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Date: Fri, 06 Jun 2014 13:12:45 +0100
From: Simon McVittie <smcv@...ian.org>
To: oss-security@...ts.openwall.com
Subject: Re: Re: [FD] Bug in bash <= 4.3 [security
 feature bypassed]

On 06/06/14 03:51, Jeffrey Walton wrote:
> It looks like Rage Against The Cage has been rediscovered. Also known
> as Android ADB Setuid bug.

It appears to be the same class of implementation error (calling
setuid() without checking whether it succeeded) in a different codebase
- analogous to the way lots of codebases have an off-by-one buffer
overflow, without off-by-one buffer overflows all being rediscoveries of
the same bug.

If something invokes bash (e.g. via system()) with untrusted input while
setuid, I would argue that that's a vulnerability in the invoking
process; the fact that bash tries to drop privileges is a hardening
measure (attempting to mitigate other projects' vulnerabilities). So I'd
characterize this as "bash had a hardening measure that doesn't work as
well as it was meant to". It's still a bug, and it would still be good
if the maintainers of bash fixed it so it could mitigate future
vulnerabilities.

In my view, setuid[1] processes are the ones doing something unusual and
risky, so the onus should be on the authors of setuid code to:

* consider whether it actually needs to be setuid
* if it does, implement it securely
* drop privileges as soon as feasible
* avoid using libraries that are not designed and documented to be
  setuid-safe, at least until after privileges have been irrevocably
  dropped

(that last point is not relevant here but is relevant in general)

    S

[1] or setgid, or setcap +ep

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