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

Re: [CSP] different perspective on Report-Only

From: Martin Thomson <martin.thomson@gmail.com>
Date: Sat, 27 Dec 2014 20:42:35 -0800
Message-ID: <CABkgnnWrB1d6F4K1dmFjyjj0oZMxLFez5fWJf+siH8AW-rvAHA@mail.gmail.com>
To: "Ludwig, Sven" <Sven.Ludwig@senacor.com>
Cc: "public-webappsec@w3.org" <public-webappsec@w3.org>
Perhaps the right interpretation is "report to no-one but X".  That
would cause two conflicting directives to turn into "don't report to
anyone".

(If you think of each directive as narrowing scope, then logically the
absence of a -report-only directive is to report to everyone, but I
think we can handle that.)

On 26 December 2014 at 17:40, Ludwig, Sven <Sven.Ludwig@senacor.com> wrote:
> Hi,
>
>
>
> following the excellent talk https://www.youtube.com/watch?v=pocsv39pNXA by
> Adam Barth, CSP supports setting multiple policies (i.e. multiple
> Content-Security-Policy headers) in a response, which then all must be
> fulfilled. One reason for this principle as mentioned in the talk is that an
> attacker might somehow be able to add his own CSP header to the response,
> however without replacing existing headers coming from the server. In this
> case the attack does not open up security, because additional
> Content-Security-Policy headers can only introduce more restrictions.
>
>
>
> Having said that, the header Content-Security-Policy-Report-Only could be
> considered by an attacker to add, to open up security.
>
>
>
> Right now I am not sure if this could be an issue.
>
>
>
> If any Content-Security-Policy headers have precedence over any
> Content-Security-Policy-Report-Only headers, the attacker would still not be
> able to open up security in the above mentioned way. Actually, I expect it
> to work like that. This should be mentioned in the section
> http://www.w3.org/TR/CSP2/#content-security-policy-report-only
>
>
>
> Kind Regards,
>
> Sven
>
>
>
>
>
> Sven Ludwig
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Received on Sunday, 28 December 2014 04:43:13 UTC

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