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Date: Fri, 3 Nov 2017 13:01:10 +0100
From: Jakub Wilk <jwilk@...lk.net>
To: oss-security@...ts.openwall.com
Subject: Re: Security risk of server side text editing in
general and vim.tiny specifically
* Fiedler Roman <Roman.Fiedler@....ac.at>, 2017-11-03, 11:07:
>POC for vim.tiny on Ubuntu Xenial to overwrite arbitrary files as user
>root when editing file in directory owned by other user is available on
>request, disclosure after one week or if list discussion indicates
>other timing.
By default[1], when vim wants to overwrite the file "foo", it does:
rename("foo", "foo~") = 0
open("foo", O_WRONLY|O_CREAT|O_TRUNC|O_LARGEFILE, 0600) = 3
There's a race window between the two syscalls when the attacker could
re-create "foo", and then vim would happily write to it.
Is this the attack you meant?
NB, vim disables this behavior for files in /tmp (but not /var/tmp)[2].
[1] http://vimdoc.sourceforge.net/htmldoc/options.html#%27writebackup%27
[2] http://vimdoc.sourceforge.net/htmldoc/options.html#%27backupskip%27
--
Jakub Wilk
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