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Date: Thu, 12 Jul 2012 10:55:12 -0600
From: Kurt Seifried <kseifried@...hat.com>
To: oss-security@...ts.openwall.com
CC: Marcus Meissner <meissner@...e.de>
Subject: Re: CVE Request: Overflow fix in bash 4.2 patch 33

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On 07/12/2012 08:04 AM, Marcus Meissner wrote:
> 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

Please use CVE-2012-3410 for this issue. The --restricted stuff is
advertised as a security measure and this can be used to bypass it, so
it gets a CVE.



- -- 
Kurt Seifried Red Hat Security Response Team (SRT)
PGP: 0x5E267993 A90B F995 7350 148F 66BF 7554 160D 4553 5E26 7993



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