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Message-ID: <20170406103245.67949bfc@pc1>
Date: Thu, 6 Apr 2017 10:32:45 +0200
From: Hanno Böck <hanno@...eck.de>
To: oss-security@...ts.openwall.com
Subject: Re: libxslt math.random issue
Hi,
On Thu, 6 Apr 2017 07:44:00 +0200
Marcus Meissner <meissner@...e.de> wrote:
> CVE-2015-9019 has been assigned to use of libexslt (in libxslt) usage
> of "math.random" without initializing the randomseed.
>
> https://bugzilla.gnome.org/show_bug.cgi?id=758400
> https://bugzilla.suse.com/show_bug.cgi?id=934119
I have some questions and comments:
1. What's the use of the random number and what's the security impact
if it's not random? That's not explained
In case of the bugreport.
In case a cryptographically secure random number is required then using
rand()/srand() is a bad idea anyway.
(Unfortunately there's no secure random in the standard libc, but at
least glibc now has getrandom.).
2. This part of the patch looks a bit strange:
+ seed = time(NULL); /* just in case /dev/urandom is not there */
+ if (fd == -1) {
+ read (fd, &seed, sizeof(seed));
+ close (fd);
+ }
You're calling time() unconditionally, although it's kinda just a
fallback. Why not
+ if (fd == -1) {
+ read (fd, &seed, sizeof(seed));
+ close (fd);
+ } else {
+ seed = time(NULL);
+ }
?
(obviously using time is not a secure way to do random numbers, if
secure numbers are required cross-plattform you need to do this
otherwise anyway)
--
Hanno Böck
https://hboeck.de/
mail/jabber: hanno@...eck.de
GPG: FE73757FA60E4E21B937579FA5880072BBB51E42
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