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Date: Fri, 3 Nov 2017 12:25:12 +0000
From: Fiedler Roman <>
To: "''" <>
Subject: Re: Security risk of server side text editing in
 general and vim.tiny specifically

> From: Jakub Wilk []
> * 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?

This is one of the attack points, but there are multiple sequences of 
problematic syscalls, especially when running vim.tiny as root, also

getxattr("x.txt", "system.posix_acl_access", ... -> get attrs of arbitrary 
file via symlink
setxattr("x.txt", "system.posix_acl_access",  ... -> set those attrs on 
arbitrary file
chmod("x.txt", 0100644)                 = 0   -> set mode of previous x.txt on 
arbitrary file

As previously stated, this indicates, that the 
"root-edits-file-of-non-root-user" use case was not considered. But is that a 

Put it another way: when a doctor cuts himself with his scalpel, is it the 
doctor's or the scalpel's fault?

LG Roman

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