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Date: Thu, 25 Sep 2014 11:37:45 -0400
From: Chet Ramey <>
To: Solar Designer <>
Subject: Re: CVE-2014-6271: remote code execution through bash

On 9/24/14, 10:47 PM, Solar Designer wrote:
> On Wed, Sep 24, 2014 at 03:12:08PM -0400, Chet Ramey wrote:
>> There are several options for making shell functions inherited via the
>> environment more robust, none of them backwards compatible.  I will
>> choose one and implement it for a future bash version.
> While we're at it, I think it's preferable not to output error messages
> triggerable by untrusted input, e.g.:
> $ ssh -o 'rsaauthentication yes' 0 '() { ignored; }; /usr/bin/id' 
> bash: warning: SSH_ORIGINAL_COMMAND: ignoring function definition attempt
> bash: error importing function definition for `SSH_ORIGINAL_COMMAND'
> (as seen with the current bash patches).  This might be unnecessarily
> revealing or/and it might confuse whatever other program was invoking
> something via bash, resulting in attacker-triggerable unintended
> behavior in that caller program.  Yes, there are numerous other error
> conditions anyway - such as running out of memory - which may result in
> messages printed to stderr.  Yet we might want to avoid printing error
> messages for environment variable value parsing errors (ideally, we'd
> avoid the parsing itself as well), unless a debugging or a verbose mode
> is enabled locally (in a way that can't realistically be triggered via
> an unsuspecting network service).

I disagree.  It's important for a program -- not just the shell -- to tell
the user when it attempts to do something on his behalf and is unable to
do it.


``The lyf so short, the craft so long to lerne.'' - Chaucer
		 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRU

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