NTP BUG 3454: Unauthenticated packet can reset authenticated interleaved association
Last update: April 22, 2024 18:49 UTC (7e7bd5857)
Summary
Description
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.
- 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.
Timeline