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CVE-2016-4953

ntpd in NTP 4.x before 4.2.8p8 allows remote attackers to cause a denial of service (ephemeral...

7.5 HighFix available

CVE-2016-4953 is a high vulnerability (CVSS 7.5) in Ntp, published June 13, 2016. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 17.2%, the 97th percentile. Fixed in ntp 1:4.2.8p8+dfsg-1.

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.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
None
Integrity
None
Availability
High

Exploit likelihood

17.2%Up 12.9 points since Feb 4, 2022
90%50%10%1%

What each source reports

NVD Score used 7.5

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.

Record
CVE-2016-4953
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS 2.0
5.0 MediumAV:N/AC:L/Au:N/C:N/I:N/A:P
Weakness
CWE-287
Updated
2026-11-02
CVE List No score

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.

Record
CVE-2016-4953
Updated
2026-11-02
EUVDEUVD-2016-5927 No score

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.

Record
EUVD-2016-5927
Updated
2026-11-03
GitHub AdvisoriesGHSA-26jw-7mv6-89rj 7.5

ntpd in NTP 4.x before 4.2.8p8 allows remote attackers to cause a denial of service (ephemeral...

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.

Record
GHSA-26jw-7mv6-89rj
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-287
Updated
2026-11-02
OSV 7.5

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.

Record
CVE-2016-4953
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02
OSVDEBIAN-CVE-2016-4953 7.5

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.

Record
DEBIAN-CVE-2016-4953
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02
Show 5 moreShow less
OSVopenSUSE-SU-2024:10181-1 No score

ntp-4.2.8p9-1.1 on GA media

These are all security issues fixed in the ntp-4.2.8p9-1.1 package on the GA media of openSUSE Tumbleweed.

Record
openSUSE-SU-2024:10181-1
Updated
2026-11-02
OSVSUSE-SU-2016:1563-1 No score

Security update for ntp

ntp was updated to version 4.2.8p8 to fix five security issues.

These security issues were fixed:

  • CVE-2016-4953: Bad authentication demobilizes ephemeral associations (bsc#982065).
  • CVE-2016-4954: Processing spoofed server packets (bsc#982066).
  • CVE-2016-4955: Autokey association reset (bsc#982067).
  • CVE-2016-4956: Broadcast interleave (bsc#982068).
  • CVE-2016-4957: CRYPTO_NAK crash (bsc#982064).

These non-security issues were fixed:

  • Keep the parent process alive until the daemon has finished initialisation, to make sure that the PID file exists when the parent returns.
  • bsc#979302: Change the process name of the forking DNS worker process to avoid the impression that ntpd is started twice.
  • bsc#981422: Don't ignore SIGCHILD because it breaks wait().
  • bsc#979981: ntp-wait does not accept fractional seconds, so use 1 instead of 0.2 in ntp-wait.service.
  • Separate the creation of ntp.keys and key #1 in it to avoid problems when upgrading installations that have the file, but no key #1, which is needed e.g. by 'rcntp addserver'.
Record
SUSE-SU-2016:1563-1
Updated
2026-11-02
OSVSUSE-SU-2016:1568-1 No score

Security update for ntp

ntp was updated to version 4.2.8p8 to fix 17 security issues.

These security issues were fixed:

  • CVE-2016-4956: Broadcast interleave (bsc#982068).
  • CVE-2016-2518: Crafted addpeer with hmode > 7 causes array wraparound with MATCH_ASSOC (bsc#977457).
  • CVE-2016-2519: ctl_getitem() return value not always checked (bsc#977458).
  • CVE-2016-4954: Processing spoofed server packets (bsc#982066).
  • CVE-2016-4955: Autokey association reset (bsc#982067).
  • CVE-2015-7974: NTP did not verify peer associations of symmetric keys when authenticating packets, which might allowed remote attackers to conduct impersonation attacks via an arbitrary trusted key, aka a 'skeleton key (bsc#962960).
  • CVE-2016-4957: CRYPTO_NAK crash (bsc#982064).
  • CVE-2016-2516: Duplicate IPs on unconfig directives will cause an assertion botch (bsc#977452).
  • CVE-2016-2517: Remote configuration trustedkey/requestkey values are not properly validated (bsc#977455).
  • CVE-2016-4953: Bad authentication demobilizes ephemeral associations (bsc#982065).
  • CVE-2016-1547: CRYPTO-NAK DoS (bsc#977459).
  • CVE-2016-1551: Refclock impersonation vulnerability, AKA: refclock-peering (bsc#977450).
  • CVE-2016-1550: Improve NTP security against buffer comparison timing attacks, authdecrypt-timing, AKA: authdecrypt-timing (bsc#977464).
  • CVE-2016-1548: Interleave-pivot - MITIGATION ONLY (bsc#977461).
  • CVE-2016-1549: Sybil vulnerability: ephemeral association attack, AKA: ntp-sybil - MITIGATION ONLY (bsc#977451).

This release also contained improved patches for CVE-2015-7704, CVE-2015-7705, CVE-2015-7974.

