chore(main): release 3.3.6 (#3558)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

.gitignore

@@ -34,3 +34,6 @@ BRANCH
 .rubocop-https*
 .env*
 
+node_modules
+yarn.lock
+

.release-please-manifest.json

@@ -1,3 +1,3 @@
 {
-  ".": "3.3.5"
+  ".": "3.3.6"
 }

CHANGELOG.md

@@ -2,6 +2,25 @@
 
 This file contains all the latest changes and updates to Postal.
 
+## [3.3.6](https://github.com/postalserver/postal/compare/3.3.5...3.3.6) (2026-04-28)
+
+
+### Bug Fixes
+
+* **messages:** sandbox rendered email HTML as extra XSS defence ([cad2aa6](https://github.com/postalserver/postal/commit/cad2aa6808519a3ff25215f09f4966d9fa3bb372))
+
+
+### Miscellaneous Chores
+
+* ignore node modules and yarn.lock ([b611d57](https://github.com/postalserver/postal/commit/b611d577af79b8e1e75b6d47fa04d1ba03e34eec))
+
+
+### Code Refactoring
+
+* **auth:** tighten return_to validation ([84f4e20](https://github.com/postalserver/postal/commit/84f4e20f05db2d11b0144f95960c956f8221e657))
+* **helpers:** escape interpolated values in select options ([9243524](https://github.com/postalserver/postal/commit/924352403553dcfcc569876ca76c219493fac9d6))
+* **tracking:** remove unused src image proxy ([dca7f90](https://github.com/postalserver/postal/commit/dca7f90b9046247c0d953567be35921167e79d87))
+
 ## [3.3.5](https://github.com/postalserver/postal/compare/3.3.4...3.3.5) (2026-02-01)
 
 

Gemfile.lock

@@ -123,7 +123,7 @@ GEM
     dynamic_form (1.2.0)
     email_validator (2.2.4)
       activemodel
-    erb (6.0.1.1)
+    erb (5.0.2)
     erubi (1.12.0)
     execjs (2.7.0)
     factory_bot (6.4.6)

app/controllers/application_controller.rb

@@ -62,10 +62,13 @@ class ApplicationController < ActionController::Base
   end
 
   def url_with_return_to(url)
-    if params[:return_to].blank? || !params[:return_to].starts_with?("/")
+    return_to = params[:return_to]
+    if return_to.blank? ||
+       !return_to.start_with?("/") ||
+       return_to.start_with?("//", "/\\")
       url_for(url)
     else
-      params[:return_to]
+      return_to
     end
   end
 

app/controllers/messages_controller.rb

@@ -89,6 +89,18 @@ class MessagesController < ApplicationController
   end
 
   def html_raw
+    override_content_security_policy_directives(
+      default_src: %w('none'),
+      script_src: %w('none'),
+      style_src: %w('unsafe-inline'),
+      img_src: %w(* data:),
+      font_src: %w(*),
+      frame_ancestors: %w('self'),
+      form_action: %w('none'),
+      base_uri: %w('none')
+    )
+    response.headers["X-Content-Type-Options"] = "nosniff"
+    response.headers["Referrer-Policy"] = "no-referrer"
     render html: @message.html_body_without_tracking_image.html_safe
   end
 

