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Fencer Intel
medium 5.9

CVE-2016-4955 json

ntpd in NTP 4.x before 4.2.8p8, when autokey is enabled, allows remote attackers to cause a denial of service (peer-variable clearing and a…

published 2016-07-05 10 y ago modified 2026-06-17 4 mo ago also EUVD-2016-5929

cvss
5.9
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
8.8%
EPSS 8.8% chance of exploitation in 30 days, percentile 95%
public exploits
0
none known

Summary

ntpd in NTP 4.x before 4.2.8p8, when autokey is enabled, allows remote attackers to cause a denial of service (peer-variable clearing and association outage) by sending (1) a spoofed crypto-NAK packet or (2) a packet with an incorrect MAC value at a certain time.

Patch / fix

  • ntp ntp 4.2.8, 4.3.93
  • ntp Debian 11 1:4.2.8p8+dfsg-1

debian advisories DEBIAN-CVE-2016-4955

  • ntp Ubuntu 14.04 LTS 1:4.2.6.p5+dfsg-3ubuntu2.14.04.10
  • ntp Ubuntu 16.04 LTS 1:4.2.8p4+dfsg-3ubuntu5.3

ubuntu advisories UBUNTU-CVE-2016-4955

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • ntp SLES 11 SP3-TERADATA, SLES 11 SP3-LTSS, SLES 11 SP2-LTSS +3 more 4.2.8p8-47.3
  • ntp SLES 12 SP1, SLES 11 SP4, SLED 12 SP1 +2 more 4.2.8p8-14.1
  • ntp SLES for SAP 12, SLES 12, SLED 12 4.2.8p8-46.8.1

suse advisories SUSE-SU-2016:1602-1SUSE-SU-2016:1584-1SUSE-SU-2016:1568-1SUSE-SU-2016:1563-1

  • ntp openSUSE Tumbleweed 4.2.8p9-1.1

opensuse advisories openSUSE-SU-2024:10181-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2016-4955 updated cvss 2.6

ntp: autokey association reset

  • Red Hat Enterprise Linux 5 ntp Red Hat Enterprise Linux 6 ntp, ntpdate, ntp-perl Red Hat Enterprise Linux 7 ntp, sntp, ntpdate, ntp-perl
    affected: workaround, no fix planned “Will not fix”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

cisa ICSA-21-159-11 updated cvss 5.9

Siemens SIMATIC NET CP 443-1 OPC UA

  • Siemens SIMATIC CP 443-1 OPC UA
    affected: mitigation, no fix planned

Facts from CISA's republication of the vendor's own advisory (CSAF); the linked advisory is the authoritative source. CISA notification · csaf

Exploit prediction

8.77% chance of exploitation in the next 30 days, higher than 95% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
NVD 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD 2.0 4.3 AV:N/AC:M/Au:N/C:N/I:N/A:P

Classification

Weakness
  • CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.