OpenBSD 5.8 and 5.9 allows certain local users with kern.usermount privileges to cause a denial of service (kernel panic) by mounting a tmpfs with a VNOVAL in the (1) username, (2) groupname, or (3) device name of the root node.
http://www.securityfocus.com/bid/91805
http://www.openwall.com/lists/oss-security/2016/07/14/5