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Date: Fri, 26 Sep 2014 13:41:45 +0100
From: "Mark R Bannister" <mark@...seconsulting.co.uk>
To: oss-security@...ts.openwall.com
Subject: Re: Re: CVE-2014-6271: remote code execution through bash (3rd vulnerability)
Arguments that people shouldn't have setuid shell scripts don't stack up, because even if you write your setuid program in some other language, you might unwittingly exec something written in bash.
As /bin/sh is symlinked to /bin/bash in RHEL, the moment you call out to the system to do a piece of work for you, you're at risk of invoking bash and thereby being vulnerable to a root exploit. For example:
$ env bzip2='() { echo vulnerable >&2; }' /usr/bin/bzdiff /tmp/file1.bz /tmp/file2.bz
$ env test='() { echo vulnerable >&2; }' /usr/bin/ldd /usr/bin/gcc
So this is not about whether or not someone has written a setuid shell script. This has uncovered a potential new exploit for any setuid program. Indeed the very first setuid program that I discovered this exploit with was a binary (compiled C program) that happened to exec ldd while it was running.
I don't think this issue can be swept under the carpet.
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