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CVE-2016-4956

27
FAUCET Score

CVE-2016-4956 is a denial-of-service vulnerability affecting NTP 4.x before version 4.2.8p8, specifically impacting products from Novell, openSUSE, Oracle, Siemens, and SUSE. This medium-severity flaw (CVSS 5.3) allows an unauthenticated remote attacker to disrupt time synchronization via a spoofed broadcast packet, leading to an interleaved-mode transition and time change. While no public exploit code or Metasploit modules are available, the vulnerability has received some community discussion and media coverage, indicating awareness. There is no evidence of active exploitation, and it is not listed on the CISA KEV catalog.

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

5.3MEDIUM

CVSS:3.1/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
3.1

Exploit Intelligence

EPSS Score
16.35%
Probability of exploitation in next 30 days
EPSS Percentile
96.6%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.1635 is in the 96th percentile among its peer group of 23,703 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

Vendor Patches (3)

redhatend of lifevia redhat_api
Product: Red Hat Enterprise Linux 5Fixed in: ntp
redhatend of lifevia redhat_api
Product: Red Hat Enterprise Linux 6Fixed in: ntp
redhatend of lifevia redhat_api
Product: Red Hat Enterprise Linux 7Fixed in: ntp

Vendor Advisories (1)

redhatCVE-2016-4956Low

ntp: broadcast interleave (incomplete fix for CVE-2016-1548)

Jun 2, 2016

References

bugs.ntp.org / 3042
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
cert-portal.siemens.com / productcert/pdf/ssa-211752.pdf
Third Party Advisory
h20566.www2.hpe.com / hpsc/doc/public/display
Third Party Advisory
lists.fedoraproject.org / archives/list/package-announce%40lists.fedoraproject.org/message/K3EYJQHJZ2KTVQ7ICEFHXTLZ36MRASWX
lists.fedoraproject.org / archives/list/package-announce%40lists.fedoraproject.org/message/ORAMN3Q7TVJ54MBYF75XCJOE3DP7LYHT
lists.fedoraproject.org / archives/list/package-announce%40lists.fedoraproject.org/message/WNWGCQLW2VY72NIUYMJOCAKJKTXHDUK2
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/NtpBug3042
Vendor Advisory
support.ntp.org / bin/view/Main/SecurityNotice
Release NotesVendor Advisory
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/91009
Third Party AdvisoryVDB Entry
securitytracker.com / id/1036037
Third Party AdvisoryVDB Entry
ubuntu.com / usn/USN-3096-1