[Standards] Addressing Security Concerns in XEP-0115 Entity Capabilities

Dave Cridland dave at cridland.net
Mon Sep 5 12:39:08 UTC 2011


On Wed Aug 31 06:48:26 2011, Waqas Hussain wrote:
> Most protocol attacks are based on unexpected input. Attackers
> wouldn't really care whether the values they send are registered or
> usable in any way, as long as the attack succeeds. I don't think you
> are proposing all caps handling entities ship with a copy of the
> registry and fail on anything not included.

No, but we could potentially restrict input quite heavily.

Let's say that we add (yet) another attribute to the caps element,  
indicating that the "new" restrictions are in place. (These might  
include the various restrictions mentioned in this thread).

Now, when a client sees a caps marked as restricted, it can validate  
the disco#info it gets.

If a client sees two caps strings, one marked as restricted and one  
not, it should assume that the caps string is intended to be  
restricted as proceed accordingly.

I'm also wondering if it's worth considering optional (and marked)  
removal of XEP-0128 in cases where it's not used.

Of course, it may be simplest just to bite the bullet and switch hash  
algorithm - or even change the 'hash' attribute name - because then  
it'll get treated as a pre-1.4 caps by the vast majority of entities  
and everything will happen right (or at least, no worse than it often  
does today anyway).

I'm gradually leaning toward this, because although it's *quite*  
violent, the downside is not impossible.

BTW, anyone any idea what happens if you include more than one <c/>  
in a presence, in practical terms?

> I know Miranda and Tkabber send software version. Probably many
> others. Can we gather stats on jabber.org for this?

M-Link cannot capture that data, except by capturing all traffic  
(which is inadvisable).

I would re-iterate that we still have no burning building. We're  
getting closer, though.

Dave.
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