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Date: Tue, 31 Oct 2017 13:50:36 +0100
From: Stefan B├╝hler <stbuehler@...httpd.net>
To: oss-security@...ts.openwall.com
Subject: Re: Fw: Security risk of vim swap files

On 10/31/2017 01:37 PM, Solar Designer wrote:
> On Tue, Oct 31, 2017 at 01:23:52PM +0100, Hanno B??ck wrote:
>> I think vim should change the behavior of swap files:
>> 1. they should be stored in /tmp by default
>> 2. they should have secure permissions (tmp file security is
>> a tricky thing and needs careful consideration to avoid symlink attacks
>> and the like, but there are dedicated functions for this like mkstemp).
>> 3. Ideally they also shouldn't leak currently edited filenames (e.g.
>> they shouldn't be called /tmp/.test.txt.swp, but more something
>> like /tmp/.vim_swap.123782173)
> 
> Out of these, I think only 2 should be done: the files should be mode
> 0600 or 0400 even if the original file's permissions and/or the umask
> are more relaxed.
> 
> 1 and 3 go against intended use for these files - recovery of an edit in
> progress if the editor or the entire system crashes (and comes back up
> e.g. after a power-cycle).  /tmp contents might not survive a reboot,
> and randomized filenames would prevent vim itself from detecting the
> problem and offering recovery, which it does now.

You could keep the .test.txt.swp file, but make it a symlink and encode
information where to find the real swap file (/var/tmp/, /tmp, ...) in
the symlink.

It shouldn't link directly to the swap file, but perhaps look like
"swap:///var/tmp/.vim_swap.random_id".

Instead of a symlink you could of course just create a normal text file
with the real swap filename in it, but then it might be easier for an
attacker to find the real filename and read that file.

cheers,
Stefan

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