390910 - Content Restrictions

Status: RESOLVED DUPLICATE of bug 493857

(Core :: DOM: Core & HTML, defect, P3)

Description

[Robert Sayre]

Allow sites to restrict the types locations of loaded scripts and other unsafe content.

Comment 1

[Robert Sayre]

Attachment: simple test case

when you select-all and view selection source, there should be no onclick attribute and no script element.

Comment 2

[Robert Sayre]

Attachment: HTML patch, no XML/XHTML support

Gerv's initial design implies a blacklist. We should probably flip that to a whitelist. That would make it a lot easier to deal with XML, too.

Comment 3

[Robert Sayre]

Couple of extra changes here:

Changed the header name to "Restriction". Content-* names have special meaning in MIME, so HTML-specific things would be frowned upon.

It also eliminates styles from the body when script=head is specified, because we do all sorts of crazy things in CSS. :(

Still to do:

Change to NOSCRIPT behavior when script=none is specified.
Add plugins=none parameter and disable plugins on the docshell.

Comment 4

[Jonas Sicking (:sicking) No longer reading bugmail consistently]

I'm not very exited about this solution to be honest. Mostly because it contains a blacklist of attribute names which is sure to get out of date.

What I'd rather do is to set a flag on the elements that we want to disable and tell them to not execute any dangerous content. In bug 343037 I have a patch that implements such a flag. (The patch won't land, for other reasons). This would IMHO be a much safer way to block scary content.

Comment 5

[Robert Sayre]

(In reply to comment #4)
> I'm not very exited about this solution to be honest. Mostly because it
> contains a blacklist of attribute names which is sure to get out of date.

Yeah, the patch would need to have that blacklist changed to a whitelist, at the very least.

> What I'd rather do is to set a flag on the elements that we want to disable and
> tell them to not execute any dangerous content. In bug 343037 I have a patch
> that implements such a flag. (The patch won't land, for other reasons). This
> would IMHO be a much safer way to block scary content.

For the record, that patch checks a flag at the point in the code where check "is this a script" and then execute it. It is a good approach, as long as we don't add code that routes around it. Still going to have problems with plugins and styles, though. I don't really have a preference for either approach, so we might as well try both for the moment. Jonas has already written for the alternative approach, so it's not much extra work.

I thought of another concern: serializing dangerous content that is then reloaded without the protection of the Restriction header. A classic Metadata Containment issue[0]. We'll need to elide dangerous content as we serialize.

[0] http://www.goland.org/Tech/spe-whitehead.pdf

Comment 6

[Jonas Sicking (:sicking) No longer reading bugmail consistently]

Plugins should be disabled by the patch, see the change to nsObjectLoadingContent.cpp.

I'm not too worried about the serialize-and-reparse issue. Whatever we do is going to have some limitations so the site will have to know not to be too reckless about the 'foreign' content in its page.

Bindings are unsolved in the patch currently, however that should be pretty easy to fix by adding a check for the flag in the XBL code.

Comment 7

[Robert Sayre]

(In reply to comment #6)
> Plugins should be disabled by the patch, see the change to
> nsObjectLoadingContent.cpp.

Well, one aspect of Gerv's proposal is selective enabling of plugins via the host parameter. We could definitely leave that out as a start, though.
 
> I'm not too worried about the serialize-and-reparse issue. Whatever we do is
> going to have some limitations so the site will have to know not to be too
> reckless about the 'foreign' content in its page.

We wouldn't have this problem if sites weren't reckless. We can definitely play the blame game for many of these exploits, but I think we should make up for the failings of others if it's at all practical.

> 
> Bindings are unsolved in the patch currently, however that should be pretty
> easy to fix by adding a check for the flag in the XBL code.
> 

Nice.

Comment 8

[Jonas Sicking (:sicking) No longer reading bugmail consistently]

Actually, I realized that XBL is taken care of. While you can add bindings to your elements, the contents in those bindings will have the same restrictions as content on your page so it should be harmless.

Comment 9

[Daniel Veditz [:dveditz]]

Brandon has been trying to implement an evolution of this idea as an addon (as a demonstration, without touching the parser he's somewhat limited). Getting this into 3.1 as an experimental feature for websites (using "X-..." headers) would help us move this to a real specification and cross-browser adoption.

I suspect sayrer isn't working on this anymore, and if not this bug could be reassigned to bsterne

Comment 10

[Robert Sayre]

(In reply to comment #9)
> 
> I suspect sayrer isn't working on this anymore, and if not this bug could be
> reassigned to bsterne

Last we talked, I outlined the testcases that such a feature would need to land on the trunk. The bug that blocks this is bug 411791, and that's the one someone should take. No quibbles with the approach.

Comment 11

[Jonas Sicking (:sicking) No longer reading bugmail consistently]

Marking wanted but with relatively low priority for now, until we figure out what way we want to do this.

Comment 12

[Mike Shaver (:shaver emeritus)]

Yeah, should give this to bsterne if he's working it.  The test cases probably need to come first, since getting them in shape will let us reason much more concretely about the threat model, and (as I said in the test case bug) likely enlist some help from the broader security community in making them -- and therefore our solution -- more comprehensive and robust.

Comment 13

[Ray Morris]

Other systems provide the option of a white list 
or black list, such as the LIMIT directive in Apache.
I'd have it default to a white list style approach, 
but for some cases a white list could get very long 
and cumbersome to manage.  In those cases a black 
list would be needed.  It seems at first glance that 
once one is implemented the other would be comparitively 
trivial - simply take the complement, essentially.

Either way, I'd much rather see this implemented in 
some simplistic but extensible way soon than watch it 
sit for the next nine years with no implementation.
Even a simplistic implementation could avoid tens of 
thousands of exploits or more.  Thus I wonder is anyone
still working on this? Brandon?  If not, is there 
interest in a working but very simplistic patch?
I might implement it if it was wanted, but I'm I 
wouldn't implement it all that well.

Comment 14

[Brandon Sterne (:bsterne)]

Thanks for your interest.  Yes, we are still actively pursuing this idea.  One proposal that we are working on is Content Security Policy which you can read more about here:

http://people.mozilla.org/~bsterne/content-security-policy/