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From Ian Clelland <iclell...@chromium.org>
Subject Re: How to handle CSP for XHR in Cordova 4.0
Date Wed, 17 Dec 2014 21:01:37 GMT
I think that access tags (and the widget spec generally) were never a good
fit for the top-level-navigation case. Widgets, as far as I know, were
always intended to be single page apps, and the <access> tag wouldn't have
any affect on that at all.

We've used it for nav in the past, though, so the question is whether
familiarity with the old syntax trumps the fact that we're changing the
behaviour.

On Wed Dec 17 2014 at 11:47:02 AM Chuck Lantz <clantz@microsoft.com> wrote:

> I suppose that is a good question. I took a look at the Widget Access
> Request Policy W3C spec where that element comes from.  It's actually
> pretty ambiguous.
>
> "A user agent enforces an access request policy. ... In the default
> policy, a user agent must deny access to network resources external to the
> widget by default, whether this access is requested through APIs (e.g.
> XMLHttpRequest) or through markup (e.g. iframe, script, img).."
>
> ... but...
>
> "A user agent may apply a different default policy if the widget is being
> used in a context that defines its own policy, such as for instance a
> widget served over HTTP. A more lenient policy can be defined with the
> access-request list as defined in the processing section. ... Furthermore,
> a user agent may grant access to certain URI schemes (e.g., mailto:)
> without the need of an access request if its security policy considers
> those schemes benign."
>
> It strikes me that today we implement the default policy and what we're
> proposing here is a more lenient, alternate policy.
>
> For what it's worth, here's how this is defined in the Windows world:
>
>       <ApplicationContentUriRules>
>           <Rule Match="https://www.google.com" Type="include" />
>       </ApplicationContentUriRules>
>
> -Chuck
>
> -----Original Message-----
> From: Ian Clelland [mailto:iclelland@chromium.org]
> Sent: Wednesday, December 17, 2014 8:16 AM
> To: dev@cordova.apache.org
> Subject: Re: How to handle CSP for XHR in Cordova 4.0
>
> Definitely want to handle iOS, with the same policy. I've been working on
> that in parallel with Android.
>
> Do we want to use <access> for Nav? I wasn't sure, given its history, and
> the fact that we're changing its behaviour. Is it better to stick with the
> familiar tag and change what it tries to do? Or create a new tag and
> deprecate <access>?
>
> On Wed Dec 17 2014 at 10:30:18 AM Chuck Lantz <clantz@microsoft.com>
> wrote:
>
> > What about top level nav and script access?  Would the thought be that
> > the <access> elements would map to that in the base platform?  I'm
> > thinking in terms of consistency across the different platforms.  It
> > strikes me we'd want to update iOS at least as well.
> >
> > -Chuck
> >
> > -----Original Message-----
> > From: agrieve@google.com [mailto:agrieve@google.com] On Behalf Of
> > Andrew Grieve
> > Sent: Tuesday, December 16, 2014 7:21 AM
> > To: dev
> > Subject: Re: How to handle CSP for XHR in Cordova 4.0
> >
> > On Mon, Dec 15, 2014 at 8:19 PM, Chuck Lantz <clantz@microsoft.com>
> wrote:
> > >
> > > Near term, for Windows 8.0/8.1, a custom security policy is in place
> > > at the platform level for store apps so CSP doesn't really apply
> > > there at the moment. (And, to be really specific, CSP support is
> > > pretty limited in
> > > IE10/11 focusing on the sandbox directive. The Windows 10 Tech
> > > Preview is where you can see the real support in IE right now.) So,
> > > it's a more of forward-thinking topic in that world.
> > >
> > > A related question, however - CSP support only started in the
> > > Android browser with 4.4 did it not? Obviously Crosswalk would have
> > > it but what about when using the base browser?  Is the thought devs
> > > should use the old whitelist model here?
> > >
> >
> > I think one of the big issues is that the whitelist never worked for
> > blocking *all* requests. It didn't work pre-3.0, and it doesn't block
> > <audio>, <video>, websocket in any version. Supporting the illusion
of
> > a whitelist is probably worse than not supporting it at all.
