CVE-2016-4955

CVE-2016-4955 is a medium-severity vulnerability in Ntp with a CVSS 3.x base score of 5.9. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-362.

Key facts

• Severity: Medium (CVSS 3.x base score 5.9)
• CVSS v2: 4.3
• EPSS exploit prediction: 9% (95th percentile)
• Actively exploited: Not listed in CISA KEV
• Weakness: CWE-362
• Affected product: Ntp
• Published: 2016-07-05
• Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is 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.

How severe is CVE-2016-4955?

CVE-2016-4955 has a CVSS 3.x base score of 5.9, rated medium severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2016-4955 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 9% (95th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2016-4955?

CVE-2016-4955 primarily affects Ntp. In total, 35 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2016-4955?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2016-4955 published?

CVE-2016-4955 was published on 2016-07-05 and last updated on 2026-06-17.

References

• http://bugs.ntp.org/3043
• 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/NtpBug3043
• 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/archive/1/538599/100/0/threaded
• http://www.securityfocus.com/archive/1/archive/1/538600/100/0/threaded
• http://www.securityfocus.com/bid/91007
• http://www.securitytracker.com/id/1036037
• http://www.ubuntu.com/usn/USN-3096-1
• https://cert-portal.siemens.com/productcert/pdf/ssa-211752.pdf
• 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
• https://security.gentoo.org/glsa/201607-15
• https://us-cert.cisa.gov/ics/advisories/icsa-21-159-11

Affected products (35)

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

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-362 (Race Condition) vulnerabilities

• CVE-2022-27626 — Critical (CVSS 10.0): A vulnerability regarding concurrent execution using shared resource with improper synchronization ('Race Condition')…
• CVE-2015-8556 — Critical (CVSS 10.0): Local privilege escalation vulnerability in the Gentoo QEMU package before 2.5.0-r1.
• CVE-2014-0703 — Critical (CVSS 10.0): Cisco Wireless LAN Controller (WLC) devices 7.4 before 7.4.110.0 distribute Aironet IOS software with a race condition…
• CVE-2010-1228 — Critical (CVSS 10.0): Multiple race conditions in the sandbox infrastructure in Google Chrome before 4.1.249.1036 have unspecified impact and…
• CVE-2008-6598 — Critical (CVSS 10.0): Multiple race conditions in WANPIPE before 3.3.6 have unknown impact and attack vectors related to "bri restart logic."
• CVE-2026-46137 — Critical (CVSS 9.8): In the Linux kernel, the following vulnerability has been resolved: mptcp: pm: ADD_ADDR rtx: fix potential…

Browse all CWE-362 (Race Condition) 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)