Bugtraq mailing list archives
Re: [HACKERS] Postgres: pg_hba.conf, md5, pg_shadow, encrypted passwords
From: Tom Lane <tgl () sss pgh pa us>
Date: Wed, 20 Apr 2005 17:03:18 -0400
Stephen Frost <sfrost () snowman net> writes:
The md5 hash which is generated for and stored in pg_shadow does not use a random salt but instead uses the username which can generally be determined ahead of time (especially for the 'postgres' superuser account).
So? The fact that we encrypt the contents of pg_shadow at all is not to provide security against breakins by people who have managed to obtain the contents of pg_shadow. Any such attacker knows as much as the postmaster does, and so there isn't anything much the postmaster can do to prevent a breakin. The reason we do it is to prevent such a person (or a dishonest DBA) from obtaining the user's actual original password. This doesn't improve the security of the database at all, of course, but it does improve security globally if the user used the same password for other systems.
This would allow for the pregeneration of the entire md5 keyspace using that 'salt' and then quick breakage of the hash once it's retrieved by the attacker.
Considering the size of the possible keyspace, this is pretty silly.
Were a decent random salt of some size used it would be difficult to guess and pregenerate the keyspace for. Thus, keyspace generation would have to happen after pg_shadow was compramised, giving the admin time to detect the compramise and take corrective action.
Another large assumption: that the admin knows about the compromise before the results are used.
. It is also not made clear that if you are already handling transport-level security via SSL and/or IPSEC that using md5 actually reduces security by not adding anything to the transport-level security and defeating the on-disk security effectivness of using md5 for pg_shadow.
That's simply false. The contents of pg_shadow are never sent over the wire. You're going to have to work a lot harder to convince us there's any significant issue here. regards, tom lane
Current thread:
- Postgres: pg_hba.conf, md5, pg_shadow, encrypted passwords Stephen Frost (Apr 20)
- Re: Postgres: pg_hba.conf, md5, pg_shadow, encrypted passwords David F. Skoll (Apr 20)
- Re: Postgres: pg_hba.conf, md5, pg_shadow, encrypted passwords Stephen Frost (Apr 20)
- Re: [HACKERS] Postgres: pg_hba.conf, md5, pg_shadow, encrypted passwords Tom Lane (Apr 20)
- Re: [HACKERS] Postgres: pg_hba.conf, md5, pg_shadow, encrypted passwords Jim C. Nasby (Apr 20)
- Re: [HACKERS] Postgres: pg_hba.conf, md5, pg_shadow, encrypted passwords Tom Lane (Apr 20)
- Re: [HACKERS] Postgres: pg_hba.conf, md5, pg_shadow, encrypted passwords Bruce Momjian (Apr 20)
- Re: [HACKERS] Postgres: pg_hba.conf, md5, pg_shadow, encrypted passwords Tom Lane (Apr 20)
- Re: [HACKERS] Postgres: pg_hba.conf, md5, pg_shadow, encrypted passwords David F. Skoll (Apr 21)
- Re: [HACKERS] Postgres: pg_hba.conf, md5, pg_shadow, encrypted passwords Jim C. Nasby (Apr 20)
- Re: [HACKERS] Postgres: pg_hba.conf, md5, pg_shadow, encrypted passwords Jim C. Nasby (Apr 20)
- Re: [HACKERS] Postgres: pg_hba.conf, md5, pg_shadow, encrypted passwords Stephen Frost (Apr 21)
- Re: [HACKERS] Postgres: pg_hba.conf, md5, pg_shadow, encrypted passwords Bruno Wolff III (Apr 22)
- Re: [HACKERS] Postgres: pg_hba.conf, md5, pg_shadow, encrypted passwords Stephen Frost (Apr 22)
- Re: [HACKERS] Postgres: pg_hba.conf, md5, pg_shadow, encrypted passwords Antoine Martin (Apr 22)
- Re: Postgres: pg_hba.conf, md5, pg_shadow, encrypted passwords David F. Skoll (Apr 20)