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

A new set of mode 6 vulnerabilities has been discovered and, while these vulnerabilities can be reduced by making sure you have restrict default … noquery in your ntp.conf file, the best and most complete way to avoid these vulnerabilities is to install and deploy ntp-4.2.8 which was released on 18 December 2014.

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

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Are you using Autokey in production? If so, please contact Harlan - he's got some questions for you.

5.1. NTP Access Policy

It was proposed on news://comp.protocols.time.ntp to publish the access policy for ntp via ntp/tcp. Since ntp (the time protocol) only uses ntp/udp, ntp/tcp is available as a reserved port number for ntp.

It would be possible to publish both a machine readable version (in some standard format, to be determined) and a human readable version.

A simple solution is to use inetd to offer a file on connection to ntp/tcp. Example line in inetd.conf:

ntp  stream  tcp     nowait  nobody  /usr/libexec/tcpd       /bin/cat /etc/ntp-access-policy.txt

The file /etc/ntp-access-policy.txt would then contain the access policy.

-- KoosVanDenHout - 28 Aug 2003