NTP BUG 3453: Interleaved symmetric mode cannot recover from bad state
Last update: February 15, 2022 15:25 UTC (b158e7036)
The fix for NTP Bug 2952 was incomplete, and while it fixed one problem it created another. Specifically, it drops bad packets before updating the “received” timestamp. This means a third-party can inject a packet with a zero-origin timestamp, meaning the sender wants to reset the association, and the transmit timestamp in this bogus packet will be saved as the most recent “received” timestamp. The real remote peer does not know this value and this will disrupt the association until the association resets.
- Implement BCP-38.
- Upgrade to 4.2.8p11 or later.
- Use authentication with peer mode.
- Have enough sources of time.
- Properly monitor your
ntpd stops running, auto-restart it without
This weakness was discovered by Miroslav Lichvar of Red Hat.