---
title: "CVE-2016-4956\n    | Ubuntu"
description: Ubuntu is an open source software operating system that runs from the
  desktop, to the cloud, to all your internet connected things.
url: https://ubuntu.com/security/CVE-2016-4956?format=md
keywords: index, follow
---

# CVE-2016-4956

Publication date 4 July 2016

Last updated 25 August 2025

---

Ubuntu priority

**Low**

[Why this priority?](https://ubuntu.com/security/cves/about#priority )

## Cvss 3 Severity Score

**5.3 · Medium**

[Score breakdown](https://ubuntu.com/security/CVE-2016-4956?format=md#impact-score)

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## Description

ntpd in NTP 4.x before 4.2.8p8 allows remote attackers to cause a denial of
service (interleaved-mode transition and time change) via a spoofed
broadcast packet. NOTE: this vulnerability exists because of an incomplete
fix for CVE-2016-1548.

[Read the notes from the security team](https://ubuntu.com/security/CVE-2016-4956?format=md#notes)

## Status

Show unmaintained releases

| Package | Ubuntu Release | Status |
| --- | --- | --- |
| ntp | 17.04 zesty | Not affected |
| 16.10 yakkety | Not affected |
| 16.04 LTS xenial | Fixed 1:4.2.8p4+dfsg-3ubuntu5.3 |
| 15.10 wily | Ignored end of life |
| 14.04 LTS trusty | Fixed 1:4.2.6.p5+dfsg-3ubuntu2.14.04.10 |
| 12.04 LTS precise | Fixed 1:4.2.6.p3+dfsg-1ubuntu3.11 |

---

* [How can I get the fixes?](https://ubuntu.com/security/cves/about#security)
* [What do statuses mean?](https://ubuntu.com/security/cves/about#statuses)
* [Patch details](https://ubuntu.com/security/CVE-2016-4956?format=md#patch-details)

## Notes

---

### [mdeslaur](https://launchpad.net/~mdeslaur)

incomplete fix for CVE-2016-1548

### Patch details

For informational purposes only. We recommend not to cherry-pick updates. [How can I get the fixes?](https://ubuntu.com/security/cves/about#security)

| Package | Patch details |
| --- | --- |
| ntp | * Vendor:   <http://pkgs.fedoraproject.org/cgit/rpms/ntp.git/tree/ntp-4.2.6p5-cve-2016-4956.patch> |

## Severity score breakdown

CVSS version:
CVSS v3.0

**Base score**

5.3 · Medium

* Base metrics

  | Parameter | Value |
  | --- | --- |
  | Attack vector | Network |
  | Attack complexity | Low |
  | Privileges required | None |
  | User interaction | None |
  | Scope | Unchanged |
  | Confidentiality impact | None |
  | Integrity impact | None |
  | Availability impact | Low |
* Scores

  | Parameter | Value |
  | --- | --- |
  | Base score | 5.3 · Medium |
  | Exploitability score | - |
  | Impact score | - |

**Vector:** CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

## References

* [MITRE](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-4956)
* [NVD](https://nvd.nist.gov/vuln/detail/CVE-2016-4956)
* [Launchpad](https://launchpad.net/bugs/cve/CVE-2016-4956)
* [Debian](https://security-tracker.debian.org/tracker/CVE-2016-4956)

### Related Ubuntu Security Notices (USN)

+ [USN-3096-1](https://usn.ubuntu.com/USN-3096-1)
+ NTP vulnerabilities
+ 5 October 2016

### Other references

* <http://support.ntp.org/bin/view/Main/SecurityNotice#June_2016_ntp_4_2_8p8_NTP_Securi>
* <https://www.cve.org/CVERecord?id=CVE-2016-4956>