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NTP clock variables information disclosure

Severity CVSS Published Added Modified
1 (AV:N/AC:L/Au:N/C:N/I:N/A:N) May 06, 2009 April 01, 2011 March 19, 2014


This sytem allows the internal NTP variables to be queried. These variables contain potentially sensitive information, such as the NTP software version, operating system version, peers, and more.

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  • Disable NTP readvar queries

    Apply a restrict option to all hosts that are not authorized to perform NTP readvar queries. For example, to deny readvar requests from all clients, put the following in the NTP configuration file, typically /etc/ntp.conf, and restart the NTP service:

          restrict default mask noquery 

  • Cisco

    Restrict NTP readvar queries

    Apply an ACL that restricts NTP readvar queries from unauthorized clients, as described in the 'Configuring NTP Access Restrictions' section of the Cisco IOS documentation.

    Alternatively, if NTP is not required, disable it entirely by running the following command:

          ntp disable