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CVE-2016-4953

33
FAUCET Score

CVE-2016-4953 describes a denial-of-service vulnerability in NTP 4.x before version 4.2.8p8, affecting products from vendors like openSUSE, Oracle, and Siemens. An unauthenticated remote attacker can exploit this flaw by sending a crafted crypto-NAK packet with incorrect authentication data, leading to ephemeral-association demobilization. This vulnerability carries a high CVSS score of 7.5, indicating a severe impact on availability with low attack complexity. While no public exploit code or active exploitation has been observed, the vulnerability has garnered some community discussion and media coverage, highlighting its potential risk.

Impacted Technologies

VendorProductVersion(s)CPE
>= 4.2.0, < 4.2.8CPE matchmatch criteria
cpe:2.3:a:ntp:ntp:*:*:*:*:*:*:*:*
>= 4.3.0, < 4.3.93CPE matchmatch criteria
cpe:2.3:a:ntp:ntp:*:*:*:*:*:*:*:*
4.2.8CPE matchmatch criteria
cpe:2.3:a:ntp:ntp:4.2.8:-:*:*:*:*:*:*
4.2.8CPE matchmatch criteria
cpe:2.3:a:ntp:ntp:4.2.8:p1:*:*:*:*:*:*
4.2.8CPE matchmatch criteria
cpe:2.3:a:ntp:ntp:4.2.8:p1-beta1:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

7.5HIGH

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

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
NONE
Integrity Impact
NONE
Availability Impact
HIGH
Exploitability Score
3.9
Impact Score
3.6
CvssVersion
3.1

Exploit Intelligence

EPSS Score
17.24%
Probability of exploitation in next 30 days
EPSS Percentile
96.8%
Percentile rank of EPSS score among Peer Group
As of 2026-07-25
Model: v2026.06.15
This CVE's current EPSS score of 0.1724 is in the 95th percentile among its peer group of 51,485 CVEs.

Social Chatter

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

Media Mentions

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Vendor Advisories (1)

redhatCVE-2016-4953Low

ntp: bad authentication demobilizes ephemeral associations

Jun 2, 2016

References

bugs.ntp.org / 3045
Issue TrackingVendor Advisory
lists.opensuse.org / opensuse-security-announce/2016-06/msg00018.html
Mailing ListThird Party Advisory
lists.opensuse.org / opensuse-security-announce/2016-06/msg00020.html
lists.opensuse.org / opensuse-security-announce/2016-06/msg00023.html
Mailing ListThird Party Advisory
lists.opensuse.org / opensuse-security-announce/2016-06/msg00024.html
Mailing ListThird Party Advisory
lists.opensuse.org / opensuse-security-announce/2016-06/msg00028.html
Mailing ListThird Party Advisory
lists.opensuse.org / opensuse-security-announce/2016-06/msg00040.html
Mailing ListThird Party Advisory
lists.opensuse.org / opensuse-security-announce/2016-07/msg00026.html
lists.opensuse.org / opensuse-security-announce/2016-08/msg00042.html
packetstormsecurity.com / files/137321/Slackware-Security-Advisory-ntp-Updates.html
packetstormsecurity.com / files/137322/FreeBSD-Security-Advisory-FreeBSD-SA-16-24.ntp.html
cert-portal.siemens.com / productcert/pdf/ssa-211752.pdf
Third Party Advisory
cert-portal.siemens.com / productcert/pdf/ssa-497656.pdf
Third Party Advisory
h20566.www2.hpe.com / hpsc/doc/public/display
Third Party Advisory
security.freebsd.org / advisories/FreeBSD-SA-16:24.ntp.asc
Third Party Advisory
security.gentoo.org / glsa/201607-15
Third Party Advisory
support.ntp.org / bin/view/Main/NtpBug3045
PatchVendor Advisory
support.ntp.org / bin/view/Main/SecurityNotice
Vendor Advisory
us-cert.cisa.gov / ics/advisories/icsa-21-103-11
Third Party AdvisoryUS Government Resource
us-cert.cisa.gov / ics/advisories/icsa-21-159-11
kb.cert.org / vuls/id/321640
tools.cisco.com / security/center/content/CiscoSecurityAdvisory/cisco-sa-20160603-ntpd
kb.cert.org / vuls/id/321640
Third Party AdvisoryUS Government Resource
oracle.com / technetwork/topics/security/bulletinapr2016-2952098.html
Third Party Advisory
securityfocus.com / archive/1/538599/100/0/threaded
securityfocus.com / archive/1/538600/100/0/threaded
securityfocus.com / archive/1/540683/100/0/threaded
securityfocus.com / archive/1/archive/1/538599/100/0/threaded
securityfocus.com / archive/1/archive/1/538600/100/0/threaded
securityfocus.com / archive/1/archive/1/540683/100/0/threaded
securityfocus.com / bid/91010
Third Party AdvisoryVDB Entry
securitytracker.com / id/1036037
Third Party AdvisoryVDB Entry