W3C home > Mailing lists > Public > public-webappsec@w3.org > September 2014

Re: HTML Imports vs unsafe-inline

From: Mike West <mkwst@google.com>
Date: Thu, 11 Sep 2014 14:09:31 +0200
Message-ID: <CAKXHy=dBa2y_0dhQr9hKjURJG5e8CLT2vERNtjfcgLT-fWat-g@mail.gmail.com>
To: Jeffrey Yasskin <jyasskin@google.com>, Adam Barth <w3c@adambarth.com>
Cc: "public-webappsec@w3.org" <public-webappsec@w3.org>

Yes. Imports are weird.

I don't think there would be significant increase in risk to allow inline
scripts in an Import file, as you already need to whitelist the file itself
via 'script-src' (it's not clear to me how to express that clearly in spec
text, but that's hardly a concern worth considering).

I'm glad you suggested this, because it reminds me that I'm on the hook to
send a proposal to the list regarding the discussion on
https://crbug.com/393307, where Adam proposed a 'unsafe-static-inline'
source expression that allowed inline content from a non-script created
parser for exactly the Chrome Apps use case you're pointing out.

The idea is that the risk associated with 'unsafe-inline' is mitigated if
there's no dynamic content. Packaged resources could be considered "static"
in some sense, so the inline script risk would only come from DOM-based
injection, rather than raw inline injection via server-side bugs.

I think it's an interesting proposal, but one I'm reluctant to expose to
the web. Folks would fairly easily shoot themselves in the foot if they
were allowed to claim that a dynamic resource was static in the relevant


Mike West <mkwst@google.com>
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On Thu, Sep 11, 2014 at 6:19 AM, Jeffrey Yasskin <jyasskin@google.com>

> HTML Imports are a great way to import javascript, but the simple way
> to use them requires unsafe-inline:
> https://code.google.com/p/chromium/codesearch/#chromium/src/third_party/WebKit/Tools/GardeningServer/lib/update-util.html
> .
> It's possible to split each file in two, but that's inconvenient while
> editing and costs network requests. It's also possible to write a
> build step that generates hashes for each script, but injecting a
> build into the edit/debug cycle slows that cycle down.
> Is there something the CSP spec could do (either a new token or advice
> to authors) that would make these literal scripts easier to use
> without opening vulnerabilities?
> This is also relevant to Chrome Apps, which force a CSP to protect
> their users: https://developer.chrome.com/apps/contentSecurityPolicy.
> If there's something halfway to unsafe-inline that would still avoid
> the relevant vulnerabilities but would allow use of literal <script>
> tags, it'd be nice to let people use Polymer more easily.
> Unfortunately, I don't have a concrete suggestion here, partly because
> I don't understand the attacks that the inline-script restrictions are
> intended to defend against.
> Jeffrey
Received on Thursday, 11 September 2014 12:10:22 UTC

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