app/helpers/application_helper.rb

@@ -33,7 +33,7 @@ module ApplicationHelper
         s << "<optgroup label='Server Domains'>"
         server_domains.each do |domain|
           selected = domain == selected_domain ? "selected='selected'" : ""
-          s << "<option value='#{domain.id}' #{selected}>#{domain.name}</option>"
+          s << "<option value='#{h(domain.id)}' #{selected}>#{h(domain.name)}</option>"
         end
         s << "</optgroup>"
       end
@@ -43,7 +43,7 @@ module ApplicationHelper
         s << "<optgroup label='Organization Domains'>"
         organization_domains.each do |domain|
           selected = domain == selected_domain ? "selected='selected'" : ""
-          s << "<option value='#{domain.id}' #{selected}>#{domain.name}</option>"
+          s << "<option value='#{h(domain.id)}' #{selected}>#{h(domain.name)}</option>"
         end
         s << "</optgroup>"
       end
@@ -60,7 +60,7 @@ module ApplicationHelper
         http_endpoints.each do |endpoint|
           value = "#{endpoint.class}##{endpoint.uuid}"
           selected = value == selected_value ? "selected='selected'" : ""
-          s << "<option value='#{value}' #{selected}>#{endpoint.description}</option>"
+          s << "<option value='#{h(value)}' #{selected}>#{h(endpoint.description)}</option>"
         end
         s << "</optgroup>"
       end
@@ -71,7 +71,7 @@ module ApplicationHelper
         smtp_endpoints.each do |endpoint|
           value = "#{endpoint.class}##{endpoint.uuid}"
           selected = value == selected_value ? "selected='selected'" : ""
-          s << "<option value='#{value}' #{selected}>#{endpoint.description}</option>"
+          s << "<option value='#{h(value)}' #{selected}>#{h(endpoint.description)}</option>"
         end
         s << "</optgroup>"
       end
@@ -82,7 +82,7 @@ module ApplicationHelper
         address_endpoints.each do |endpoint|
           value = "#{endpoint.class}##{endpoint.uuid}"
           selected = value == selected_value ? "selected='selected'" : ""
-          s << "<option value='#{value}' #{selected}>#{endpoint.address}</option>"
+          s << "<option value='#{h(value)}' #{selected}>#{h(endpoint.address)}</option>"
         end
         s << "</optgroup>"
       end
@@ -94,7 +94,7 @@ module ApplicationHelper
 
           selected = (selected_value == mode ? "selected='selected'" : "")
           text = t("route_modes.#{mode.underscore}")
-          s << "<option value='#{mode}' #{selected}>#{text}</option>"
+          s << "<option value='#{h(mode)}' #{selected}>#{h(text)}</option>"
         end
         s << "</optgroup>"
       end

app/views/messages/html.html.haml

@@ -14,4 +14,4 @@
         This means that we no longer store the raw data for this e-mail
         or the e-mail didn't include a HTML part.
 - else
-  %iframe{:width => "100%", :height => "100%", :src => html_raw_organization_server_message_path(organization, @server, @message.id)}
+  %iframe{:width => "100%", :height => "100%", :sandbox => "allow-popups allow-popups-to-escape-sandbox", :referrerpolicy => "no-referrer", :src => html_raw_organization_server_message_path(organization, @server, @message.id)}

lib/tracking_middleware.rb

@@ -48,25 +48,11 @@ class TrackingMiddleware
       Sentry.capture_exception(e) if defined?(Sentry)
     end
 
-    source_image = request.params["src"]
-    case source_image
-    when nil
+    if request.params["src"].nil?
       headers = {}
       headers["Content-Type"] = "image/png"
       headers["Content-Length"] = TRACKING_PIXEL.bytesize.to_s
       [200, headers, [TRACKING_PIXEL]]
-    when /\Ahttps?:\/\//
-      response = Postal::HTTP.get(source_image, timeout: 3)
-      return [404, {}, ["Not found"]] unless response[:code] == 200
-
-      headers = {}
-      headers["Content-Type"] = response[:headers]["content-type"]&.first
-      headers["Last-Modified"] = response[:headers]["last-modified"]&.first
-      headers["Cache-Control"] = response[:headers]["cache-control"]&.first
-      headers["Etag"] = response[:headers]["etag"]&.first
-      headers["Content-Length"] = response[:body].bytesize.to_s
-      [200, headers, [response[:body]]]
-
     else
       [400, {}, ["Invalid/missing source image"]]
     end

