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CVE-2016-1547

21
FAUCET Score

CVE-2016-1547 describes a denial-of-service vulnerability affecting NTP 4.2.8p4 and earlier, as well as NTPSec a5fb34b9cc89b92a8fef2f459004865c93bb7f92. An unauthenticated, off-path attacker can disrupt a client's association with its NTP peer by sending a spoofed crypto NAK packet, even when authentication is enabled. This medium-severity vulnerability (CVSS 5.3) has a low impact of availability, requiring no user interaction. While there is no known active exploitation or public exploit code, the vulnerability has garnered significant community discussion and media coverage, indicating awareness within the cybersecurity community.

Impacted Technologies

VendorProductVersion(s)CPE
<= 4.2.8CPE matchmatch criteria
cpe:2.3:a:ntp:ntp:*:p4:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.0

5.3MEDIUM

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

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
NONE
Integrity Impact
NONE
Availability Impact
LOW
Exploitability Score
3.9
Impact Score
1.4
CvssVersion
3.0

Exploit Intelligence

EPSS Score
5.11%
Probability of exploitation in next 30 days
EPSS Percentile
91.5%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0511 is in the 88th percentile among its peer group of 23,701 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.0 Mastodon, and 0.4 GitHub mentions.

Media Mentions

The average CVE in this peer group has 0.0 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (4)

redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 6Fixed in: ntp-0:4.2.6p5-10.el6.1
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 6.7 Extended Update SupportFixed in: ntp-0:4.2.6p5-5.el6_7.5
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 7Fixed in: ntp-0:4.2.6p5-22.el7_2.2
View patch
redhatend of lifevia redhat_api
Product: Red Hat Enterprise Linux 5Fixed in: ntp

Vendor Advisories (1)

redhatCVE-2016-1547Moderate

ntp: crypto-NAK preemptable association denial of service

Apr 26, 2016

References

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