Univention Corporate Server 4.0 erratum 212 (security)

These vulnerabilities have been fixed in ntp:
* Man-in-the-middle attackers may spoof packets by omitting the MAC
  because the symmetric-key feature in the receive function in
  ntp_proto.c requires a correct MAC only if the MAC field has a
  nonzero length (CVE-2015-1798)
* Man-in-the-middle attackers may cause a denial of service
  (synchronization loss) by spoofing the source IP address of a peer
  because the symmetric-key feature in the receive function in
  ntp_proto.c performs state-variable updates upon receiving certain
  invalid packets (CVE-2015-1799)