NTP users are strongly urged to take immediate action to ensure that their NTP daemons are not susceptible to being used in distributed denial-of-service (DDoS) attacks. Please also take this opportunity to defeat denial-of-service attacks by implementing Ingress and Egress filtering through BCP38.

ntp-4.2.8p15 was released on 23 June 2020. It addresses 1 medium-severity security issue in ntpd, and provides 13 non-security bugfixes over 4.2.8p13.

Please see the NTP Security Notice for vulnerability and mitigation details.

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NTP Bug 3454

Unauthenticated packet can reset authenticated interleaved association

• Date Resolved: Stable (4.2.8p11) 27 Feb 2018
• References: Sec 3454 / CVE-2018-7185 / VU#961909
• Affects: ntp-4.2.6, up to but not including ntp-4.2.8p11.
• CVSS2: MED 4.3 (AV:N/AC:M/Au:N/C:N/I:N/A:P) This could score between 2.9 and 6.8.
• CVSS3: LOW 3.1 CVSS:3.0/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L This could score between 2.6 and 3.1
• Summary: The NTP Protocol allows for both non-authenticated and authenticated associations, in client/server, symmetric (peer), and several broadcast modes. In addition to the basic NTP operational modes, symmetric mode and broadcast servers can support an interleaved mode of operation. In ntp-4.2.8p4 a bug was inadvertently introduced into the protocol engine that allows a non-authenticated zero-origin (reset) packet to reset an authenticated interleaved peer association. If an attacker can send a packet with a zero-origin timestamp and the source IP address of the "other side" of an interleaved association, the 'victim' ntpd will reset its association. The attacker must continue sending these packets in order to maintain the disruption of the association. In ntp-4.0.0 thru ntp-4.2.8p6, interleave mode could be entered dynamically. As of ntp-4.2.8p7, interleaved mode must be explicitly configured/enabled.
• Mitigation:
  • Implement BCP-38.
  • Upgrade to 4.2.8p11, or later, from the NTP Project Download Page or the NTP Public Services Project Download Page.
  • If you are unable to upgrade to 4.2.8p11 or later and have peer HOST xleave lines in your ntp.conf file, remove the xleave option.
  • Have enough sources of time.
  • Properly monitor your ntpd instances.
  • If ntpd stops running, auto-restart it without -g .
• Credit: This weakness was discovered by Miroslav Lichvar of Red Hat.

Reported: 24 Jan 2018