From: | Heikki Linnakangas <hlinnaka(at)iki(dot)fi> |
---|---|
To: | Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>, Michael Paquier <michael(at)paquier(dot)xyz> |
Cc: | Postgres hackers <pgsql-hackers(at)postgresql(dot)org>, Robert Haas <robertmhaas(at)gmail(dot)com>, Magnus Hagander <magnus(at)hagander(dot)net>, Stephen Frost <sfrost(at)snowman(dot)net>, Bruce Momjian <bruce(at)momjian(dot)us> |
Subject: | Re: SCRAM with channel binding downgrade attack |
Date: | 2018-06-06 20:53:06 |
Message-ID: | e1f0c36d-62d1-91cd-7b22-0b48e8a6a2f8@iki.fi |
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On 06/06/18 23:31, Peter Eisentraut wrote:
> On 6/6/18 16:26, Heikki Linnakangas wrote:
>> On 06/06/18 23:20, Peter Eisentraut wrote:
>>> Aren't we attacking this on the wrong level? We are here attempting to
>>> prevent a SCRAM-SHA-256-PLUS -> SCRAM-SHA-256 downgrade, but we are not
>>> preventing a SCRAM-SHA-256-PLUS -> anything-else downgrade.
>>
>> The latest patch does prevent that, too. That was my complaint at
>> https://www.postgresql.org/message-id/030284cc-d1d6-ce88-b677-a814f61c1880%40iki.fi,
>> but it's been fixed now. (Or if you see a case where it still isn't,
>> that's a bug.)
>
> OK, that would do, but we don't do anything about a SCRAM-SHA-256 ->
> anything-else downgrade. Instead of tying this to the channel binding,
> should we tie it to the authentication type?
That would certainly be good. We've always had that problem, even with
md5 -> plaintext password downgrade, and it would be nice to fix it.
It's quite late in the release cycle already, do you think we should
address that now? I could go either way..
What should the option look like? Perhaps something like:
allowed_authentication_methods=md5,SCRAM-SHA-256,SCRAM-SHA-256-PLUS
That would not be very user-friendly, though.
- Heikki
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