W3C home > Mailing lists > Public > public-webappsec@w3.org > July 2015

Re: CSP2: Drop 'unsafe-redirect'.

From: Anne van Kesteren <annevk@annevk.nl>
Date: Thu, 2 Jul 2015 12:03:32 +0200
Message-ID: <CADnb78ha+gU4J9MszWqt821Zum-UxaU3S85A7TVZ3GGeamXg-g@mail.gmail.com>
To: Mike West <mkwst@google.com>
Cc: Brian Smith <brian@briansmith.org>, "public-webappsec@w3.org" <public-webappsec@w3.org>, Wendy Seltzer <wseltzer@w3.org>, Brad Hill <hillbrad@gmail.com>, Dan Veditz <dveditz@mozilla.com>
On Thu, Jul 2, 2015 at 11:39 AM, Mike West <mkwst@google.com> wrote:
> On Thu, Jul 2, 2015 at 11:35 AM, Anne van Kesteren <annevk@annevk.nl> wrote:
>> Say I host evil.example. I allow images to be loaded from
>> target.example exclusively through CSP. target.example uses
>> credentials to redirect loads to username.target.example. Would
>> evil.example not receive CSP reports with usernames extracted from
>> target.example?
> 1. The changes in CSP2 prevent path leakage, but we don't have a mechanism
> for preventing hostname leakage. The `CSP` header can allow the server to
> mitigate the risk by deciding not to redirect in certain cases, but there's
> no client side mitigation in place.

It seems pretty bad that CSP reports introduced this kind of leak. Why
would we reveal the target of the redirect?

> 2. `unsafe-redirect` does not prevent this attack, as `evil.example` is in
> control of the policy which governs redirect behavior. That is,
> `evil.example`'s CSP will contain `unsafe-redirect`, the redirect will fire,
> and `evil.example` will get a violation report.

Sure, I was not really talking about unsafe-redirect anymore. More
about CSP violating the security principles around redirects.

Received on Thursday, 2 July 2015 10:03:57 UTC

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