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Date: Fri, 3 Nov 2017 13:01:10 +0100
From: Jakub Wilk <>
Subject: Re: Security risk of server side text editing in
 general and vim.tiny specifically

* Fiedler Roman <>, 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].


Jakub Wilk

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