fusermount in FUSE before 2.9.3-15 does not properly clear the environment before invoking (1) mount or (2) umount as root, which allows local users to write to arbitrary files via a crafted LIBMOUNT_MTAB environment variable that is used by mount's debugging feature.
https://www.exploit-db.com/exploits/37089/
https://twitter.com/taviso/status/601370527437967360
https://security.gentoo.org/glsa/201701-19
https://security.gentoo.org/glsa/201603-04
http://www.ubuntu.com/usn/USN-2617-3
http://www.ubuntu.com/usn/USN-2617-2
http://www.ubuntu.com/usn/USN-2617-1
http://www.securitytracker.com/id/1032386
http://www.securityfocus.com/bid/74765
http://www.debian.org/security/2015/dsa-3268
http://www.debian.org/security/2015/dsa-3266
http://packetstormsecurity.com/files/132021/Fuse-Local-Privilege-Escalation.html
http://lists.opensuse.org/opensuse-updates/2015-06/msg00007.html
http://lists.opensuse.org/opensuse-updates/2015-06/msg00005.html
http://lists.fedoraproject.org/pipermail/package-announce/2015-June/160106.html
http://lists.fedoraproject.org/pipermail/package-announce/2015-June/160094.html
http://lists.fedoraproject.org/pipermail/package-announce/2015-June/159831.html
http://lists.fedoraproject.org/pipermail/package-announce/2015-June/159683.html
http://lists.fedoraproject.org/pipermail/package-announce/2015-June/159543.html
http://lists.fedoraproject.org/pipermail/package-announce/2015-June/159298.html