Re: <?access-control?> allows privelege escalation attacks with many embedding mechanisms

On Thu, 16 Feb 2006, Maciej Stachowiak wrote:
> 
> - Any loading or embedding mechanism that gives access to the resulting 
> http headers would prevent the use of <?access-control?> for any XML 
> document on a server that uses cookies for login. A resource from 
> another source would be able to steal the cookie,

Indeed; any resource that returns an <?access-control?> PI would have to 
be one that the server knows will not be associated with any 
DOM-accessible authentication information.

(Note that this isn't privilege escalation, it's authentication leakage 
or cookie theft.)


> - Any loading or embedding mechanism that gives read/write access to the 
> target's DOM cannot be used safely with <?access-control?>, because the 
> loaded document can be used to execute script and reflect requests for 
> resources that are supposed to be inaccessible.

For the use case that first started us looking at <?access-control?>, this 
type of privilege escalation would not be possible. The use case was 
off-site XBL2. This case would not be susceptible to this attack because 
third-party XBL2, like third-party CSS, runs in the security context of 
the source document, not the security context of the XBL2 document.


I agree that <?access-control?> would not be a solution for cross-site 
XMLHttpRequest, <object>, <iframe>, <frame>, or other systems; anyone who 
thinks that it would be is, as you point out, failing to understand the 
scope of the problems.

The use case that originally raised interest in <?access-control?> beyond 
the voice browser working group is, however, safe (assuming the PI is not 
used on sites where cookie theft is an issue). I do not believe anyone has 
seriously suggested that <?access-control?> be used as a generic mechanism 
beyond allowing the use of third-party XBL2.

I agree that the specification should be absolutely clear about these 
risks.

-- 
Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'