The do_umount function in fs/namespace.c in the Linux kernel through 3.17 does not require the CAP_SYS_ADMIN capability for do_remount_sb calls that change the root filesystem to read-only, which allows local users to cause a denial of service (loss of writability) by making certain unshare system calls, clearing the / MNT_LOCKED flag, and making an MNT_FORCE umount system call.
https://access.redhat.com/errata/RHSA-2017:1842
https://access.redhat.com/errata/RHSA-2017:2077
https://bugzilla.redhat.com/show_bug.cgi?id=1151108
http://secunia.com/advisories/60174
http://secunia.com/advisories/61145
http://secunia.com/advisories/62633
http://secunia.com/advisories/62634
https://exchange.xforce.ibmcloud.com/vulnerabilities/96994
http://www.openwall.com/lists/oss-security/2014/10/08/22
http://www.securitytracker.com/id/1031180
http://www.ubuntu.com/usn/USN-2415-1
http://www.ubuntu.com/usn/USN-2416-1
http://www.ubuntu.com/usn/USN-2417-1
http://www.ubuntu.com/usn/USN-2418-1
http://www.ubuntu.com/usn/USN-2419-1