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Vulnerability record · CVE-2016-1547 · published 6 January 2017

CVE-2016-1547: Ntp improper input validation vulnerability

Ntp · Ntp

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.

5.3 CVSS 3.0 Medium EPSS 5.1% · top 7.9% CWE-20 · Improper input validation
5.3CVSS 3.0 base score, v2 5.0
5.1%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
30References
17 Jun 2026Last modified by NVD

Description

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.

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
http://rhn.redhat.com/errata/RHSA-2016-1552.html
http://www.debian.org/security/2016/dsa-3629
http://www.oracle.com/technetwork/topics/security/bulletinapr2016-2952098.html
http://www.oracle.com/technetwork/topics/security/linuxbulletinapr2016-2952096.html
http://www.securityfocus.com/bid/88276
http://www.securitytracker.com/id/1035705
http://www.talosintelligence.com/reports/TALOS-2016-0081/ MitigationTechnical DescriptionThird Party Advisory
https://access.redhat.com/errata/RHSA-2016:1141
https://cert-portal.siemens.com/productcert/pdf/ssa-211752.pdf
https://cert-portal.siemens.com/productcert/pdf/ssa-497656.pdf
https://security.FreeBSD.org/advisories/FreeBSD-SA-16:16.ntp.asc
https://security.gentoo.org/glsa/201607-15
https://security.netapp.com/advisory/ntap-20171004-0002/
https://us-cert.cisa.gov/ics/advisories/icsa-21-103-11
https://www.arista.com/en/support/advisories-notices/security-advisories/1332-security-advisory-19
http://rhn.redhat.com/errata/RHSA-2016-1552.html
http://www.debian.org/security/2016/dsa-3629
http://www.oracle.com/technetwork/topics/security/bulletinapr2016-2952098.html
http://www.oracle.com/technetwork/topics/security/linuxbulletinapr2016-2952096.html
http://www.securityfocus.com/bid/88276
http://www.securitytracker.com/id/1035705
http://www.talosintelligence.com/reports/TALOS-2016-0081/ MitigationTechnical DescriptionThird Party Advisory
https://access.redhat.com/errata/RHSA-2016:1141
https://cert-portal.siemens.com/productcert/pdf/ssa-211752.pdf
https://cert-portal.siemens.com/productcert/pdf/ssa-497656.pdf
https://security.FreeBSD.org/advisories/FreeBSD-SA-16:16.ntp.asc
https://security.gentoo.org/glsa/201607-15
https://security.netapp.com/advisory/ntap-20171004-0002/
https://us-cert.cisa.gov/ics/advisories/icsa-21-103-11
https://www.arista.com/en/support/advisories-notices/security-advisories/1332-security-advisory-19

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

9.8CVE-2018-12327Ntp out-of-bounds write vulnerabilityStack-based buffer overflow in ntpq and ntpdc of NTP version 4.2.8p11 allows an attacker to achieve code execution or escalate to higher privileges v…EPSS 28%9.8CVE-2018-7183Ntp out-of-bounds write vulnerabilityBuffer overflow in the decodearr function in ntpq in ntp 4.2.8p6 through 4.2.8p10 allows remote attackers to execute arbitrary code by leveraging an …EPSS 10%9.8CVE-2015-7705Ntp improper input validation vulnerabilityThe rate limiting feature in NTP 4.x before 4.2.8p4 and 4.3.x before 4.3.77 allows remote attackers to have unspecified impact via a large number of …EPSS 12%9.8CVE-2015-7853Ntp classic buffer overflow vulnerabilityThe datalen parameter in the refclock driver in NTP 4.2.x before 4.2.8p4, and 4.3.x before 4.3.77 allows remote attackers to execute arbitrary code o…EPSS 12%9.8CVE-2015-7871ntpd Crypto-NAK packets bypass authenticationntpd in NTP 4.2.x before 4.2.8p4 and 4.3.x before 4.3.77 mishandles Crypto-NAK packets, allowing remote attackers to bypass authentication. Because N…EPSS 82%analysed8.8CVE-2015-7849Ntp use after free vulnerabilityUse-after-free vulnerability in ntpd in NTP 4.2.x before 4.2.8p4, and 4.3.x before 4.3.77 allows remote authenticated users to possibly execute arbit…EPSS 17%8.8CVE-2015-7854Ntp classic buffer overflow vulnerabilityBuffer overflow in the password management functionality in NTP 4.2.x before 4.2.8p4, and 4.3.x before 4.3.77 allows remote authenticated users to ca…EPSS 15%8.8CVE-2017-6458Ntp memory buffer overflow vulnerabilityMultiple buffer overflows in the ctl_put* functions in NTP before 4.2.8p10 and 4.3.x before 4.3.94 allow remote authenticated users to have unspecifi…EPSS 6.5%

Source: NIST National Vulnerability Database (record CVE-2016-1547), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.