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

Re: Subresource Integrity and fingerprinting

From: Devdatta Akhawe <dev.akhawe@gmail.com>
Date: Wed, 8 Jan 2014 16:23:59 -0800
Message-ID: <CAPfop_1yHRXyhQOuePzc+nYjOsGevwS+=gsywCHXPkoa46hHXg@mail.gmail.com>
To: Michal Zalewski <lcamtuf@coredump.cx>
Cc: Joel Weinberger <jww@chromium.org>, Mike West <mkwst@google.com>, "public-webappsec@w3.org" <public-webappsec@w3.org>, Frederik Braun <fbraun@mozilla.com>
Hi

[separate thread for fingerprinting discussion]

> Also, to circle back to the fingerprinting angle: the logged-in state
> aside, let's say that there's a HTML page or a JSON response that is
> mostly static, except for a first name, e-mail address, or a phone
> number somewhere in the body. Further, for the sake of simplicity,
> let's say that it's cacheable on the client.

Exactly. That is definitely a concern. Personally, I think one
possible mitigation is:

The web platform guarantees (well, tries to) that HTML/JSON etc files
will be secret by default, while scripts/images/css have the weird
'run but not read' semantics. Maybe, integrity verification should
also follow this: sub-resource integrity verification only works
directly for files with an explicit mime-type that is for JS/CSS/img
etc. With our advocacy of code/data separation in CSP, I imagine there
could be lots of (small) JSON files with secret data that we don't
want leaking.

For all other cases (JSON/HTML files), we can require the relevant
Access-Control-Allow-Origin header whitelisting the current document
origin.

The more extreme version of this is to require the CORS headers for
all resources that go through integrity verification. But I believe
that is just throwing the baby out with the bathwater.

What do you think?

Thanks
Dev
Received on Thursday, 9 January 2014 00:24:46 UTC

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