Subject: [saag] SECDIR review of draft-hoffman-dns-in-json

From: Watson Ladd <[email-masked]>
Date: Thu, 29 Mar 2018 13:27:42 -0700

Dear all,

I have reviewed this document as part of the security directorate's
ongoing effort to review all IETF documents being processed by the
IESG.  These comments were written primarily for the benefit of the
security area directors.  Document editors and WG chairs should treat
these comments just like any other last call comments.

The summary of the review is ready with issues.

I have some very strong reservations about defining a data format
without some strong round-tripping guarantees and with as much
flexibility as this one. The JSON format for DNS packets is intended
to permit representation of malformed packets, and has a high degree
of flexibility, with an intent that applications define profiles of it
for themselves.

There are considerable security implications to doing this not
addressed in the Security Implications section, in addition to obvious
interoperability issues. For example, if we have a filter for JSON
representations of DNS packets, this filter must share the same
semantics for the output JSON as the consumer, even in the face of
such bizzarities as HEX and regular fields with different contents,
malformed length fields, etc. etc. I expect that this can and will
cause serious issues.

I would suggest we not represent invalid packets and ensure all valid
packets have a unique representation. Failing that the security
consideration should at minimum be amended to include a discussion of
these issues. A schema that can be used to validate DNS packets
represented in JSON could also help address these problems.

Sincerely,
Watson Ladd