discourse/lib/onebox/sanitize_config.rb

# frozen_string_literal: true

module Onebox
  module SanitizeConfig
    HTTP_PROTOCOLS ||= ['http', 'https', :relative].freeze

    ONEBOX ||= Sanitize::Config.freeze_config(Sanitize::Config.merge(Sanitize::Config::RELAXED,
      elements: Sanitize::Config::RELAXED[:elements] + %w[audio details embed iframe source video svg path],

      attributes: {
        'a' => Sanitize::Config::RELAXED[:attributes]['a'] + %w(target),
        'audio' => %w[controls controlslist],
        'embed' => %w[height src type width],
        'iframe' => %w[allowfullscreen frameborder height scrolling src width data-original-href data-unsanitized-src],
        'source' => %w[src type],
        'video' => %w[controls height loop width autoplay muted poster controlslist playsinline],
        'path' => %w[d],
        'svg' => ['aria-hidden', 'width', 'height', 'viewbox'],
        'div' => [:data], # any data-* attributes,
        'span' => [:data], # any data-* attributes
      },

      add_attributes: {
        'iframe' => {
          'seamless' => 'seamless',
          'sandbox' => 'allow-same-origin allow-scripts allow-forms allow-popups allow-popups-to-escape-sandbox' \
                       ' allow-presentation',
        }
      },

      transformers: (Sanitize::Config::RELAXED[:transformers] || []) + [
        lambda do |env|
          next unless env[:node_name] == 'a'
          a_tag = env[:node]
          a_tag['href'] ||= '#'
          if a_tag['href'] =~ %r{^(?:[a-z]+:)?//}
            a_tag['rel'] = 'nofollow ugc noopener'
          else
            a_tag.remove_attribute('target')
          end
        end,

        lambda do |env|
          next unless env[:node_name] == 'iframe'

          iframe = env[:node]
          allowed_regexes = env[:config][:allowed_iframe_regexes] || [/.*/]

          allowed = allowed_regexes.any? { |r| iframe["src"] =~ r }

          if !allowed
            # add a data attribute with the blocked src. This is not required
            # but makes it much easier to troubleshoot onebox issues
            iframe["data-unsanitized-src"] = iframe["src"]
            iframe.remove_attribute("src")
          end
        end
      ],

      protocols: {
        'embed' => { 'src' => HTTP_PROTOCOLS },
        'iframe' => { 'src' => HTTP_PROTOCOLS },
        'source' => { 'src' => HTTP_PROTOCOLS },
      },

      css: {
        properties: Sanitize::Config::RELAXED[:css][:properties] + %w[--aspect-ratio]
      }
    ))

    DISCOURSE_ONEBOX ||=
      Sanitize::Config.freeze_config(
        Sanitize::Config.merge(
          ONEBOX,
          attributes: Sanitize::Config.merge(
            ONEBOX[:attributes],
            'aside' => [:data]
          )
        )
      )
  end
end