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Date: Sat, 12 Oct 2013 07:34:20 +0400
From: Solar Designer <solar@...nwall.com>
To: oss-security@...ts.openwall.com
Subject: Re: RESEND: CVE Request: pwgen
Kurt, Steve, all -
On Thu, Oct 10, 2013 at 03:35:09PM +0200, Marcus Meissner wrote:
> It might just not be that CVE worthy. But I saw no replies...
I now think it is CVE worthy.
> (CVE worthyness:
> It does not fully meet the security expectations of generating
> a non-weak password by default....
> )
>
> Solar? Kurt?
Kurt was "sitting on the fence for this one":
http://www.openwall.com/lists/oss-security/2012/01/17/12
At the time, I replied that it was too early for the CVE aspect, as I
was still figuring out the magnitude of the problem:
http://www.openwall.com/lists/oss-security/2012/01/17/14
Steve replied that having an insecure feature documented does not always
preclude from CVE assignment:
http://www.openwall.com/lists/oss-security/2012/01/17/15
To this, I can add that although the phoneme mode is documented as being
less secure, the magnitude and ways in which it is less secure are
unclear from the documentation. Specifically, there's no mention that
the distribution of generated passwords is highly non-uniform, and
indeed this is not clear from merely looking at a handful of passwords.
(I guess this non-uniformity was not expected by the author, and thus it
is a bug.)
Also, without looking at the documentation, it is not even immediately
clear (to a new user of the program) that phonemes are being used.
At first glance, the passwords look like they could potentially use the
full 62^8 keyspace - but this is actually not the case, by far. So the
program's default behavior is misleading.
The thread ended here, with some figures showing just how bad the
problem is:
http://www.openwall.com/lists/oss-security/2012/01/22/6
The CVE aspect was not revisited.
Here are the figures for pwgen's defaults with output to tty:
Top 1 million of unique passwords from my 1 billion training set cracks
3.7% of passwords in the test set.
Top 10 million cracks 14.5%.
Top 44 million cracks 21%. (I chose this as an optimal wordlist size.)
Top 100 million cracks 26.3%.
With pwgen's defaults with output to non-tty:
Top 45.5 million cracks 75%. (Ouch!)
These results can be improved a little bit (slightly higher percentages
cracked per same wordlist size) by using a larger training set (beyond 1
billion) or by considering all of the phoneme probabilities, etc. and
creating a program that would output pwgen's possible passwords in an
optimal order (this proves to be a non-trivial task so far, yet someone
may do it).
Alexander
> On Thu, Sep 26, 2013 at 11:11:59AM +1000, Michael Samuel wrote:
> > Hi,
> >
> > No CVEs have been assigned for this, and as far as I can tell no
> > distributions have patched.
> >
> > On 6 June 2013 14:19, Michael Samuel <mik@...net.net> wrote:
> >
> > > I've done some further analysis of the program after reading the previous
> > > thread, and I think there needs to be CVEs and fixes for:
> > >
> > > - When used from a non-tty passwords are trivially weak by default (first
> > > reported by Solar Designer)
> > > - Phonemes mode has heavy bias and is enabled by default (first reported
> > > by Solar Designer)
> > > - Silent fallback to insecure entropy (first reported by Jean-Michel
> > > Vourg?re) (Debian bug #672241 - tagged as "wishlist")
> > > - Secure mode has bias towards numbers and uppercase letters
> > >
> > > I've attached a patch that fixes most issues - it doesn't solve the bias
> > > towards numbers, because it's caused by requiring at-least one number per
> > > password - so in an 8 character password there'd have to be 0.1 numbers to
> > > avoid bias. There's an argument to be made for removing the at-least-one
> > > rule, but if the system that password is being used with has those rules,
> > > it doesn't fix the problem anyway. Perhaps a separate flag for that?
> > >
> > > The changes are:
> > >
> > > - Print a message and abort() of there's trouble opening or reading
> > > /dev/urandom (So apport should pick up any packages that have been using
> > > insecure entropy)
> > > - Make "-s" the default
> > > - Add an argument --insecure-phonemes (or -P)
> > > - Non-tty passwords are now as secure as tty
> > > - Require lower-case characters be present to even out some bias
> > > - Pull in passwdqc as a Suggests on the debian package - pwqgen can
> > > generate sane random passphrases
> > >
> > > I can't imagine any reasonable use-case for the non-tty defaults (except
> > > maybe combining with espeak as an enhanced interrogation technique), and
> > > you can be certain that there's some people out there with it embedded in a
> > > script that's generating useless passwords.
> > >
> > > For phonemes mode in general, the bias is extreme, there are a limited
> > > number of possible combinations and it is generally not suitable for
> > > security purposes. I have some fairly detailed analysis of it, but I
> > > believe this list has a no-exploits policy...
> > >
> > > Regards,
> > > Michael
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