# CVE-2016-4953: Denial of service in n/a

> Remote attackers can cause a denial of service in NTP by sending spoofed crypto-NAK packets with incorrect authentication data.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 5 Jul 2016
- **Updated:** 6 Aug 2024
- **Also known as:** DEBIAN-CVE-2016-4953, GHSA-26jw-7mv6-89rj

## What is CVE-2016-4953?

CVE-2016-4953 is a high-severity denial of service vulnerability in Ntp Ntp, published on 5 Jul 2016. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

ntpd in NTP 4.x before 4.2.8p8 allows remote attackers to cause a denial of service (ephemeral-association demobilization) by sending a spoofed crypto-NAK packet with incorrect authentication data at a certain time.

Weakness: CWE-287 (Improper Authentication)

## Which versions are affected by CVE-2016-4953?

It affects 12 products.


Products: Ntp Ntp, Opensuse Leap, Opensuse Opensuse, Oracle Solaris, Siemens Simatic Net Cp 443-1 Opc Ua Firmware, Siemens Tim 4r-Ie Dnp3 Firmware, Siemens Tim 4r-Ie Firmware, Suse Linux Enterprise Desktop, Suse Linux Enterprise Server, Suse Manager, Suse Manager Proxy, Suse Openstack Cloud.

## How do I fix CVE-2016-4953?

Upgrade to a fixed version.

## Is CVE-2016-4953 being exploited?

There is no known exploitation of CVE-2016-4953 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-2016-4953 and fix it if it is affected.

What it is: CVE-2016-4953 is a high-severity denial of service vulnerability in Ntp Ntp, published on 5 Jul 2016. 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-2016-4953 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-2016-4953/ (Markdown: https://insights.sbomify.com/CVE-2016-4953/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2016-4953
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2016-4953
- OSV: https://osv.dev/vulnerability/CVE-2016-4953

---
From sbomify Insights: https://insights.sbomify.com/CVE-2016-4953/
Summaries are generated and may contain mistakes; the official description above is the record.