full-disclosure - Re: tar alternative

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Date: Wed, 20 Sep 2006 13:37:22 -0700
From: Jon Hart <jhart@...ofed.org>
To: Tim <tim-security@...tinelchicken.org>
Cc: full-disclosure@...ts.grok.org.uk
Subject: Re: tar alternative

On Wed, Sep 20, 2006 at 03:53:06PM -0400, Tim wrote:
> Well, the whole idea that having to use a non-root account to unpack
> some files has always been rediculous to me.  Sure, given the way tar
> behaves, it is insane not to, but for a software distribution tool,
> making this a requirement is pretty lame.  Changing tar's behavior to be
> safer is possible, but would likely degrade the ability of tar to be a
> good backup tool.  The use cases for each type of tool are simply
> different.

I've been following this since it started, but never actually looked
into how to make tar "safer" or if there is a better alternative out
there.

Think of some of the risks here.  tar archives that unpack into . or
../../../some/sensitive/dir -- raise your hand if you've been bit by
this.  I was, once, and ever since tar -ztvf all the archives I handle
before actually unpacking.  Doing a pentest and need some usernames?
Crawl for .tar.* and parse out the usernames.

One option here is to use the --numeric-owner options, or better yet,
the --owner and --group option:

$  tar --numeric-owner -cvf - foo |tar -tvf -
foo
-rw-r--r-- 1000/1000         0 2006-06-30 15:19 foo

$  tar --owner 65535 --group 65535  -cvf - foo |tar -tvf -
foo
-rw-r--r-- 65535/65535       0 2006-06-30 15:19 foo

Obviously, this only solves part of the problem.

-jon

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