CVE-2016-4955

ntpd in NTP 4.x before 4.2.8p8, when autokey is enabled, allows remote attackers to cause a denial of service (peer-variable clearing and association outage) by sending (1) a spoofed crypto-NAK packet or (2) a packet with an incorrect MAC value at a certain time.

Published: 2016-07-04 Last update: 2026-06-16 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2016-4955 is rated Moderate Risk (61.7/100): CVSS Medium severity, with high exploitation likelihood (EPSS 8.80%, 94th percentile). EPSS ranks this CVE among the most likely to be exploited in the near term. EPSS rose +7.08% over the last day, indicating growing attacker interest. 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-2016-4955

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 2026-06-15 1.73% 8.80% +7.08%
2 2026-05-03 1.90% 1.73% -0.18%
3 2026-02-23 — 1.90% —

Full EPSS history (22 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2016-4955

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.9 3.1 MEDIUM
CVSS:3.1/AV:N/AC:H/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:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
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.
 2.2 3.6 [email protected]
4.3 2.0 MEDIUM
AV:N/AC:M/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:M)
Exploitation needs some favorable conditions, but not exceptional ones.
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.
 8.6 2.9 [email protected]

Weakness enumeration for CVE-2016-4955

OS Trackers for CVE-2016-4955

vendor priority summary link
debian not yet assigned CVE-2016-4955 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-2016-4955
gentoo normal CVE-2016-4955: 1 GLSA(s) (201607-15), 1 atom(s) (net-misc/ntp); latest impact normal. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2016-4955
redhat low — https://access.redhat.com/security/cve/CVE-2016-4955
suse low CVE-2016-4955 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-2016-4955/
ubuntu low CVE-2016-4955 low priority: Ubuntu including 1 source packages (ntp), 7 status rows across 7 suites (precise, trusty, upstream, wily, xenial, yakkety, zesty): released 3, not-affected 2, ignored 1, needs-triage 1. https://ubuntu.com/security/CVE-2016-4955

Affected software / configurations for CVE-2016-4955

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_proxy 2.1 cpe:2.3:a:suse:manager_proxy:2.1:*:*:*:*:*:*:*
suse openstack_cloud 5 cpe:2.3:a:suse:openstack_cloud:5:*:*:*:*:*:*:*
novell suse_manager 2.1 cpe:2.3:o:novell:suse_manager:2.1:*:*:*:*:*:*:*
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:*:*:*:*:*:*:*:*

References for CVE-2016-4955

URL Tags
http://bugs.ntp.org/3043 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/NtpBug3043 Patch Vendor Advisory
http://support.ntp.org/bin/view/Main/SecurityNotice Release Notes 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/archive/1/538599/100/0/threaded
http://www.securityfocus.com/archive/1/archive/1/538600/100/0/threaded
http://www.securityfocus.com/bid/91007 Third Party Advisory VDB Entry
http://www.securitytracker.com/id/1036037 Third Party Advisory VDB Entry
http://www.ubuntu.com/usn/USN-3096-1
https://cert-portal.siemens.com/productcert/pdf/ssa-211752.pdf Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/K3EYJQHJZ2KTVQ7ICEFHXTLZ36MRASWX/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ORAMN3Q7TVJ54MBYF75XCJOE3DP7LYHT/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/WNWGCQLW2VY72NIUYMJOCAKJKTXHDUK2/
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-21-159-11
https://www.kb.cert.org/vuls/id/321640
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