[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20120712140359.GB5098@suse.de>
Date: Thu, 12 Jul 2012 16:04:00 +0200
From: Marcus Meissner <meissner@...e.de>
To: oss-security@...ts.openwall.com
Subject: Re: CVE Request: Overflow fix in bash 4.2 patch 33
On Wed, Jul 11, 2012 at 11:29:22AM -0600, Kurt Seifried wrote:
> On 07/11/2012 10:15 AM, Marcus Meissner wrote:
> > Hi,
> >
> > the bash maintainer kindly mailed us and other vendors a
> > notification of a overflow in the bash "test" builtin when
> > "/dev/fd/..." filenames are used.
> >
> > ftp://ftp.gnu.org/pub/gnu/bash/bash-4.2-patches/bash42-033
> >
> > Reproducer: test -e /dev/fd/111111111111111111111111111111111
> >
> > Problem is caught by -D_FORTIFY_SOURCE=2 if enabled, and likely
> > also by -fstack-protector (not tested)
> >
> > Goes all the way back to old bashes.
> >
> > The likeliness of people able to inject those filenames into shell
> > scripts and not being able to execute shellcode themselves is
> > however slim. (setuid root shell scripts are not possible.)
> >
> > Security (CVE) relevant scenario we thought of is breaking out of
> > a restricted shell mode.
> >
> > Ciao, Marcus
>
> Can you give a more concrete example, e.g. you're talking about
> http://www.gnu.org/software/bash/manual/html_node/The-Restricted-Shell.html
> I assume? Are we simply talking about violating those restrictions?
Yes. Breaking out of the restricted shell using this issue.
$ bash -r
bash: /dev/pts/9: Gesperrt: Die Ausgabe darf nicht umgeleitet werden.
$ test -f /dev/fd/111111111111111111111111111111111111111111111111111111111111111
*** buffer overflow detected ***: bash terminated
...
So basically without fortification measures you can inject a ASCII based
shell-code to execute code you shouldn't.
(One can argue that of how secure you evaluate restricted shells ...)
Ciao, 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.
