Horton

Re: SCRAM with channel binding downgrade attack

Bruce Momjian <bruce@momjian.us>

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From: Bruce Momjian <bruce@momjian.us>
To: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
Cc: Heikki Linnakangas <hlinnaka@iki.fi>, Michael Paquier <michael@paquier.xyz>, Magnus Hagander <magnus@hagander.net>, PostgreSQL-development <pgsql-hackers@postgresql.org>, Stephen Frost <sfrost@snowman.net>
Date: 2018-10-05T17:01:41Z
Lists: pgsql-hackers 
On Fri, Oct  5, 2018 at 04:53:34PM +0200, Peter Eisentraut wrote:
> On 23/05/2018 08:46, Heikki Linnakangas wrote:
> > "tls-unique" and "tls-server-end-point" are overly technical to users. 
> > They don't care which one is used, there's no difference in security. 
> 
> A question was raised about this in a recent user group meeting.
> 
> When someone steals the server certificate from the real database server
> and sets up a MITM with that certificate, this would pass
> tls-server-end-point channel binding, because both the MITM and the real
> server have the same certificate.  But with tls-unique they would have
> different channel binding data, so the channel binding would detect this.
> 
> Is that not correct?

Not correct.  First, they need to steal the server certificate and
_private_ key that goes with the certificate to impersonate the owner of
the certificate.  If that happens, with tls-server-end-point, a MITM
could replay what the real server sends to the MITM.  You are right that
tls-unique makes it harder for a MITM to reproduce the TLS shared key
which is mixed with the password hash to prove the server knows the
password hash.

I think the standard is now focusing on tls-server-end-point because
most APIs make the certificate more accessible than the TLS shared key. 
There also might be exploits with TLS shared keys being cached to
improve SSL performance, particularly for https access:

	https://tools.ietf.org/html/draft-badra-tls-key-exchange-00

Of course, that is just a guess.

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

+ As you are, so once was I.  As I am, so you will be. +
+                      Ancient Roman grave inscription +

Commits

  1. doc: update PG 11 release notes

  2. Fix misspelled pg_trgm contrib name in PostgreSQL 11 release notes

  3. Doc: clarify release note text about v11's new window function features.

  4. Improve wording of release notes item

  5. Fix typos in release notes

  6. Doc: preliminary list of PG11 major features.

  7. Make numeric power() handle NaNs according to the modern POSIX spec.

  8. Various improvements of skipping index scan during vacuum technics

  9. Revert back-branch changes in power()'s behavior for NaN inputs.

  10. Avoid wrong results for power() with NaN input on more platforms.

  11. Avoid wrong results for power() with NaN input on some platforms.

  12. Skip full index scan during cleanup of B-tree indexes when possible

  13. Rewrite the code that applies scan/join targets to paths.

  14. Postpone generate_gather_paths for topmost scan/join rel.

  15. Add casts from jsonb

  16. Make plpgsql use its DTYPE_REC code paths for composite-type variables.

  17. Don't allow VACUUM VERBOSE ANALYZE VERBOSE.

  18. Pass InitPlan values to workers via Gather (Merge).

  19. Account for the effect of lossy pages when costing bitmap scans.

  20. Allow no-op GiST support functions to be omitted.

  21. Rearm statement_timeout after each executed query.

  22. Push limit through subqueries to underlying sort, where possible.