NTP BUG 3113: Broadcast Mode Poll Interval Enforcement DoS
Last update: February 15, 2022 20:59 UTC (43fbd379b)
The broadcast mode of NTP is expected to only be used in a trusted network. If the broadcast network is accessible to an attacker, a potentially exploitable denial of service vulnerability in
ntpd’s broadcast mode poll interval enforcement functionality can be abused. To limit abuse,
ntpd restricts the rate at which each broadcast association will process incoming packets.
ntpd will reject broadcast mode packets that arrive before the poll interval specified in the preceding broadcast packet expires. An attacker with access to the NTP broadcast domain can send specially crafted broadcast mode NTP packets to the broadcast domain which, while being logged by
ntpd, will cause
ntpd to reject broadcast mode packets from legitimate NTP broadcast servers.
- Only use broadcast mode on trusted networks.
- Upgrade to 4.2.8p9 or later.
- Properly monitor your
ntpd instances, and auto-restart
-g) if it stops running.
This weakness was discovered by Matthew Van Gundy of Cisco.