CVE-2016-1551

What it is

ntpd in NTP 4.2.8p3 and NTPsec a5fb34b9cc89b92a8fef2f459004865c93bb7f92 relies on the underlying operating system to protect it from requests that impersonate reference clocks. Because reference clocks are treated like other peers and stored in the same structure, any packet with a source ip address of a reference clock (127.127.1.1 for example) that reaches the receive() function will match that reference clock's peer record and will be treated as a trusted peer. Any system that lacks the typical martian packet filtering which would block these packets is in danger of having its time controlled by an attacker.

At a glance

Exploitability

Can be exploited over the network without logging in. Limited direct impact.

Exploit odds

2.2% chance of exploitation in the next 30 days (EPSS).

Fix

No patch or advisory is linked yet. Look at mitigations or restrict exposure.

Timeline

1. 2017-01-27 17:59 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 00:42 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 2.2% in the next 30 days (EPSS).
• Severity: 3.7 LOW (CVSS).
• Fix: none linked yet, which raises it.

Details

Published

2017-01-27 17:59 UTC

Last modified

2026-06-17 00:42 UTC

Exploit probability

2.2% · EPSS, next 30 days

Weakness

CWE-254

Record status

Modified

Affected

• Ntp 4.2.8
• Ntpsec a5fb34b9cc89b92a8fef2f459004865c93bb7f92

Attack profile CVSS 3.0 · 3.7

Attack vector

Network

Complexity

High

Privileges needed

None

User interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

Low

Availability

None

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2016-1551.md and follow it. Check whether this project is affected by CVE-2016-1551. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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