In commit 1c851cbe0c562894bd38c0f9f39d12be306b3e59 I added a patch
to the shadow package that fixes CVE-2017-2616 in `su`.

This bug makes it possible for any local user to send SIGKILL to other
processes with root privileges. For example, you could use this bug to
make another user's screen locker exit.

It is recommended to update your GuixSD systems, since shadow provides
`su` on GuixSD.

More information:

https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-2616
http://seclists.org/oss-sec/2017/q1/490
http://seclists.org/oss-sec/2017/q1/474
https://github.com/shadow-maint/shadow/commit/08fd4b69e84364677a10e519ccb25b71710ee686

I also fixed the bug in util-linux by grafting this patch:

https://github.com/karelzak/util-linux/commit/dffab154d29a288aa171ff50263ecc8f2e14a891