Security Advisory

NTP - CVE-2020-11868
Published: July 27, 2020
Last Update: August 16, 2021

In March, 2020, NTP.org[1] released a security advisory detailing a number of security issues. The following vulnerability reported in the NTP advisory is addressed in this document.

Item Score
# Vulnerability ID Source Score Summary
1 CVE-2020-11868 CVSS 3.0 7.5 High ntp: DoS on client ntpd using server mode packet [2]
Affected Releases

The table below indicates releases of ACOS exposed to these vulnerabilities and ACOS releases that address these issues or are otherwise unaffected by them.

Customers using affected ACOS releases can overcome vulnerability exposures by updating to the indicated resolved release. If the table does not list a corresponding resolved or unaffected release, then no ACOS release update is currently available.

Releases Affected Releases Resolved or Unaffected
5.2.0 5.2.0-P1
5.0.0 – 5.1.0-P4 5.1.0-P5
4.1.4 – 4.1.4-GR1-P4 4.1.4-GR1-P5
4.1.2 – 4.1.2-P1 4.1.4-GR1-P5
4.1.1 – 4.1.1-P13 4.1.4-GR1-P5
4.1.100 – 4.1.100-P7 None
4.1.0 – 4.1.0-P13 4.1.4-GR1-P5
3.1.0-P1 – 3.2.5-P1 3.2.5-P2, 5.0.1-TPS
2.8.2 – 2.8.2-P10 4.1.4-GR1-P5
2.7.2 – 2.7.2-P16 4.1.4-GR1-P5
Workarounds and Mitigations

Common security best practices in the industry for network appliance management and control planes can enhance protection against remote malicious attacks. Limit the exploitable attack surface for critical, infrastructure, networking equipment through the use of access lists or firewall filters to and from only trusted, administrative networks or hosts.

Ensure that the following are included for NTP configuration for ACOS devices:

  • Use authentication with symmetric keys. This approach applies a symmetric key for the calculation of the MAC, which protects authenticity and integrity of the exchanged packets for an association. It is recommended that each association be protected by its own unique key.
  • Maximize the number of time sources configured and their availability. ACOS supports a maximum of 4 NTP servers, which will provide sufficient backup in the event that one source goes down.
Software Updates

Software updates that address these vulnerabilities are or will be published at the following URL:

Vulnerability Details

The following table shares brief descriptions of the vulnerabilities addressed in this document.

Vulnerability ID Vulnerability Description

ntpd in ntp before 4.2.8p14 and 4.3.x before 4.3.100 allows an off-path attacker to block unauthenticated synchronization via a server mode packet with a spoofed source IP address, because transmissions are rescheduled even when a packet lacks a valid origin timestamp.



Modification History
Revision Date Description
1.0 July 27, 2020

Initial Publication

2.0 August 16, 2021

x Add resolved releases for 3.2.5

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