arch/x86/entry/entry_64.S in the Linux kernel before 4.1.6 on the x86_64 platform improperly relies on espfix64 during nested NMI processing, which allows local users to gain privileges by triggering an NMI within a certain instruction window.
https://www.exploit-db.com/exploits/37722/
https://github.com/torvalds/linux/commit/9b6e6a8334d56354853f9c255d1395c2ba570e0a
https://bugzilla.redhat.com/show_bug.cgi?id=1243465
http://www.ubuntu.com/usn/USN-2691-1
http://www.ubuntu.com/usn/USN-2690-1
http://www.ubuntu.com/usn/USN-2689-1
http://www.ubuntu.com/usn/USN-2688-1
http://www.ubuntu.com/usn/USN-2687-1
http://www.securityfocus.com/bid/76004
http://www.openwall.com/lists/oss-security/2015/08/04/8
http://www.openwall.com/lists/oss-security/2015/07/22/7
http://www.kernel.org/pub/linux/kernel/v4.x/ChangeLog-4.1.6
http://www.debian.org/security/2015/dsa-3313
http://lists.opensuse.org/opensuse-security-announce/2015-08/msg00011.html