CVE-2016-4953

ntpd in NTP 4.x before 4.2.8p8 allows remote attackers to cause a denial of service (ephemeral-association demobilization) by sending a spoofed crypto-NAK packet with incorrect authentication data at a certain time.

Published: 2016-07-05 Last update: 2026-05-06 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2016-4953 is rated Moderate Risk (62/100): CVSS High severity, with high exploitation likelihood (EPSS 12.72%, 94th percentile). EPSS ranks this CVE among the most likely to be exploited in the near term. High exploitation likelihood—assess exposure and prioritize remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2016-4953

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-03 13.62% 12.72% -0.90%
2 2026-05-03 14.37% 13.62% -0.75%
3 2025-12-28 — 14.37% —

Full EPSS history (25 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2016-4953

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 3.6 [email protected]
5.0 2.0 MEDIUM
AV:N/AC:L/Au:N/C:N/I:N/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:P)
Partial availability impact.
 10.0 2.9 [email protected]

Weakness enumeration for CVE-2016-4953

OS Trackers for CVE-2016-4953

vendor priority summary link
debian not yet assigned CVE-2016-4953 not yet assigned priority: Debian including 1 source packages (ntp), 1 status rows across 1 suites (bullseye): resolved 1. https://security-tracker.debian.org/tracker/CVE-2016-4953
gentoo normal CVE-2016-4953: 1 GLSA(s) (201607-15), 1 atom(s) (net-misc/ntp); latest impact normal. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2016-4953
redhat low — https://access.redhat.com/security/cve/CVE-2016-4953
suse low CVE-2016-4953 severity low: SUSE including 20 source package names (ntp-4.2.8p10-63.3, ntp-4.2.8p11-2.12, …), 80 product×package rows across 54 product lines (Image SLES12-SP5-Azure-BYOS, Image SLES12-SP5-Azure-Basic-On-Demand, … (54 product lines)): Fixed 80. https://www.suse.com/security/cve/CVE-2016-4953/
ubuntu medium CVE-2016-4953 medium priority: Ubuntu including 1 source packages (ntp), 5 status rows across 5 suites (precise, trusty, upstream, wily, xenial): not-affected 3, ignored 1, needs-triage 1. https://ubuntu.com/security/CVE-2016-4953

Affected software / configurations for CVE-2016-4953

Vendor Product Version Raw CPE
ntp ntp >= 4.2.0, < 4.2.8 cpe:2.3:a:ntp:ntp:*:*:*:*:*:*:*:*
ntp ntp >= 4.3.0, < 4.3.93 cpe:2.3:a:ntp:ntp:*:*:*:*:*:*:*:*
ntp ntp 4.2.8 cpe:2.3:a:ntp:ntp:4.2.8:-:*:*:*:*:*:*
ntp ntp 4.2.8 cpe:2.3:a:ntp:ntp:4.2.8:p1:*:*:*:*:*:*
ntp ntp 4.2.8 cpe:2.3:a:ntp:ntp:4.2.8:p1-beta1:*:*:*:*:*:*
ntp ntp 4.2.8 cpe:2.3:a:ntp:ntp:4.2.8:p1-beta2:*:*:*:*:*:*
ntp ntp 4.2.8 cpe:2.3:a:ntp:ntp:4.2.8:p1-beta3:*:*:*:*:*:*
ntp ntp 4.2.8 cpe:2.3:a:ntp:ntp:4.2.8:p1-beta4:*:*:*:*:*:*
ntp ntp 4.2.8 cpe:2.3:a:ntp:ntp:4.2.8:p1-beta5:*:*:*:*:*:*
ntp ntp 4.2.8 cpe:2.3:a:ntp:ntp:4.2.8:p1-rc1:*:*:*:*:*:*
ntp ntp 4.2.8 cpe:2.3:a:ntp:ntp:4.2.8:p1-rc2:*:*:*:*:*:*
ntp ntp 4.2.8 cpe:2.3:a:ntp:ntp:4.2.8:p2:*:*:*:*:*:*
ntp ntp 4.2.8 cpe:2.3:a:ntp:ntp:4.2.8:p2-rc1:*:*:*:*:*:*
ntp ntp 4.2.8 cpe:2.3:a:ntp:ntp:4.2.8:p2-rc2:*:*:*:*:*:*
ntp ntp 4.2.8 cpe:2.3:a:ntp:ntp:4.2.8:p2-rc3:*:*:*:*:*:*
ntp ntp 4.2.8 cpe:2.3:a:ntp:ntp:4.2.8:p3:*:*:*:*:*:*
ntp ntp 4.2.8 cpe:2.3:a:ntp:ntp:4.2.8:p3-rc1:*:*:*:*:*:*
ntp ntp 4.2.8 cpe:2.3:a:ntp:ntp:4.2.8:p3-rc2:*:*:*:*:*:*
ntp ntp 4.2.8 cpe:2.3:a:ntp:ntp:4.2.8:p3-rc3:*:*:*:*:*:*
ntp ntp 4.2.8 cpe:2.3:a:ntp:ntp:4.2.8:p4:*:*:*:*:*:*
ntp ntp 4.2.8 cpe:2.3:a:ntp:ntp:4.2.8:p5:*:*:*:*:*:*
ntp ntp 4.2.8 cpe:2.3:a:ntp:ntp:4.2.8:p6:*:*:*:*:*:*
ntp ntp 4.2.8 cpe:2.3:a:ntp:ntp:4.2.8:p7:*:*:*:*:*:*
oracle solaris 10 cpe:2.3:o:oracle:solaris:10:*:*:*:*:*:*:*
oracle solaris 11.3 cpe:2.3:o:oracle:solaris:11.3:*:*:*:*:*:*:*
suse manager 2.1 cpe:2.3:a:suse:manager:2.1:*:*:*:*:*:*:*
suse manager_proxy 2.1 cpe:2.3:a:suse:manager_proxy:2.1:*:*:*:*:*:*:*
suse openstack_cloud 5 cpe:2.3:a:suse:openstack_cloud:5:*:*:*:*:*:*:*
opensuse leap 42.1 cpe:2.3:o:opensuse:leap:42.1:*:*:*:*:*:*:*
opensuse opensuse 13.2 cpe:2.3:o:opensuse:opensuse:13.2:*:*:*:*:*:*:*
suse linux_enterprise_desktop 12 cpe:2.3:o:suse:linux_enterprise_desktop:12:sp1:*:*:*:*:*:*
suse linux_enterprise_server 11 cpe:2.3:o:suse:linux_enterprise_server:11:sp2:*:*:ltss:*:*:*
suse linux_enterprise_server 11 cpe:2.3:o:suse:linux_enterprise_server:11:sp3:*:*:ltss:*:*:*
suse linux_enterprise_server 11 cpe:2.3:o:suse:linux_enterprise_server:11:sp4:*:*:*:*:*:*
suse linux_enterprise_server 12 cpe:2.3:o:suse:linux_enterprise_server:12:sp1:*:*:*:*:*:*
siemens simatic_net_cp_443-1_opc_ua_firmware — cpe:2.3:o:siemens:simatic_net_cp_443-1_opc_ua_firmware:*:*:*:*:*:*:*:*
siemens tim_4r-ie_firmware — cpe:2.3:o:siemens:tim_4r-ie_firmware:*:*:*:*:*:*:*:*
siemens tim_4r-ie_dnp3_firmware — cpe:2.3:o:siemens:tim_4r-ie_dnp3_firmware:*:*:*:*:*:*:*:*

