Excerpt from:
http://www.xmpp.org/internet-drafts/draft-saintandre-rfc3920bis-06.html
"Section: 8.3. Generation of Resource Identifiers
A resource identifier can be security-critical. For example, if a malicious
entity can guess a client's resource identifier then it may be able to
determine if the client (and therefore the controlling principal) is online or
offline, thus resulting in a presence leak as described under Section 15.13
(Presence Leaks). Traditionally, XMPP resource identifiers have been generated
by clients in ways that are not secure (e.g., hardcoding the resource
identifier to the name of the client or to a common location such as "home" or
"work"). However, for the sake of proper security, a resource identifier SHOULD
be random (see [RANDOM] (Eastlake, D., Schiller, J., and S. Crocker,
“Randomness Requirements for Security,” June 2005.)). It is RECOMMENDED that
the resource identifier incorporate a Universally Unique Identifier (UUID), for
which the format specified in [UUID] (Leach, P., Mealling, M., and R. Salz, “A
Universally Unique IDentifier (UUID) URN Namespace,” July 2005.) is
RECOMMENDED. "
From the IMPP RFC I get that:
X can read Y's presence info only
(A) if Y's presence info is public domain, or
(B) if Y previously allowed X to read it's presence.
In this case, when a malicious entity, that can guess X's resource identifier,
is be able to read X's presence only if (A) or (B) is true, in which case it is
not a security threat, it is by default. What I am saying is that the presence
leaks are not related with the easiness of guessing X's resource IDs but if the
server is handling correctly the presence information for a given JID.
Also, the requirement to have a resource identifier be random "for the sake of
proper security" it is also a forced and unnecessary requirement. The server
should guarantee the security by implementing correctly a secure protocol not
by following recommendations.
It is very possible to have missed some angles here, I am pretty new in this
world, please correct me if I am wrong.
Ovidiu
