CVE-2016-4953

CVE-2016-4953 is a high-severity vulnerability in Ntp with a CVSS 3.x base score of 7.5. Its EPSS exploit-prediction score of 17% places it in the 97th percentile, indicating an elevated likelihood of exploitation. The underlying weakness is classified as CWE-287.

Key facts

• Severity: High (CVSS 3.x base score 7.5)
• CVSS v2: 5.0
• EPSS exploit prediction: 17% (97th percentile)
• Actively exploited: Not listed in CISA KEV
• Weakness: CWE-287
• Affected product: Ntp
• Published: 2016-07-05
• Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is 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.

How severe is CVE-2016-4953?

CVE-2016-4953 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2016-4953 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 17% (97th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2016-4953?

CVE-2016-4953 primarily affects Ntp. In total, 37 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2016-4953?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2016-4953 published?

CVE-2016-4953 was published on 2016-07-05 and last updated on 2026-06-17.

References

• http://bugs.ntp.org/3045
• http://lists.opensuse.org/opensuse-security-announce/2016-06/msg00018.html
• http://lists.opensuse.org/opensuse-security-announce/2016-06/msg00020.html
• http://lists.opensuse.org/opensuse-security-announce/2016-06/msg00023.html
• http://lists.opensuse.org/opensuse-security-announce/2016-06/msg00024.html
• http://lists.opensuse.org/opensuse-security-announce/2016-06/msg00028.html
• http://lists.opensuse.org/opensuse-security-announce/2016-06/msg00040.html
• 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
• http://support.ntp.org/bin/view/Main/SecurityNotice
• http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20160603-ntpd
• http://www.kb.cert.org/vuls/id/321640
• http://www.oracle.com/technetwork/topics/security/bulletinapr2016-2952098.html
• 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
• http://www.securitytracker.com/id/1036037
• https://cert-portal.siemens.com/productcert/pdf/ssa-211752.pdf
• https://cert-portal.siemens.com/productcert/pdf/ssa-497656.pdf
• https://h20566.www2.hpe.com/hpsc/doc/public/display?docLocale=en_US&docId=emr_na-hpesbhf03757en_us
• https://security.FreeBSD.org/advisories/FreeBSD-SA-16:24.ntp.asc
• https://security.gentoo.org/glsa/201607-15
• https://us-cert.cisa.gov/ics/advisories/icsa-21-103-11

Affected products (37)

• cpe:2.3:a:ntp:ntp:*:*:*:*:*:*:*:*
• cpe:2.3:a:ntp:ntp:4.2.8:-:*:*:*:*:*:*
• cpe:2.3:a:ntp:ntp:4.2.8:p1:*:*:*:*:*:*
• cpe:2.3:a:ntp:ntp:4.2.8:p1-beta1:*:*:*:*:*:*
• cpe:2.3:a:ntp:ntp:4.2.8:p1-beta2:*:*:*:*:*:*
• cpe:2.3:a:ntp:ntp:4.2.8:p1-beta3:*:*:*:*:*:*
• cpe:2.3:a:ntp:ntp:4.2.8:p1-beta4:*:*:*:*:*:*
• cpe:2.3:a:ntp:ntp:4.2.8:p1-beta5:*:*:*:*:*:*
• cpe:2.3:a:ntp:ntp:4.2.8:p1-rc1:*:*:*:*:*:*
• cpe:2.3:a:ntp:ntp:4.2.8:p1-rc2:*:*:*:*:*:*
• cpe:2.3:a:ntp:ntp:4.2.8:p2:*:*:*:*:*:*
• cpe:2.3:a:ntp:ntp:4.2.8:p2-rc1:*:*:*:*:*:*
• cpe:2.3:a:ntp:ntp:4.2.8:p2-rc2:*:*:*:*:*:*
• cpe:2.3:a:ntp:ntp:4.2.8:p2-rc3:*:*:*:*:*:*
• cpe:2.3:a:ntp:ntp:4.2.8:p3:*:*:*:*:*:*
• cpe:2.3:a:ntp:ntp:4.2.8:p3-rc1:*:*:*:*:*:*
• cpe:2.3:a:ntp:ntp:4.2.8:p3-rc2:*:*:*:*:*:*
• cpe:2.3:a:ntp:ntp:4.2.8:p3-rc3:*:*:*:*:*:*
• cpe:2.3:a:ntp:ntp:4.2.8:p4:*:*:*:*:*:*
• cpe:2.3:a:ntp:ntp:4.2.8:p5:*:*:*:*:*:*
• cpe:2.3:a:ntp:ntp:4.2.8:p6:*:*:*:*:*:*
• cpe:2.3:a:ntp:ntp:4.2.8:p7:*:*:*:*:*:*
• cpe:2.3:o:oracle:solaris:10:*:*:*:*:*:*:*
• cpe:2.3:o:oracle:solaris:11.3:*:*:*:*:*:*:*
• cpe:2.3:a:suse:manager:2.1:*:*:*:*:*:*:*
• cpe:2.3:a:suse:manager_proxy:2.1:*:*:*:*:*:*:*
• cpe:2.3:a:suse:openstack_cloud:5:*:*:*:*:*:*:*
• cpe:2.3:o:opensuse:leap:42.1:*:*:*:*:*:*:*
• cpe:2.3:o:opensuse:opensuse:13.2:*:*:*:*:*:*:*
• cpe:2.3:o:suse:linux_enterprise_desktop:12:sp1:*:*:*:*:*:*
• cpe:2.3:o:suse:linux_enterprise_server:11:sp2:*:*:ltss:*:*:*
• cpe:2.3:o:suse:linux_enterprise_server:11:sp3:*:*:ltss:*:*:*
• cpe:2.3:o:suse:linux_enterprise_server:11:sp4:*:*:*:*:*:*
• cpe:2.3:o:suse:linux_enterprise_server:12:sp1:*:*:*:*:*:*
• cpe:2.3:o:siemens:simatic_net_cp_443-1_opc_ua_firmware:*:*:*:*:*:*:*:*
• cpe:2.3:o:siemens:tim_4r-ie_firmware:*:*:*:*:*:*:*:*
• cpe:2.3:o:siemens:tim_4r-ie_dnp3_firmware:*:*:*:*:*:*:*:*

