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Sanitize and sandbox toot embeds #9552

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Dec 23, 2018
Merged

Sanitize and sandbox toot embeds #9552

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1 change: 1 addition & 0 deletions app/controllers/api/web/embeds_controller.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,7 @@ def create
render json: status, serializer: OEmbedSerializer, width: 400
rescue ActiveRecord::RecordNotFound
oembed = FetchOEmbedService.new.call(params[:url])
oembed[:html] = Formatter.instance.sanitize(oembed[:html], Sanitize::Config::MASTODON_OEMBED) if oembed[:html].present?
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This will break Mastodon embeds because they need a <script> for iframe resizing, and this ruleset strips out script tags.

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As I said:

This does cause some functionality loss: the generated code for embedding remote toots will not include the JS snippet needed to adjust the iframe's height.

But I prefer that to instructing users to include untrusted code (note that embeds from your own instance don't go through that codepath and the javascript tag is still included).

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What I mean is, it's okayish to instruct people to include scripts that we control, but I don't think it's ok at all to instruct them to include scripts from a remote instance we don't control.


if oembed
render json: oembed
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1 change: 1 addition & 0 deletions app/javascript/mastodon/features/ui/components/embed_modal.js
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Expand Up @@ -77,6 +77,7 @@ class EmbedModal extends ImmutablePureComponent {
className='embed-modal__iframe'
frameBorder='0'
ref={this.setIframeRef}
sandbox='allow-same-origin'
title='preview'
/>
</div>
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