> >
> >
> >
> > >
> > > Safari seems to support it back at least as far as iOS 7 (or 6 with
> > > a custom header) - the main reason I bring it up is developers could
> > > see different behaviors between devices and versions if the default
> > > CSP policy leaves something like inline or eval disabled.
> > >
> > > -Chuck
> > >
> > > -----Original Message-----
> > > From: Ian Clelland [mailto:iclelland@chromium.org]
> > > Sent: Monday, December 15, 2014 11:17 AM
> > > To: dev@cordova.apache.org
> > > Subject: Re: How to handle CSP for XHR in Cordova 4.0
> > >
> > > On Mon Dec 15 2014 at 11:28:43 AM Chuck Lantz <clantz@microsoft.com>
> > > wrote:
> > >
> > > > For the Windows platform, IE 10 and 11 support CSP 1.0 - there's
> > > > one subtle difference (X-Content-Security-Policy vs
> > > > Content-Security-Policy in the HTTP header).  The Win 10 Tech
> > > > Preview
> > > already has full CSP support.
> > > > In general, the conventional wisdom is to push app models towards
> > > > the CSP and away from custom enforcement policies from our point
> > > > of
> > view.
> > > > I love the idea of Cordova heading this same direction.
> > > >
> > >
> > > That's great to hear.
> > >
> > > >
> > > > Windows apps have a URI whitelist focused on top level navigation
> > > > and JavaScript includes on pages not XHR. The main reason to lock
> > > > down at this level is to reduce the risk of a malicious user
> > > > navigating the page to a URI outside of the app author's control
> > > > and take advantage of sensitive APIs.  So, I think some level of
> > > > whitelist to help out in this situation is advisable even with CSP
> > > > being used. We’ve mapped <access> elements in config.xml to the
> > > > top level nav whitelist for this reason. CSP isn’t really designed
> > > > to help
> > with this kind of problem.
> > > >
> > >
> > > Agreed. CSP on the web can't really control navigation, or else web
> > > page authors would be able to trap browser windows on their sites.
> > > It makes sense for installed apps, but not so much for sites or web
> apps.
> > >
> > >
> > > >
> > > > Perhaps a default CSP policy in the template coupled with a top
> > > > level nav whitelist is the right starting point.
> > >
> > >
> > > That sounds like what I'm trying to implement on Android and iOS.
> > > Let me know what I can do to make that easy for Windows.
> > >
> > >
> > > > Determining what the CSP policy looks like will be really
> > > > important – by default CSP blocks both inline and eval use. Of the
> > > > two, inline use tends to be the bigger risk factor.
> > > >
> > >
> > > True -- eval without inline can theoretically be controlled,
> > > although it's not great practice. inline, with or without eval is an
> > > XSS waiting to happen, in a web app.
> > >
> > >
> > > >
> > > > -Chuck
> > > >
> > > > -----Original Message-----
> > > > From: Ian Clelland [mailto:iclelland@google.com]
> > > > Sent: Friday, December 12, 2014 9:34 AM
> > > > To: dev@cordova.apache.org
> > > > Subject: Re: How to handle CSP for XHR in Cordova 4.0
> > > >
> > > > Default CSP is a good idea. I was worried about leaving new apps
> > > > vulnerable by default but that should close that.
> > > >
> > > > Do we know what the CSP story is on all platforms, to know that it
> > > > won't break anything else?
> > > > On 12 Dec 2014 11:56, "Michal Mocny" <mmocny@chromium.org> wrote:
> > > >
> > > > > I'm fine with 1. coupled with a default CSP in the template
> > > application.
> > > > >
> > > > > For older apps not written from scratch, we can perhaps strongly
> > > > > suggest installing the legacy-whitelist, which would change the
> > > > > default-open behaviour to default-closed.
> > > > >
> > > > > Together, that would give sensible defaults that aren't
> > > > open-to-everything?
