This was reported by gentoo to vendor-sec

Ciaran McCreesh, our Gentoo vim maintainer, found and reported upstream
several modeline-related vulnerabilities in vim :

------------------------------------------------------------
It's possible to do some pretty nasty stuff via vim modelines despite
the existing security code.

For example, by passing evil values for a fileformat setting in a
modeline, it's possible to make vim source arbitrary scripts upon
startup. This would hurt on a multiuser system. Here's one way:

User 'fred' creates a file in /home/fred/evil.vim containing lots of
nastiness (for example, "system('echo alias vim=emacs >> ~/.bashrc') |
quit"). He then creates a file in some shared location with a modeline
which does something like"set ft=../../../*fred/evil". User 'joe', who
has ftplugins and modelines enabled, edits this file. This results in a
call of ":runtime!../../../*fred/evil" , which (assuming ~/.vim is in
runtimepath) expands to ~/.vim/../../../*fred/evil which matches
/home/fred/evil.vim.
------------------------------------------------------------

Bram Moolenaar provided the following vim patch, that fixes the reported
vulnerabilities and adds more conservative modeline rights :

------------------------------------------------------------
Patch 6.3.045
Problem:   Unusual characters in an option value may cause unexpected
           behavior, especially for a modeline. (Ciaran McCreesh)
Solution:  Don't allow setting termcap options or 'printdevice' or
           'titleold' in a modeline.  Don't list options for "termcap"
           and "all" in a modeline.  Don't allow unusual characters in
           'filetype', 'syntax', 'backupext', 'keymap', 'patchmode' and
           'langmenu'.
Files:     src/option.c, runtime/doc/options.txt