These non-security issues were fixed:

  • bsc#979302: Change the process name of the forking DNS worker process to avoid the impression that ntpd is started twice.
  • bsc#981422: Don't ignore SIGCHILD because it breaks wait().
  • bsc#979981: ntp-wait does not accept fractional seconds, so use 1 instead of 0.2 in ntp-wait.service.
  • Separate the creation of ntp.keys and key #1 in it to avoid problems when upgrading installations that have the file, but no key #1, which is needed e.g. by 'rcntp addserver'.
  • bsc#957226: Restrict the parser in the startup script to the first occurrance of 'keys' and 'controlkey' in ntp.conf.
Record
SUSE-SU-2016:1568-1
Updated
2026-11-02
OSVSUSE-SU-2016:1584-1 No score

Security update for ntp

ntp was updated to version 4.2.8p8 to fix five security issues.

These security issues were fixed:

  • CVE-2016-4953: Bad authentication demobilizes ephemeral associations (bsc#982065).
  • CVE-2016-4954: Processing spoofed server packets (bsc#982066).
  • CVE-2016-4955: Autokey association reset (bsc#982067).
  • CVE-2016-4956: Broadcast interleave (bsc#982068).
  • CVE-2016-4957: CRYPTO_NAK crash (bsc#982064).

These non-security issues were fixed:

  • Keep the parent process alive until the daemon has finished initialisation, to make sure that the PID file exists when the parent returns.
  • bsc#979302: Change the process name of the forking DNS worker process to avoid the impression that ntpd is started twice.
  • bsc#981422: Don't ignore SIGCHILD because it breaks wait().
  • Separate the creation of ntp.keys and key #1 in it to avoid problems when upgrading installations that have the file, but no key #1, which is needed e.g. by 'rcntp addserver'.
Record
SUSE-SU-2016:1584-1
Updated
2026-11-02
OSVSUSE-SU-2016:1602-1 No score

Security update for ntp

ntp was updated to version 4.2.8p8 to fix five security issues.

These security issues were fixed:

  • CVE-2016-4953: Bad authentication demobilizes ephemeral associations (bsc#982065).
  • CVE-2016-4954: Processing spoofed server packets (bsc#982066).
  • CVE-2016-4955: Autokey association reset (bsc#982067).
  • CVE-2016-4956: Broadcast interleave (bsc#982068).
  • CVE-2016-4957: CRYPTO_NAK crash (bsc#982064).

These non-security issues were fixed:

  • Keep the parent process alive until the daemon has finished initialisation, to make sure that the PID file exists when the parent returns.
  • bsc#979302: Change the process name of the forking DNS worker process to avoid the impression that ntpd is started twice.
  • bsc#981422: Don't ignore SIGCHILD because it breaks wait().
Record
SUSE-SU-2016:1602-1
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
ntp
Debian:11
 before 1:4.2.8p8+dfsg-1
1:4.2.8p8+dfsg-1
ntp
SUSE:Linux Enterprise Desktop 12 SP1
 before 4.2.8p8-14.1
4.2.8p8-14.1
ntp
SUSE:Linux Enterprise Server 12 SP1
 before 4.2.8p8-14.1
4.2.8p8-14.1
ntp
SUSE:Linux Enterprise Server for SAP Applications 12 SP1
 before 4.2.8p8-14.1
4.2.8p8-14.1
ntp
SUSE:Linux Enterprise Desktop 12
 before 4.2.8p8-46.8.1
4.2.8p8-46.8.1
ntp
SUSE:Linux Enterprise Server 12
 before 4.2.8p8-46.8.1
4.2.8p8-46.8.1
ntp
SUSE:Linux Enterprise Server for SAP Applications 12
 before 4.2.8p8-46.8.1
4.2.8p8-46.8.1
ntp
SUSE:Linux Enterprise Server 11 SP4
 before 4.2.8p8-14.1
4.2.8p8-14.1
ntp
SUSE:Linux Enterprise Server for SAP Applications 11 SP4
 before 4.2.8p8-14.1
4.2.8p8-14.1
ntp
SUSE:OpenStack Cloud 5
 before 4.2.8p8-47.3
4.2.8p8-47.3
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Affected packages
PackageAffectedFixed
ntp
SUSE:Manager 2.1
 before 4.2.8p8-47.3
4.2.8p8-47.3
ntp
SUSE:Manager Proxy 2.1
 before 4.2.8p8-47.3
4.2.8p8-47.3
ntp
SUSE:Linux Enterprise Server 11 SP2-LTSS
 before 4.2.8p8-47.3
4.2.8p8-47.3
ntp
SUSE:Linux Enterprise Server 11 SP3-LTSS
 before 4.2.8p8-47.3
4.2.8p8-47.3
ntp
SUSE:Linux Enterprise Server 11 SP3-TERADATA
 before 4.2.8p8-47.3
4.2.8p8-47.3
ntp
openSUSE:Tumbleweed
 before 4.2.8p9-1.1
4.2.8p9-1.1

History

History
WhenChangedSources
2026-11-03aliasesEUVD
2026-11-02createdCVE List, GitHub Advisories, NVD, OSV

References

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