# CVE-2016-1551: Security feature bypass in NTP

> Attackers can spoof reference clock packets to manipulate system time if OS-level martian packet filtering is disabled.

- **Severity:** Low 3.7 (`CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 27 Jan 2017
- **Updated:** 5 Aug 2024
- **Also known as:** GHSA-xhrh-m85j-g7hf

## What is CVE-2016-1551?

CVE-2016-1551 is a low-severity vulnerability in Ntp Ntp, published on 27 Jan 2017. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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.

Weakness: CWE-254

## Which versions are affected by CVE-2016-1551?

It affects 2 products.


Products: Ntp Ntp, Ntpsec Ntpsec.

## How do I fix CVE-2016-1551?

Apply the vendor's patch.

## Is CVE-2016-1551 being exploited?

There is no known exploitation of CVE-2016-1551 in the wild and no public exploit code.

## Other vulnerabilities in Ntp Ntp

- [CVE-2018-12327](https://insights.sbomify.com/CVE-2018-12327/): Memory corruption in n/a (critical 9.8)
- [CVE-2017-6460](https://insights.sbomify.com/CVE-2017-6460/): Memory corruption in n/a (high 8.8)
- [CVE-2019-11331](https://insights.sbomify.com/CVE-2019-11331/): Other in n/a (high 8.1)
- [CVE-2017-6451](https://insights.sbomify.com/CVE-2017-6451/): Memory corruption in n/a (high 7.8)
- [CVE-2017-6452](https://insights.sbomify.com/CVE-2017-6452/): Memory corruption in n/a (high 7.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2016-1551 and fix it if it is affected.

What it is: CVE-2016-1551 is a low-severity vulnerability in Ntp Ntp, published on 27 Jan 2017. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2016-1551 in the wild and no public exploit code.

Affected product: Ntp Ntp. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2016-1551/ (Markdown: https://insights.sbomify.com/CVE-2016-1551/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2016-1551
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2016-1551
- OSV: https://osv.dev/vulnerability/CVE-2016-1551

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From sbomify Insights: https://insights.sbomify.com/CVE-2016-1551/
Summaries are generated and may contain mistakes; the official description above is the record.