Re: [Full-Disclosure] mysql password cracking
From: Chris Anley (chris_at_ngssoftware.com)
To: email@example.com Date: Mon, 11 Oct 2004 09:15:01 +0100
Re: allowing users to see other user's hashes - it's dangerous; don't do
it if you don't have to.
To precis what's in the paper (which I wrote btw), there's a few
interesting points about mysql password hashes:
1) In versions prior to 4.1, the password hash can be used to
authenticate directly with the database, so you don't need to crack it.
In other words, knowledge of the *hash* is what the authentication
protocol tests, not knowledge of the password. Admittedly you'd need to
modify your mysql client to authenticate this way but that's not too hard.
2) In versions 4.1 or better (which are still Beta) MySQL uses SHA1 to
hash the passwords, so the situation is a little better. You can still
crack sha1 password hashes fairly easily though, depending on the
password complexity and length. The hashing algorithm is to sha1 hash
the password, then sha1 hash the resulting hash, in other words
sha1(sha1(password)). Of course, if you're using 4.1 or better you're
using beta software, against MySQL AB's recommendation.
3) If you use 4.1 ensure it's at least 4.1.3, because of the
authentication bug detailed in the paper which (briefly) lets any user
authenticate without needing to know the password.
If for some reason you have to have an untrusted user viewing another
user's grants, you could do it safely a number of ways (assuming version
a) Write a UDF to do it (probably the best solution)
b) Write a batch script that periodically does the 'show grants', strips
the password hashes out and then inserts the data into a table your user
can see. Of course, the data won't be current, but that might be ok and
you don't need to mess about with dangerous privs.
c) Grant the user select privilege (only) on mysql.db, mysql.host,
tables_priv, user_priv and every column of 'mysql.user' apart from
'password', and 'select' their privs out manually. This may be
dangerous, so be careful.
Hope that helps... :o)
Willem Koenings wrote:
>>I'm wondering how dangerous it is to allow a user on a
>>mysql db to view the grants for another user. Could
>>they take the encrypted password data and possibly
>>crack it? If they can, how easy is it?
> on certain condition it's quite easy, if you have
> a hash:
> test.exe 57510426775c5b0f
> Hash: 57510426775c5b0f
> Trying length 3
> Trying length 4
> Trying length 5
> Found pass: guest
> some reading for you:
> all the best,
Full-Disclosure - We believe in it.