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Re: [CSP] Extensions and user script? (Some feedback)

From: Eric Chen <eric.chen@sv.cmu.edu>
Date: Wed, 29 Aug 2012 10:29:03 -0700
Message-ID: <CAF8haaytMdevN61dOvKLu-tz-RBCcC2gSHkJn5EzDBwt_GAnsQ@mail.gmail.com>
To: Odin HÝrthe Omdal <odinho@opera.com>
Cc: "public-webappsec@w3.org" <public-webappsec@w3.org>
I'm not sure if this idea has been discussed before, but why not have a CSP
policy that disables extensions? Disabling extensions entirely is probably
better than half-breaking extensions.


On Wed, Aug 29, 2012 at 4:34 AM, Odin HÝrthe Omdal <odinho@opera.com> wrote:

> Hello all :-)
> I've gotten some internal web site author feedback trying to implement CSP
> on a web email service that I'd like to share and discuss.
> There's of course a few minor things that will get better with time. Like
> browsers using prefixes and different implementations of different
> versions of the spec. As well as some potential bugs found, such as using
> an same-domain iframe with an email in it, and then rewriting links
> therein to do target=_blank, and it was suddenly blocked. They had to open
> up frame-src: * in order for the links to open. From my cursory reading of
> the spec, it does seem like this is in fact intended behaviour, but I'm
> not sure.
> The biggest problem however is the interference of pages' CSP policies
> when an extension goes mucking around the page doing whatever it likes to
> do.
> This is not the same as having a CSP-profile on the extension, as Chrome
> is doing, but the other way around:
>  Extensions can
>> inject arbitrary javascript, css into the page and modify the DOM in any
>> way. Depending on the CSP policy, those will potentially be blocked. The
>> most annoying thing is that those might break your extension or the page
>> in subtle ways because some things the extension does work (DOM
>> manipulations), but other things fail (scripts/css injection).
>> Additionally changes that do fail will generate heaps of false positive
>> feedback reports, making the reporting feature a pain to sift through
>> and work out "now is this a problem with my CSP poilicy, or is it some
>> extension the users installed that's trying to modify the page in some
>> way".
>> I don't see any realistic solution to this. You'd have to track a whole
>> bunch of manipulations and changes to the DOM as either "done by the
>> page" or "done by an extension" to work out if they should be allowed or
>> not.
>> So at first I thought "what a great idea", but after two days of messing
>> around and actually trying to use it, I decided that it might be
>> bordering on unuseable in the real world
> I have not looked into it myself, but this is a very valid concern if we
> were to implement it in Opera. What have you that have implemented this
> already done about it? How does it work? Is really extensions crippled in
> such a way, do they have to think about it?
> --
> Odin HÝrthe Omdal (Velmont/odinho) ∑ Core, Opera Software,
> http://opera.com
Received on Wednesday, 29 August 2012 17:29:31 UTC

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