NTP: Traffic amplification

Background

NTP is a protocol designed to synchronize the clocks of computers over a network. The net-misc/ntp package contains the official reference implementation by the NTP Project.

Description

ntpd is susceptible to a reflected Denial of Service attack. Please review the CVE identifiers and references below for details.

Impact

An unauthenticated remote attacker may conduct a distributed reflective Denial of Service attack on another user via a vulnerable NTP server.

Workaround

We modified the default ntp configuration in =net-misc/ntp-4.2.6_p5-r10 and added “noquery” to the default restriction which disallows anyone to query the ntpd status, including “monlist”.

If you use a non-default configuration, and provide a ntp service to untrusted networks, we highly recommend you to revise your configuration to disable mode 6 and 7 queries for any untrusted (public) network.

You can always enable these queries for specific trusted networks. For more details please see the “Access Control Support” chapter in the ntp.conf(5) man page.

Resolution

All NTP users should upgrade to the latest version:

 # emerge --sync
 # emerge --ask --oneshot --verbose ">=net-misc/ntp-4.2.6_p5-r10"

Note that the updated package contains a modified default configuration only. You may need to modify your configuration further.