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Fencer Vulns
medium 5.3

CVE-2016-1547 json

An off-path attacker can cause a preemptible client association to be demobilized in NTP 4.2.8p4 and earlier and NTPSec a5fb34b9cc89b92a8fe…

published 2017-01-06 9 y ago modified 2026-06-17 4 mo ago also EUVD-2016-2642

cvss
5.3
version 3.0, NVD
cisa kev
Not listed
not in CISA's catalog
epss
5.1%
EPSS 5.1% chance of exploitation in 30 days, percentile 92%
public exploits
0
none known

Summary

An off-path attacker can cause a preemptible client association to be demobilized in NTP 4.2.8p4 and earlier and NTPSec a5fb34b9cc89b92a8fef2f459004865c93bb7f92 by sending a crypto NAK packet to a victim client with a spoofed source address of an existing associated peer. This is true even if authentication is enabled.

Patch / fix

  • ntp Debian 11 1:4.2.8p7+dfsg-1

debian advisories DEBIAN-CVE-2016-1547

  • 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-2016-1547

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 RHEL 6 4.2.6p5-10.el6.1
  • ntp RHEL 7 4.2.6p5-22.el7_2.2
  • sntp RHEL 7 4.2.6p5-22.el7_2.2
  • ntpdate RHEL 6 4.2.6p5-10.el6.1
  • ntpdate RHEL 7 4.2.6p5-22.el7_2.2
  • ntp-perl RHEL 6 4.2.6p5-10.el6.1
  • ntp-perl RHEL 7 4.2.6p5-22.el7_2.2
  • ntp RHEL 6.7 EUS 4.2.6p5-5.el6_7.5

red hat advisories RHSA-2016:1552RHSA-2016:1141

  • ntp SLES for SAP 12, SLES 12, SLED 12 4.2.8p8-46.8.1
  • ntp SLES 11 SP3-TERADATA, SLES 11 SP3-LTSS, SLES 11 SP2-LTSS +3 more 4.2.8p7-44.1
  • ntp SLES 12 SP1, SLES 11 SP4, SLED 12 SP1 +2 more 4.2.8p7-11.1

suse advisories SUSE-SU-2016:1568-1SUSE-SU-2016:1471-1SUSE-SU-2016:1291-1SUSE-SU-2016:1278-1

  • 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-2016-1547 updated cvss 4.3

ntp: crypto-NAK preemptable association denial of service

  • Red Hat Enterprise Linux 5 ntp
    affected: no fix planned “Will not fix”
  • Red Hat Enterprise Linux Client (v. 7) ntp 4.2.6p5-22.el7_2.2, ntpdate 4.2.6p5-22.el7_2.2 Red Hat Enterprise Linux Client Optional (v. 7) sntp 4.2.6p5-22.el7_2.2, ntp-perl 4.2.6p5-22.el7_2.2 Red Hat Enterprise Linux ComputeNode (v. 7) ntp 4.2.6p5-22.el7_2.2, ntpdate 4.2.6p5-22.el7_2.2 Red Hat Enterprise Linux ComputeNode Optional (v. 7) sntp 4.2.6p5-22.el7_2.2, ntp-perl 4.2.6p5-22.el7_2.2 Red Hat Enterprise Linux Desktop (v. 6) ntp 4.2.6p5-10.el6.1, ntpdate 4.2.6p5-10.el6.1 Red Hat Enterprise Linux Desktop Optional (v. 6) ntp-perl 4.2.6p5-10.el6.1
    +1 more products
    Red Hat Enterprise Linux HPC Node (v. 6) ntp 4.2.6p5-10.el6.1, ntpdate 4.2.6p5-10.el6.1
    fixed: vendor fix RHSA-2016:1141
  • Red Hat Enterprise Linux HPC Node EUS (v. 6.7) ntp 4.2.6p5-5.el6_7.5, ntpdate 4.2.6p5-5.el6_7.5
    fixed: vendor fix RHSA-2016:1552
  • Red Hat Enterprise Linux HPC Node Optional (v. 6) ntp-perl 4.2.6p5-10.el6.1
    fixed: vendor fix RHSA-2016:1141
  • Red Hat Enterprise Linux HPC Node Optional EUS (v. 6.7) ntp-perl 4.2.6p5-5.el6_7.5
    fixed: vendor fix RHSA-2016:1552
  • Red Hat Enterprise Linux Server (v. 6) ntp 4.2.6p5-10.el6.1, ntpdate 4.2.6p5-10.el6.1 Red Hat Enterprise Linux Server (v. 7) ntp 4.2.6p5-22.el7_2.2, ntpdate 4.2.6p5-22.el7_2.2
    fixed: vendor fix RHSA-2016:1141
  • Red Hat Enterprise Linux Server EUS (v. 6.7) ntp 4.2.6p5-5.el6_7.5, ntpdate 4.2.6p5-5.el6_7.5
    fixed: vendor fix RHSA-2016:1552
  • Red Hat Enterprise Linux Server Optional (v. 6) ntp-perl 4.2.6p5-10.el6.1 Red Hat Enterprise Linux Server Optional (v. 7) sntp 4.2.6p5-22.el7_2.2, ntp-perl 4.2.6p5-22.el7_2.2
    fixed: vendor fix RHSA-2016:1141
show 2 more
  • Red Hat Enterprise Linux Server Optional EUS (v. 6.7) ntp-perl 4.2.6p5-5.el6_7.5
    fixed: vendor fix RHSA-2016:1552
  • Red Hat Enterprise Linux Workstation (v. 6) ntp 4.2.6p5-10.el6.1, ntpdate 4.2.6p5-10.el6.1 Red Hat Enterprise Linux Workstation (v. 7) ntp 4.2.6p5-22.el7_2.2, ntpdate 4.2.6p5-22.el7_2.2 Red Hat Enterprise Linux Workstation Optional (v. 6) ntp-perl 4.2.6p5-10.el6.1 Red Hat Enterprise Linux Workstation Optional (v. 7) sntp 4.2.6p5-22.el7_2.2, ntp-perl 4.2.6p5-22.el7_2.2
    fixed: vendor fix RHSA-2016:1141

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-21-103-11 updated cvss 5.3

Siemens TIM 4R-IE Devices

  • Siemens SIPLUS NET TIM 4R-IE (6AG1800-4BA00-7AA0) Siemens SIPLUS NET TIM 4R-IE DNP3 (6AG1803-4BA00-7AA0) Siemens TIM 4R-IE (6NH7800-4BA00) Siemens TIM 4R-IE DNP3 (6NH7803-4BA00-0AA0)
    affected: workaround, 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

cisa ICSA-21-159-11 updated cvss 5.3

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

5.07% chance of exploitation in the next 30 days, higher than 92% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.0 5.3 CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
NVD 2.0 5.0 AV:N/AC:L/Au:N/C:N/I:N/A:P

Affected products

  • NTP Project NTP
  • NTPsec Project NTPSec

Classification

Weakness
  • CWE-20 Improper Input Validation

References

Sources

Fencer Vulns 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.