NTP BUG 3110: Windows: ntpd DoS by oversized UDP packet

Last update: September 3, 2026 14:42 UTC (1eec487e7)

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Summary

Resolved	4.2.8p9	21 Nov 2016
References	Bug 3110	CVE-2016-9312
Affects	Windows only: ntp-4.?.?, up to but not including ntp-4.2.8p9, and ntp-4.3.0 up to, but not including ntp-4.3.94.	Resolved in 4.2.8p9.
CVSS2 Score	HIGH 7.8	AV:N/AC:L/Au:N/C:N/I:N/A:C
CVSS3 Score	HIGH 7.5	CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

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Description

If a vulnerable instance of ntpd on Windows receives a crafted malicious packet that is “too big”, ntpd will stop working.

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Mitigation

• Implement BCP-38.
• Implement a firewall rule blocking oversized NTP packets.
• Upgrade to 4.2.8p9 or later.
• Properly monitor your ntpd instances, and auto-restart ntpd (without -g) if it stops running.

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Credit

This weakness was discovered by Robert Pajak of ABB.

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Timeline

• 2016 Nov 21: Public release
• 2016 Nov 15: CERT given our software release notification
• 2016 Nov 14: Early Access Program Release: Premier and Partner Institutional Members
• : Notification to Institutional Members
• : Report received