NTP users are strongly urged to take immediate action to ensure that their NTP daemons are not susceptible to being used in distributed denial-of-service (DDoS) attacks. Please also take this opportunity to defeat denial-of-service attacks by implementing Ingress and Egress filtering through BCP38.

ntp-4.2.8p13 was released on 07 March 2019. It addresses 1 medium-severity security issue in ntpd, and provides 17 non-security bugfixes and 1 other improvements over 4.2.8p12.

Please see the NTP Security Notice for vulnerability and mitigation details.

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NTP Bug 3113

Broadcast Mode Poll Interval Enforcement DoS

• Date Resolved: 21 Nov 2016
• References: Sec 3113 / CVE-2016-7428 / VU#633847
• Affects: ntp-4.2.8p6, up to but not including ntp-4.2.8p9, and ntp-4.3.90 up to, but not including ntp-4.3.94.
• CVSS2: LOW 3.3 (AV:A/AC:L/Au:N/C:N/I:N/A:P)
• CVSS3: MED 4.3 CVSS:3.0/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
• Summary: 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, from the NTP Project Download Page or the NTP Public Services Project Download Page
  • 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.