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Date: Thu, 25 Sep 2014 20:05:33 +0400
From: Solar Designer <solar@...nwall.com>
To: oss-security@...ts.openwall.com
Cc: chet.ramey@...e.edu
Subject: Re: CVE-2014-6271: remote code execution through bash
On Thu, Sep 25, 2014 at 04:17:31PM +0100, John Haxby wrote:
> There seems to be a wider issue even when we have well-formed functions
> coming in, for example,
>
> env rm='() { echo will not; }' bash -c 'rm core'
John first brought this aspect up on the private distros list, but I
asked for it to be moved to oss-security, which John did (thanks!)
My reply on distros was:
| It appears that right now we're only dealing with the case when the
| attacker can't specify arbitrary env var names. Attacks are limited in
| that way if performed e.g. via/on sshd forced command or httpd CGI
| interface.
|
| With an arbitrary env var, you could arguably do lots of damage anyway -
| e.g., via LD_PRELOAD. However, I think there are notable exceptions to
| this - e.g., when a sudo-like program or/and libc resets the known
| variables like LD_*, but does not use a whitelist, so things like a
| variable named "rm" (or BASH_FUNC_rm() after Florian's patch) would
| make it through a SUID exec, switching of privs to another user, and
| exec'ing a script. So, yes, there may be an issue here for some setups
| that are risky but are not necessarily exploitable otherwise.
|
| I don't know if there's any plan to deal with this issue. We really
| ought to discuss it on oss-security.
> My feeling is that if you're going to import functions from the
> environment then you should do that explicitly either through a switch
> (--import?) or a builtin that can import all or selected functions. Or
> both.
While your specific examples are not necessarily relevant, I agree that
in the long run the functionality should be restricted in a way like you
suggest.
> I worry that simply fixing CVE-2014-6271 and CVE-2014-7129 is just
> setting the scene for the next parser problem.
That's my feeling too.
At the very least, we also need Florian's patch adding a prefix and a
suffix to the variable names, although this won't be sufficient against
local attacks via existing blacklist-using sudo-like wrappers.
Our excuse is that blacklists are not a good practice anyway.
Alexander
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