chrony before 1.31.1 does not properly protect state variables in authenticated symmetric NTP associations, which allows remote attackers with knowledge of NTP peering to cause a denial of service (inability to synchronize) via random timestamps in crafted NTP data packets.
Source: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2015-1853
Reference (s):
- http://chrony.tuxfamily.org/News.html
- https://security.gentoo.org/glsa/201507-01