spec/helpers/application_helper_spec.rb

@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+require "rails_helper"
+
+RSpec.describe ApplicationHelper, type: :helper do
+  describe "#endpoint_options_for_select" do
+    let(:server) { create(:server) }
+
+    context "when an endpoint has HTML characters in its description" do
+      let(:payload) { %q(x'"><script>alert(1)</script>) }
+
+      before do
+        create(:http_endpoint, server: server, name: payload)
+      end
+
+      it "HTML-escapes the endpoint description in the option text" do
+        html = helper.endpoint_options_for_select(server)
+
+        # The raw payload must not appear verbatim — if it does, the browser
+        # will execute the <script> tag.
+        expect(html).not_to include("<script>alert(1)</script>")
+
+        # Escaped form should appear instead.
+        expect(html).to include("&lt;script&gt;alert(1)&lt;/script&gt;")
+      end
+
+      it "does not allow the payload to break out of the option tag" do
+        html = helper.endpoint_options_for_select(server)
+
+        # The ' and > characters in the payload must be escaped so they
+        # cannot close the opening <option value='...'> or terminate the
+        # element early.
+        expect(html).not_to match(/<option[^>]*>[^<]*<script/)
+      end
+    end
+  end
+end

spec/lib/tracking_middleware_spec.rb

@@ -0,0 +1,71 @@
+# frozen_string_literal: true
+
+require "rails_helper"
+require "rack/test"
+
+RSpec.describe TrackingMiddleware do
+  include Rack::Test::Methods
+
+  let(:inner_app) { ->(_env) { [200, {}, ["inner"]] } }
+  let(:app) { described_class.new(inner_app) }
+
+  let(:server) { create(:server) }
+  let(:message) do
+    MessageFactory.incoming(server) do |_msg, mail|
+      mail.html_part = Mail::Part.new do
+        content_type "text/html; charset=UTF-8"
+        body "<html><body>hi</body></html>"
+      end
+    end
+  end
+
+  def track_headers
+    { "HTTP_X_POSTAL_TRACK_HOST" => "1" }
+  end
+
+  describe "GET /img/:server_token/:message_token (open tracking pixel)" do
+    before do
+      get "/img/#{server.token}/#{message.token}", {}, track_headers
+    end
+
+    it "returns the tracking pixel PNG" do
+      expect(last_response.status).to eq 200
+      expect(last_response.headers["Content-Type"]).to eq "image/png"
+      expect(last_response.body.bytesize).to be > 0
+    end
+
+    it "records a load for the message" do
+      # Re-fetch the message so loads are read fresh from the DB.
+      reloaded = server.message_db.message(message.id)
+      expect(reloaded.loads.size).to eq 1
+    end
+  end
+
+  describe "GET /img/:server_token/:message_token?src=<url> (image proxy)" do
+    let(:attacker_url) { "http://internal.example.com/secret" }
+
+    before do
+      stub_request(:get, attacker_url).to_return(status: 200, body: "internal-secret")
+    end
+
+    it "does not fetch the URL and returns 400" do
+      get "/img/#{server.token}/#{message.token}", { src: attacker_url }, track_headers
+
+      expect(last_response.status).to eq 400
+      expect(WebMock).not_to have_requested(:get, attacker_url)
+    end
+
+    it "does not fetch the URL even when the message token is invalid" do
+      get "/img/#{server.token}/nonexistent", { src: attacker_url }, track_headers
+
+      expect(WebMock).not_to have_requested(:get, attacker_url)
+    end
+  end
+
+  describe "when the track-host header is missing" do
+    it "passes the request through to the inner app untouched" do
+      get "/img/#{server.token}/#{message.token}"
+      expect(last_response.body).to eq "inner"
+    end
+  end
+end

spec/rails_helper.rb

@@ -16,7 +16,7 @@ require "shoulda-matchers"
 DatabaseCleaner.allow_remote_database_url = true
 ActiveRecord::Base.logger = Logger.new("/dev/null")
 
-Dir[File.expand_path("helpers/**/*.rb", __dir__)].each { |f| require f }
+Dir[File.expand_path("helpers/**/*.rb", __dir__)].reject { |f| f.end_with?("_spec.rb") }.each { |f| require f }
 
