SECURITY: Limit email invitations to topic

app/models/invite.rb

@@ -115,6 +115,8 @@ class Invite < ActiveRecord::Base
         invite.destroy
         invite = nil
       end
+      email_digest = Digest::SHA256.hexdigest(email)
+      RateLimiter.new(invited_by, "reinvites-per-day-#{email_digest}", 3, 1.day.to_i).performed!
     end
 
     emailed_status = if opts[:skip_email] || invite&.emailed_status == emailed_status_types[:not_required]

spec/models/invite_spec.rb

@@ -181,6 +181,24 @@ describe Invite do
 
         expect(invite.invite_key).not_to eq(another_invite.invite_key)
       end
+
+      context "when email is already invited 3 times" do
+        before do
+          RateLimiter.enable
+          3.times do
+            Invite.generate(user, email: "test@example.com")
+          end
+        end
+
+        after do
+          RateLimiter.clear_all!
+        end
+
+        it "raises an error" do
+          expect { Invite.generate(user, email: "test@example.com") }
+            .to raise_error(RateLimiter::LimitExceeded)
+        end
+      end
     end
 
     context 'invite to a topic' do