> > > > >
> > > > > -Michal
> > > > >
> > > > > On Fri, Dec 12, 2014 at 9:13 AM, Ian Clelland
> > > > > <iclelland@chromium.org>
> > > > > wrote:
> > > > >
> > > > > > I'm just building the new optional whitelist plugins for
> > > > > > Cordova Android and iOS 4.x, and I'm thinking about how to
> > > > > > encourage developers to use
> > > > > CSP
> > > > > > for network requests, as opposed to a
> > > > > > Cordova-implemented-whitelist-which-probably-leaks-like-a-sieve.
> > > > > >
> > > > > > (Note: This is really just about things like XHR requests,
> > > > > > <img> and <script> tags, etc, which are historically
the only
> > > > > > things that we've reliably been able to filter out. Other
> > > > > > classes of network requests just bypass all of our code
> > > > > > anyway, which sucks, and frame navigation and external
> > > > > > application launches are already well handled
> > > > by the framework).
> > > > > >
> > > > > > The policy I've implemented on the unplug-whitelist branches,
> > > > > > which at first thought at least *sounds* sane, is that network
> > > > > > requests are
> > > > > blocked
> > > > > > by default. (At least all of the ones that we can intercept).
> > > > > > That way, a plugin, such as the legacy-whitelist plugin, can
> > > > > > open up access to
> > > > > specific
> > > > > > resources, and the fallback is safety.
> > > > > >
> > > > > > To use CSP, though, we have to open up access to the outside,
> > > > > > and we
> > > > > don't
> > > > > > necessarily know what the developer wants to open (the whole
> > > > > > point is
> > > > > that
> > > > > > they specify in the HTML, not in a config file.) The easiest
> > > > > > way is to
> > > > > open
> > > > > > up access to *all* resources to the webview, and then restrict
> > > > > > it through the CSP header/meta-tag, which does a better job
of
> > > > > > blocking those
> > > > > requests
> > > > > > than we do in any case.
> > > > > >
> > > > > > I think that we want to encourage developers to use CSP, for
a
> > > > > > lot of reasons, but I'm going to have to do one of these
> > > > > > things, and I'm not entirely sure which is the right one:
> > > > > >
> > > > > > 1. Open access to all network resources by default in Cordova
> 4.x.
> > > > > >   * This doesn't apply to navigations, or launching other apps.
> > > > > > They're still blocked by default.
> > > > > >   * Any plugin implementing shouldAllowRequest would still be
> > > > > > able to
> > > > > turn
> > > > > > this into a disallow-by-default whitelist
> > > > > >   * We can't block everything anyway (see websockets,
> > > > > > audio/video
> > > > > streams /
> > > > > > probably more), so it removes the illusion that we can.
> > > > > >
> > > > > > 2. Make another whitelist-y plugin, something like
> > > > > "org.apache.cordova.csp"
> > > > > > that exists only to open up access to network resources.
> > > > > > Direct all users who want to use CSP to install that plugin
first
> > > > > >   * It's a 4th network plugin (after legacy-whitelist,
> > > > > navigation-whitelist
> > > > > > and intent-whitelist)
> > > > > >   * Adding it doesn't actually add any CSP protection, so it
> > > > > > probably
> > > > > needs
> > > > > > a better name
> > > > > >   * It's an extra step that may confuse people and limit
> > > > > > adoption
> > > > > >
> > > > > > 3. Do something crazy. Maybe a CSP plugin that automatically
> > > > > > creates CSP tags *and* updates the XHR whitelist, both from
> > > > > > config
> > > directives.
> > > > > >   * Lots more work
> > > > > >   * We probably don't know enough about real requirements to
> > > > > > get this
> > > > > right
> > > > > >   * If CSP is doing its job, then the XHR whitelist isn't
> > > > > > needed anyway;
> > > > > it
> > > > > > would just be another layer that isn't doing anything different.
> > > > > >
> > > > > > I'm leaning towards #1, but its a it's a decision that we
> > > > > > really should think about and decide on-list before moving
> forward.
> > > > > >
> > > > > > Ian
> > > > > >
> > > > >
> > > >
> > > > ------------------------------------------------------------------
> > > > --
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> > > > For additional commands, e-mail: dev-help@cordova.apache.org
> > > >
> > >
> >
>
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