for(account))}\" class=\"u-url mention\">@<span>#{encode(account.username)}</span></a></span>"
   end
 end
diff --git a/spec/controllers/concerns/signature_verification_spec.rb b/spec/controllers/concerns/signature_verification_spec.rb
index 3daf1fc4e8c..72069009716 100644
--- a/spec/controllers/concerns/signature_verification_spec.rb
+++ b/spec/controllers/concerns/signature_verification_spec.rb
@@ -73,6 +73,30 @@ describe ApplicationController, type: :controller do
       end
     end
 
+    context 'with request older than a day' do
+      before do
+        get :success
+
+        fake_request = Request.new(:get, request.url)
+        fake_request.add_headers({ 'Date' => 2.days.ago.utc.httpdate })
+        fake_request.on_behalf_of(author)
+
+        request.headers.merge!(fake_request.headers)
+      end
+
+      describe '#signed_request?' do
+        it 'returns true' do
+          expect(controller.signed_request?).to be true
+        end
+      end
+
+      describe '#signed_request_account' do
+        it 'returns nil' do
+          expect(controller.signed_request_account).to be_nil
+        end
+      end
+    end
+
     context 'with body' do
       before do
         post :success, body: 'Hello world'