References for CVE-2016-4953

URL Tags
http://bugs.ntp.org/3045 Issue Tracking Vendor Advisory
http://lists.opensuse.org/opensuse-security-announce/2016-06/msg00018.html Mailing List Third Party Advisory
http://lists.opensuse.org/opensuse-security-announce/2016-06/msg00020.html
http://lists.opensuse.org/opensuse-security-announce/2016-06/msg00023.html Mailing List Third Party Advisory
http://lists.opensuse.org/opensuse-security-announce/2016-06/msg00024.html Mailing List Third Party Advisory
http://lists.opensuse.org/opensuse-security-announce/2016-06/msg00028.html Mailing List Third Party Advisory
http://lists.opensuse.org/opensuse-security-announce/2016-06/msg00040.html Mailing List Third Party Advisory
http://lists.opensuse.org/opensuse-security-announce/2016-07/msg00026.html
http://lists.opensuse.org/opensuse-security-announce/2016-08/msg00042.html
http://packetstormsecurity.com/files/137321/Slackware-Security-Advisory-ntp-Updates.html
http://packetstormsecurity.com/files/137322/FreeBSD-Security-Advisory-FreeBSD-SA-16-24.ntp.html
http://support.ntp.org/bin/view/Main/NtpBug3045 Patch Vendor Advisory
http://support.ntp.org/bin/view/Main/SecurityNotice Vendor Advisory
http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20160603-ntpd
http://www.kb.cert.org/vuls/id/321640 Third Party Advisory US Government Resource
http://www.oracle.com/technetwork/topics/security/bulletinapr2016-2952098.html Third Party Advisory
http://www.securityfocus.com/archive/1/538599/100/0/threaded
http://www.securityfocus.com/archive/1/538600/100/0/threaded
http://www.securityfocus.com/archive/1/540683/100/0/threaded
http://www.securityfocus.com/archive/1/archive/1/538599/100/0/threaded
http://www.securityfocus.com/archive/1/archive/1/538600/100/0/threaded
http://www.securityfocus.com/archive/1/archive/1/540683/100/0/threaded
http://www.securityfocus.com/bid/91010 Third Party Advisory VDB Entry
http://www.securitytracker.com/id/1036037 Third Party Advisory VDB Entry
https://cert-portal.siemens.com/productcert/pdf/ssa-211752.pdf Third Party Advisory
https://cert-portal.siemens.com/productcert/pdf/ssa-497656.pdf Third Party Advisory
https://h20566.www2.hpe.com/hpsc/doc/public/display?docLocale=en_US&docId=emr_na-hpesbhf03757en_us Third Party Advisory
https://security.FreeBSD.org/advisories/FreeBSD-SA-16:24.ntp.asc Third Party Advisory
https://security.gentoo.org/glsa/201607-15 Third Party Advisory
https://us-cert.cisa.gov/ics/advisories/icsa-21-103-11 Third Party Advisory US Government Resource
https://us-cert.cisa.gov/ics/advisories/icsa-21-159-11
https://www.kb.cert.org/vuls/id/321640
cvelogic Threat Intelligence