The panic_gate check in NTP before 4.2.8p5 is only re-enabled after the first change to the system clock that was greater than 128 milliseconds by default, which allows remote attackers to set NTP to an arbitrary time when started with the -g option, or to alter the time by up to 900 seconds otherwise by responding to an unspecified number of requests from trusted sources, and leveraging a resulting denial of service (abort and restart).
http://aix.software.ibm.com/aix/efixes/security/ntp_advisory5.asc
http://lists.fedoraproject.org/pipermail/package-announce/2015-November/170684.html
http://lists.fedoraproject.org/pipermail/package-announce/2015-November/170926.html
http://lists.fedoraproject.org/pipermail/package-announce/2016-February/177507.html
http://lists.opensuse.org/opensuse-security-announce/2016-04/msg00059.html
http://lists.opensuse.org/opensuse-security-announce/2016-04/msg00060.html
http://lists.opensuse.org/opensuse-security-announce/2016-05/msg00020.html
http://lists.opensuse.org/opensuse-security-announce/2016-05/msg00038.html
http://lists.opensuse.org/opensuse-security-announce/2016-05/msg00048.html
http://lists.opensuse.org/opensuse-security-announce/2016-07/msg00026.html
http://lists.opensuse.org/opensuse-security-announce/2016-08/msg00042.html
http://lists.opensuse.org/opensuse-updates/2016-05/msg00114.html
http://rhn.redhat.com/errata/RHSA-2015-1930.html
https://bugzilla.redhat.com/show_bug.cgi?id=1271076
http://seclists.org/bugtraq/2016/Feb/164
https://ics-cert.us-cert.gov/advisories/ICSA-15-356-01
https://security.netapp.com/advisory/ntap-20171004-0001/
https://support.citrix.com/article/CTX220112
https://www-01.ibm.com/support/docview.wss?uid=isg3T1023885
https://www-01.ibm.com/support/docview.wss?uid=isg3T1024073
https://www-01.ibm.com/support/docview.wss?uid=nas8N1021264
https://www-01.ibm.com/support/docview.wss?uid=ssg1S1005821
https://www-01.ibm.com/support/docview.wss?uid=swg21979393
https://www-01.ibm.com/support/docview.wss?uid=swg21980676
https://www-01.ibm.com/support/docview.wss?uid=swg21983501
https://www-01.ibm.com/support/docview.wss?uid=swg21983506
https://www.freebsd.org/security/advisories/FreeBSD-SA-16:02.ntp.asc
https://www.ibm.com/support/home/docdisplay?lndocid=migr-5099428
https://www.oracle.com/technetwork/topics/security/bulletinjan2016-2867206.html
https://www.oracle.com/technetwork/topics/security/linuxbulletinoct2015-2719645.html
http://www.debian.org/security/2015/dsa-3388
http://www.oracle.com/technetwork/security-advisory/cpujul2016-2881720.html