From: Daniel Shahaf <d.s@daniel.shahaf.name>
To: Bart Schaefer <schaefer@brasslantern.com>
Cc: zsh-workers@zsh.org
Subject: Re: zsh/files module and insecure tempfile creation
Date: Mon, 12 Jan 2015 05:43:44 +0000 [thread overview]
Message-ID: <20150112054344.GC1728@tarsus.local2> (raw)
In-Reply-To: <150109223150.ZM24107@torch.brasslantern.com>
Bart Schaefer wrote on Fri, Jan 09, 2015 at 22:31:50 -0800:
> I'm trying to work through the "attack vector" for the mv -f trick.
> The situation is that a script wants to create a plain empty file
> with a known name, let's say "/tmp/zsh12345".
>
> If the attacker creates his own plain file named /tmp/zsh12345 then the
> "mv -f" will clobber it, so that's not at issue. Therefore an attack
> is possible if the attacker can create a directory (or symlink to a
> directory) named /tmp/zsh12345 and writable by the zsh process,
> because then mv will put the empty plain file inside that directory.
>
> Next the attacker must be able to swap the directory or symlink with
> a symlink to his own target file. Presumably if he could create it
> in the first place, he can swap it. So we do have an attack that can
> clobber any file writable by the zsh user. Anybody disagree?
On FreeBSD systems, 'cat /path/to/dir' works (prints something and
returns 0). Therefore, even if the (symlink-to-)dir is not replaced by
a file, unexpected effects might be caused when some code attempts to
cat the tempfile (which is in fact a directory) — whether in order to
run it as shell commands or in order to use it as data.
Sorry, but I haven't audited the patch to see what exactly this could
cause in each instance. (No time.)
Daniel
next prev parent reply other threads:[~2015-01-12 5:53 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-01-10 6:31 Bart Schaefer
2015-01-10 19:58 ` Peter Stephenson
2015-01-11 2:04 ` Bart Schaefer
2015-01-12 5:43 ` Daniel Shahaf [this message]
2015-01-12 6:56 ` Bart Schaefer
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