Follow @Openwall on Twitter for new release announcements and other news
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Wed, 24 Sep 2014 15:12:08 -0400
From: Chet Ramey <>
To: Michal Zalewski <>,
Subject: Re: CVE-2014-6271: remote code execution through bash

On 9/24/14, 2:54 PM, Michal Zalewski wrote:
>> My main concern with the current patch is that still exposes the bash parser
>> and function definition printer to attacks from the network. Bugs in those
>> fairly large components could cause another critical issue.
> Yup, that surprised me when testing the patch, too - I can still get a
> function called HTTP_COOKIE, for example. I worry about potential side
> effects of parsing even in absence of parser bugs. In most
> object-oriented languages, such side effects are practically
> guaranteed. Bash may be saved by simplicity, but not sure how robust
> that assumption is.

Lots of code out there uses exported functions.

> I've written more code in bash than I should have and never used
> function exports, or even realized that they exist. I wonder if they
> can be made optional (e.g., gated by a flag on the subprocess) without
> breakage.
> Another option may be to export them through specially prefixed
> variables, which should be transparent but minimize the risk of
> interfering with web servers and such.

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.

The leading candidates both raise the bar by requiring a potential
attacker to be able to create arbitrarily-named environment variables as
well as environment variables with specific values.

I considered (and implemented) a blacklist approach that would have
protected against a set of commonly-named variables (HTTP_*, CGI_*,
SSH_*, LC_*, and so on), but the consensus was that that was too easily
circumvented.  I removed it from the distributed patches.


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

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.