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Date: Mon, 06 Oct 2014 18:58:12 +0200
From: Florian Weimer <fweimer@...hat.com>
To: oss-security@...ts.openwall.com
Subject: Re: Healing the bash fork
On 09/30/2014 05:02 PM, Mark R Bannister wrote:
> Glad my over-simplified example has raised a few smirks. Now for a slightly less simplified version:
>
> putenv("PATH=/bin:/usr/bin");
> setreuid(0, 0);
> system("date");
>
> But the point is I've tried to boil down a relatively complex program by studying endless strace outputs to attempt to demonstrate a real world exploit. It wasn't actually "date" that was being called, but you get the point.
>
> In the past, i.e. pre-Shellshock, the above code may have raised eyebrows, but as PATH was sanitised it would have passed numerous security audits.
I doubt that (or more realistically, I hope it's not true). Even the
1996 edition of “Practical UNIX and Internet Security” mentions that you
have to reset IFS as well (a significant omission if “at” does something
even if it hasn't received any parameters). The authors also point out
that putenv and setenv may only replace the first occurrence of an
environment variable in the environ array, while the system shell could
well pick up the last occurrence.
--
Florian Weimer / Red Hat Product Security
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