From Ted Unangst@21:1/5 to All on Fri Jul 15 14:55:02 2016
In addition to the patched bugs, several panics were discovered by NCC that
can be triggered by root or users with the usermount option set. These bugs
are not getting patched because we believe they are only the tip of the iceberg. The mount system call exposes too much code to userland to be considered secure.
As remediation, it's recommended to disable usermount. For the forthcoming 6.0 release, the usermount option will be removed.