Re: [sip-overload] AD review of draft-ietf-soc-load-control-event-package-08

[Richard Barnes <[e-mail]>]

Dear authors,

Thanks for updating this document.  It looks much better.  Sorry for the
delay in my reply.

The one thing I don't think is quite adequately addressed by the
considerations around the use of the "redirect" action.

The attack I'm worried about is something like the following:
-- A bunch of proxies in a Trust Domain are using UDP, and configured to
get their policies from a central server.
-- Attacker spoofs the server's address to send a bunch of NOTIFY bodies
telling proxies to send all calls to [e-mail]
-- Proxies redirect all calls to victim, who is now DoSed off of the
Internet

In order to address this threat, you need to either (1) remove the
"redirect" action, or (2) constrain redirects to a safe space.  I assume
that the WG doesn't want to do (1) :)

Proposed edits:
-- Add to the definition of a Trust Domain an agreement on the types of
calls that can be affected by load control.  For example, <one> and <many>
element might be limited to specific domains; <*-tel> elements might be
limited to be within certain prefixes.
-- Add to the definition of a Trust Domain an agreement on the destinations
to which calls may be redirected.  For example, the URI might have to match
a given set of domains.
-- Add text to the Security Considerations describing the above attack, and
REQUIREing that implementations enforce the limits described in the
definition of their Trust Domain.

Thanks,
--Richard






On Wed, Apr 17, 2013 at 1:53 PM, Richard Barnes <[e-mail]> wrote:

> I have reviewed this document, and have a few questions before IETF LC:
>
> Major:
>
> In a few places, for example Section 5.3., the document suggests that this
> event package could be used to communicate load filtering policies between
> domains.  This seems like a bad idea for a few reasons.  First, policies
> can be based on "P-Asserted-Identity", which is itself limited to use
> within a trust domain / Spec(T).  It doesn't make sense to have policies
> based on these identifiers outside of the domain in which they are used.
>  Second, inter-domain policies can create subtle and dangerous security
> risks.  For example, according to the current specification, Domain A could
> tell Domain B to drop all calls between Domain B and Domain C.  It's not
> clear how you would prevent these sorts of attacks, especially where "tel:"
> URIs are involved.  I think both of these issues go away if this event
> package is limited in a similar way to P-Asserted-Identity, i.e., limited
> to use within a trust domain.
>
> Section 6.3., "SUBSCRIBE Bodies" doesn't actually say anything about what
> goes in the body of a SUBSCRIBE message.  On the one hand, it implies that
> there could be a body (since the last sentence considers a request without
> a body as a special case), but it doesn't say what goes in the body if
> there is one.  Please either (1) define what may go in the body, (2)
> explicitly say that this document does not specify what goes in SUBSCRIBE
> bodies, or (3) require that the body be empty.   (Also, the first paragraph
> of this section seems out of place here, since it also has nothing to do
> with the body.)
>
> In Section 6.5., the last sentence is wrong.  The presence of an Accept
> header indicates that the response body should be one of the indicated
> types.  The indicated behavior would only be acceptable if the Accept
> header included "multipart/mixed".  Suggest deleting the last sentence.
>  (Also,  it would be clearer to change "the request body will contain" to
> "the request body MUST contain".)
>
> In Section 7.3.1, you need to specify how a "tel:" URI is matched against
> a domain value starting with "+".  Your examples seem to indicate simple
> string prefix matching, but I doubt that's what you actually want, since
> non-digit characters can break things.  For example, "+1212" should match "
> [phone]".  Please specify a matching algorithm here.
>
> In Section 7.3.2, please change "Non-initial requests ... are not
> subjected" to "Non-initial requests ... MUST NOT be subjected".
>
> Section 7.4. doesn't adequately define the actions to be taken.  Each of
> the action elements (<rate>, <window>, <percent>) need to define a concrete
> action that the proxy should take.
>
> RFC 4745 allows rules to combine when multiple rules match a given call.
>  This document needs to define combination rules for the actions defined
> here.
>
> What's the reason for having both the "drop" action and the "reject"
> action?  It seems like the "drop" action is almost always harmful.  With
> unreliable transport, it causes retransmits, and even with reliable
> transport, it causes the client to wait unnecessarily until the connection
> times out.  In any case, the "simple drop" action is underspecified.  For
> example, does the server simply ignore the SIP message, or does it close
> the transport connection?
>
>
> Minor:
>
> In Section 7.3, "we re-define" -- the document doesn't re-define any of
> the elements in RFC 4745 (that's good; redefinition is bad).  Instead, you
> should say you define new identity elements.
>
> In Section 7.3.1, please break up paragraph starting "To include the two
> forms..." for greater readability.  Suggested break points: Before "Note
> that the tradeoff...", and before "It should be noted..."
>
> In Section 7.3.3, it would be helpful to break up the paragraph starting
> "The following are two example...".  Break before "Usecase I" and "Usecase
> II".  Also, s/Usecase/Use case/g
>
>
> Thanks,
> --Richard
>