More vulnerabilities in Ntp

• CVE-2018-12327 — Critical (CVSS 9.8): Stack-based buffer overflow in ntpq and ntpdc of NTP version 4.2.8p11 allows an attacker to achieve code execution or…
• CVE-2018-7183 — Critical (CVSS 9.8): Buffer overflow in the decodearr function in ntpq in ntp 4.2.8p6 through 4.2.8p10 allows remote attackers to execute…
• CVE-2015-7871 — Critical (CVSS 9.8): Crypto-NAK packets in ntpd in NTP 4.2.x before 4.2.8p4, and 4.3.x before 4.3.77 allows remote attackers to bypass…
• CVE-2015-7853 — Critical (CVSS 9.8): The datalen parameter in the refclock driver in NTP 4.2.x before 4.2.8p4, and 4.3.x before 4.3.77 allows remote…
• CVE-2015-7705 — Critical (CVSS 9.8): The rate limiting feature in NTP 4.x before 4.2.8p4 and 4.3.x before 4.3.77 allows remote attackers to have unspecified…
• CVE-2015-7854 — High (CVSS 8.8): Buffer overflow in the password management functionality in NTP 4.2.x before 4.2.8p4, and 4.3.x before 4.3.77 allows…

All CVEs affecting Ntp →

Other CWE-287 (Improper Authentication) vulnerabilities

• CVE-2026-45480 — Critical (CVSS 10.0): Improper authentication in Azure Active Directory allows an unauthorized attacker to elevate privileges over a network.
• CVE-2026-46389 — Critical (CVSS 10.0): UDS Identity Config builds the Keycloak configuration image (realm, plugins, theme, truststore, JARs) consumed by UDS…
• CVE-2026-10611 — Critical (CVSS 10.0): An authentication bypass vulnerability exists in MISP when LDAP mixed authentication is enabled with OTP enforcement.…
• CVE-2026-47280 — Critical (CVSS 10.0): Improper authentication in Azure Resource Manager (ARM) allows an unauthorized attacker to elevate privileges over a…
• CVE-2026-42822 — Critical (CVSS 10.0): Improper authentication in Azure Local Disconnected Operations allows an unauthorized attacker to elevate privileges…
• CVE-2026-20182 — Critical (CVSS 10.0): May 2026: This security advisory provides the details and fix information for a vulnerability that was discovered and…

Browse all CWE-287 (Improper Authentication) vulnerabilities →

Threat intelligence

Threat-intel indicators referencing this CVE:

• 197.248.207.139 (ipv4-addr)
• 135.129.128.247 (ipv4-addr)
• 119.201.59.224 (ipv4-addr)
• 42.200.60.186 (ipv4-addr)
• 223.197.153.135 (ipv4-addr)
• 125.212.244.35 (ipv4-addr)
• 202.29.220.126 (ipv4-addr)
• 93.42.227.251 (ipv4-addr)