[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Message-ID: <20170406083928.GE32355@suse.de>
Date: Thu, 6 Apr 2017 10:39:28 +0200
From: Marcus Meissner <meissner@...e.de>
To: oss-security@...ts.openwall.com
Subject: Re: libxslt math.random issue
On Thu, Apr 06, 2017 at 10:32:45AM +0200, Hanno Böck wrote:
> 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.).
It is a bit tricky to find out. I googled some use-cases.
- UUID generation was looked for by 1 stackoverflow user
- some harmless randomness in XSLT conversion for selection random pictures
> 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)
it should be fd != -1 , my bad :/
Ciaop, Marcus
Powered by blists - more mailing lists
Please check out the
Open Source Software Security Wiki, which is counterpart to this
mailing list.
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
