Horton

Re: SCRAM with channel binding downgrade attack

Magnus Hagander <magnus@hagander.net>

View thread View on postgr.es
From: Magnus Hagander <magnus@hagander.net>
To: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>, Bruce Momjian <bruce@momjian.us>, Michael Paquier <michael@paquier.xyz>, Robert Haas <robertmhaas@gmail.com>, Heikki Linnakangas <hlinnaka@iki.fi>, Postgres hackers <pgsql-hackers@postgresql.org>, Stephen Frost <sfrost@snowman.net>
Date: 2018-06-28T08:07:44Z
Lists: pgsql-hackers 
On Thu, Jun 28, 2018 at 10:04 AM, Peter Eisentraut <
peter.eisentraut@2ndquadrant.com> wrote:

> On 6/28/18 09:35, Magnus Hagander wrote:
> > No, we absolutely still have SCRAM channel binding.
> >
> > *libpq* has no way to *enforce* it, meaning it always acts like our
> > default SSL config which is "use it if available but if it's not then
> > silently accept the downgrade". From a security perspective, it's just
> > as bad as our default ssl config, but unlike ssl you can't configure a
> > requirement in 11.
>
> Isn't this similar to what happened whenever we added a new or better
> password method?  A MITM that didn't want to bother cracking MD5 could
> just alter the stream and request "password" authentication.  Same with
> MD5->SCRAM, SCRAM->SCRAM+CB, and even a hypothetical future change in
> the SCRAM hashing method.  Clearly, we need a more comprehensive
> solution for this.
>

That is sort of the gist of the discussion, yes. It is.

So if you just enabled scram channel binding, an attacker could just turn
off scram completely.

That's why we need a solution that covers the full problem, which is why it
needs to be thought of as one problem so we don't end up with a fragmented
solution.

-- 
 Magnus Hagander
 Me: https://www.hagander.net/ <http://www.hagander.net/>
 Work: https://www.redpill-linpro.com/ <http://www.redpill-linpro.com/>

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.