NTP BUG 3113: Broadcast Mode Poll Interval Enforcement DoS
Last update: April 22, 2024 18:49 UTC (7e7bd5857)
Summary
Description
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.
Mitigation
- Only use broadcast mode on trusted networks.
- Upgrade to 4.2.8p9 or later.
- Properly monitor your
ntpd
instances, and auto-restart ntpd
(without -g
) if it stops running.
Credit
This weakness was discovered by Matthew Van Gundy of Cisco.
Timeline