> On 6 mar 2015, at 07:14, John C Klensin <john-ietf@xxxxxxx> wrote: > >> One description of >> a threat model to DNS, including description of what >> threats DNSSEC is intended to defend against can be found >> in RFC 3833 [RFC3833]. >> >> If for example the URI resource record is not signed with >> the help of DNSSEC and validated successfully, trusting the >> non-signed URI might lead to a downgrade attack. > > While this may be obvious to experts, the experts probably don't > need it. For everyone else, you are probably missing a > statement about interception, changes to the query or URI, and a > system that won't respond as intended to STARTTLS or equivalent. > Note, in particular, that if one started out with: > > > foo.example.com. IN URI 0 0 good.example.com. > > and a query for that produced a response that contained > foo.example.com. IN URI 0 0 evil.example.com. > > That would clearly be a problem for DNSSEC but, if both of the > hosts designated by "good" and "evil" responded to STAETTLS by > opening TLS connections at desired degrees of security, there > would be no downgrade attack, "only" a MITM host diversion > attack. Well, I to some case disagree and I also thought that that was what Sam pointed out...one wanted to communicate with something at foo.example.com, and if one "normally" did use HTTP over TLS and got a 301 or 302 back, and now instead do a similar change of target with the help of DNS, you do get something very similar at least to a downgrade attack. But I understand what your point is -- I claim ;-) Patrik
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