Subject: [DNSOP] Review of draft-ietf-dnssd-mdns-dns-interop-01

From: "Hosnieh Rafiee" <[email-masked]>
Date: Wed, 22 Jul 2015 07:43:21 +0200

Hello,

I reviewed this draft. to be clear, I am not expert in unicode or
internationalized charactersets. My comments are as followings:

I think there is attack on the interopration of mDNS and unicast DNS and I
think applicable to this draft while in the security consideration, it is
not mentioned any mitigation mechanism.

- mixing mDNS and unicast DNS names
poor implementation might allow an attacker to response to unicast DNS query
request sent by a client for the purpose of resolving a global domain name.

If the mDNS requests are prioterize, there is a possibility that the client
accepts the mDNS response and prioterize it over unicast DNS names.
Therefore, the attacker has a chance to offer a fake response . The risk of
this attack is higher when the internationalized character set is allowed in
unicast DNS server. 

The possible mitigation is authentication of a service as well as the
unicast DNS

Now the question is that is it possible also to cheat the recursive resolver
with mDNS responses while looking up for a domain?

If the priority for looking up names is first unicast DNS and then mDNS,
then in this case there might be a lot of traffic to unicast DNS servers and
if it is the other round, then there might be the possibility of the attack
mentioned above

mitigation: authentication of recursive resolver

- section 3
<snip> U-labels cannot contain upper case letters </snip>

For some languages, upper case letter does not make it different specially
in some letters. Especially the languages that a word is the result of
attaching the characters together.  I think this is specially true for
non-european languages. Two examples are  Persian or Arabic.

Therefore, one cannot differentiate between mDNS service and DNS names with
only considering that DNS cannot use uppercase U-labels.

- section 4.2
It is not the requirement of DNSSD to use underscoll character, as far as I
can see it is only recommendation. please see
https://tools.ietf.org/html/rfc6763#section-7
Therefore, the attacker can use the similar domain names as unicast DNS for
its fake service which might result in confusion of the recursive DNS
servers 

Thanks,
Best,
Hosnieh

> -----Original Message-----
> From: dnssd [mailto:[email-masked]] On Behalf Of Ralph Droms
> (rdroms)
> Sent: Tuesday, July 21, 2015 10:06 AM
> To: [email-masked]
> Subject: [dnssd] Requesting review of draft-ietf-dnssd-mdns-dns-interop-01
> 
> Hi - The dnssd chairs would like to get some reviews of
draft-ietf-dnssd-mdns-
> dns-interop-01, "On Interoperation of Labels Between mDNS and DNS," from
> dnsop participants.  draft-ietf-dnssd-mdns-dns-interop-01 is currently in
dnssd
> WG last call and last call comments will be discussed in the dnssd WG
meeting
> this week.
> 
> Please post your feedback to dnsop or send to Tim and myself.
> 
> - Ralph
> 
> Bcc: [email-masked]
>