 ActionMailer::Base.delivery_method = :test
 

spec/requests/messages_controller_spec.rb

@@ -0,0 +1,58 @@
+# frozen_string_literal: true
+
+require "rails_helper"
+
+RSpec.describe "MessagesController", type: :request do
+  let(:user) { create(:user, admin: true) }
+  let(:organization) { create(:organization, owner: user) }
+  let(:server) { create(:server, organization: organization) }
+
+  before do
+    post "/login", params: { email_address: user.email_address, password: "passw0rd" }
+  end
+
+  describe "GET /org/:org/servers/:server/messages/:id/html_raw" do
+    let(:xss_payload) { %(<script>alert("XSS")</script>) }
+    let(:message) do
+      payload = xss_payload
+      MessageFactory.incoming(server) do |_msg, mail|
+        mail.html_part = Mail::Part.new do
+          content_type "text/html; charset=UTF-8"
+          body %(<html><body><p>hello</p>#{payload}</body></html>)
+        end
+      end
+    end
+
+    before do
+      get "/org/#{organization.permalink}/servers/#{server.permalink}/messages/#{message.id}/html_raw"
+    end
+
+    it "returns the stored email HTML" do
+      expect(response).to have_http_status(:ok)
+      expect(response.body).to include("hello")
+    end
+
+    it "serves a restrictive Content-Security-Policy that blocks scripts" do
+      csp = response.headers["Content-Security-Policy"]
+      expect(csp).to include("script-src 'none'")
+      expect(csp).to include("default-src 'none'")
+      expect(csp).to include("form-action 'none'")
+      expect(csp).to include("base-uri 'none'")
+    end
+
+    it "sets X-Content-Type-Options and Referrer-Policy on the response" do
+      expect(response.headers["X-Content-Type-Options"]).to eq "nosniff"
+      expect(response.headers["Referrer-Policy"]).to eq "no-referrer"
+    end
+  end
+
+  describe "messages/html view template" do
+    # We assert against the template source rather than rendering it in a
+    # request spec because the full application layout depends on the asset
+    # pipeline which is not configured in this test environment.
+    it "embeds the html_raw view inside a sandboxed iframe" do
+      template = Rails.root.join("app/views/messages/html.html.haml").read
+      expect(template).to match(/%iframe\{[^}]*:sandbox\s*=>/)
+    end
+  end
+end

spec/requests/sessions_controller_spec.rb

@@ -0,0 +1,71 @@
+# frozen_string_literal: true
+
+require "rails_helper"
+
+RSpec.describe "SessionsController", type: :request do
+  let(:user) { create(:user) }
+
+  describe "POST /login with return_to" do
+    def login_with(return_to:)
+      post "/login", params: {
+        email_address: user.email_address,
+        password: "passw0rd",
+        return_to: return_to
+      }
+    end
+
+    shared_examples "rejects unsafe return_to" do
+      it "does not redirect to the attacker-controlled location" do
+        login_with(return_to: unsafe_path)
+
+        expect(response).to have_http_status(:found)
+        # Whatever the fallback is, it must be same-origin: a Location that
+        # either omits a host or points at our own host. A browser must not
+        # end up at attacker.example.
+        location = response.location
+        expect(location).not_to include("attacker.example")
+        # Reject protocol-relative and absolute redirects entirely.
+        expect(location).not_to match(%r{\A//})
+        expect(location).not_to match(%r{\Ahttps?://attacker})
+      end
+    end
+
+    context "with a protocol-relative URL (//host)" do
+      let(:unsafe_path) { "//attacker.example/phish" }
+      include_examples "rejects unsafe return_to"
+    end
+
+    context "with a backslash-prefixed URL (/\\host)" do
+      let(:unsafe_path) { "/\\attacker.example/phish" }
+      include_examples "rejects unsafe return_to"
+    end
+
+    context "with an absolute http(s) URL" do
+      let(:unsafe_path) { "https://attacker.example/phish" }
+      include_examples "rejects unsafe return_to"
+    end
+
+    context "with a javascript: URL" do
+      let(:unsafe_path) { "javascript:alert(1)" }
+      include_examples "rejects unsafe return_to"
+    end
+
+    context "with a safe relative path" do
+      it "honours the return_to" do
+        login_with(return_to: "/org/acme/settings")
+        expect(response).to redirect_to("/org/acme/settings")
+      end
+    end
+
+    context "with no return_to" do
+      it "redirects to the default root" do
+        post "/login", params: {
+          email_address: user.email_address,
+          password: "passw0rd"
+        }
+        expect(response).to have_http_status(:found)
+        expect(response.location).not_to match(%r{\A//})
+      end
+    end
+  end
+end