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Date: Thu, 13 Jun 2013 02:56:34 +0400
From: Solar Designer <solar@...nwall.com>
To: oss-security@...ts.openwall.com
Cc: john-users@...ts.openwall.com
Subject: Re: [oss-security] CVE request: WordPress 3.5.1 denial of service vulnerability
On Thu, Jun 13, 2013 at 12:05:14AM +0400, Alexander Cherepanov wrote:
> On 2013-06-12 17:11, Solar Designer wrote:
> >Arguably, library code should reject the most insane parameter values.
> >For example, musl libc - http://www.musl-libc.org - version 0.9.10
> >rejects bcrypt's log2(cost)> 19 and limits SHA-crypt's rounds count
> >to< 10M for this reason (original SHA-crypt limits to< 1 billion).
>
> On a related note: shouldn't John the Ripper also reject hashes with
> insane run-time or memory cost parameters?
I don't have strong feelings one way or the other, which is why I
haven't implemented this so far. Also, in JtR we did not support any
hashes/ciphers with configurable memory cost until very recently, so
that part of the issue did not arise. As to processing time cost, in
JtR it's at worst a DoS against a cracking run, which the user would
notice and hopefully deal with. Yes, having some warnings printed could
help pinpoint the culprit hashes - we can add that. As to the memory
usage issue, maybe we need to have a configurable total memory limit (in
john.conf) - not a per-hash limit. We could use RLIMIT_AS (or the like)
where supported. It's more reliable than doing our own memory usage
tracking, although then we'd need to ensure we're able to print a
sensible error message when that limit is almost reached (this is not
difficult, it's just something not to overlook).
Alexander
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