CVE-2026-18321

Buffer Copy without Checking Size of Input ('Classic Buffer Overflow') in ntpsec

4.7 MediumFix available

Buffer overflow in NTPsec's Zyfer refclock allows local attacker to crash ntpd

Attack profile

How easy it is to exploit

Attack vector: Local
Complexity: High
Privileges needed: Low
User interaction: None

What an attacker can affect

Confidentiality: None
Integrity: None
Availability: High

Exploit likelihood

0.11%Unchanged since Aug 1, 2026

What each source reports

CVE List Score used 4.7

Buffer Copy without Checking Size of Input ('Classic Buffer Overflow') in ntpsec

Buffer overflow in NTPsec's Zyfer refclock allows local attacker to crash ntpd

Record: CVE-2026-18321
CVSS 3.1: 4.7 MediumCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
Weakness: CWE-120
Updated: 2026-11-02

EUVDEUVD-2026-51593 4.7

Buffer overflow in NTPsec's Zyfer refclock allows local attacker to crash ntpd

Record: EUVD-2026-51593
CVSS 3.1: 4.7 MediumCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
Updated: 2026-11-02

GitHub AdvisoriesGHSA-6978-pcpc-2c45 4.7

Buffer overflow in NTPsec's Zyfer refclock allows local attacker to crash ntpd

Buffer overflow in NTPsec's Zyfer refclock allows local attacker to crash ntpd

Record: GHSA-6978-pcpc-2c45
CVSS 3.1: 4.7 MediumCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
Weakness: CWE-120
Updated: 2026-11-02

NVD 4.7

Buffer overflow in NTPsec's Zyfer refclock allows local attacker to crash ntpd

Record: CVE-2026-18321
CVSS 3.1: 4.7 MediumCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
Weakness: CWE-120
Updated: 2026-11-02

OSVALPINE-CVE-2026-18321 4.7

Buffer overflow in NTPsec's Zyfer refclock allows local attacker to crash ntpd

Record: ALPINE-CVE-2026-18321
CVSS 3.1: 4.7 MediumCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
Updated: 2026-11-03

OSVDEBIAN-CVE-2026-18321 4.7

Buffer overflow in NTPsec's Zyfer refclock allows local attacker to crash ntpd

Record: DEBIAN-CVE-2026-18321
CVSS 3.1: 4.7 MediumCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
Updated: 2026-11-02

OSVUBUNTU-CVE-2026-18321 4.7

Buffer overflow in NTPsec's Zyfer refclock allows local attacker to crash ntpd

Record: UBUNTU-CVE-2026-18321
CVSS 3.1: 4.7 MediumCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
Updated: 2026-11-02

OSVMGASA-2026-0430 No score

Updated ntpsec packages fix a security vulnerability

Buffer Copy without Checking Size of Input ('Classic Buffer Overflow') in ntpsec. (CVE-2026-18321)

Record: MGASA-2026-0430
Updated: 2026-11-02

OSVopenSUSE-SU-2026:11417-1 No score

libntpc1-1.2.5-1.1 on GA media

These are all security issues fixed in the libntpc1-1.2.5-1.1 package on the GA media of openSUSE Tumbleweed.

Record: openSUSE-SU-2026:11417-1
Updated: 2026-11-02

Affected products

ntpsec

Affected packages

Affected packages
Package	Affected	Fixed
`ntpsec` Alpine:v3.24	before 1.2.5-r0	1.2.5-r0
`ntpsec` Debian:12	All versions, plus listed versions 1.2.2+dfsg1-11.2.2+dfsg1-1+deb12u11.2.2+dfsg1-21.2.2+dfsg1-31.2.2+dfsg1-4 Show 10 moreShow less 1.2.3+dfsg1-11.2.3+dfsg1-21.2.3+dfsg1-31.2.3+dfsg1-41.2.3+dfsg1-51.2.3+dfsg1-61.2.3+dfsg1-71.2.3+dfsg1-81.2.4+dfsg-11.2.5+dfsg-1	None known
`ntpsec` Debian:13	All versions, plus listed versions 1.2.3+dfsg1-81.2.4+dfsg-11.2.5+dfsg-1	None known
`ntpsec` Debian:14	before 1.2.5+dfsg-1, plus listed versions 1.2.3+dfsg1-81.2.4+dfsg-1	1.2.5+dfsg-1
`ntpsec` Mageia:10	before 1.2.4-3.2.mga10	1.2.4-3.2.mga10
`ntpsec` Mageia:9	before 1.2.2-5.1.mga9	1.2.2-5.1.mga9
`ntpsec` Ubuntu:18.04:LTS	All versions, plus listed versions 1.0.0+dfsg1-11.0.0+dfsg1-31.1.0+dfsg1-11.1.0+dfsg1-1ubuntu0.11.1.0+dfsg1-1ubuntu0.2	None known
`ntpsec` Ubuntu:20.04:LTS	All versions, plus listed versions 1.1.3+dfsg1-21.1.7+dfsg1-11.1.7+dfsg1-21.1.8+dfsg1-11.1.8+dfsg1-31.1.8+dfsg1-41.1.8+dfsg1-4build1	None known
`ntpsec` Ubuntu:22.04:LTS	All versions, plus listed versions 1.2.0+dfsg1-41.2.1+dfsg1-21.2.1+dfsg1-31.2.1+dfsg1-3ubuntu11.2.1+dfsg1-4	None known
`ntpsec` Ubuntu:24.04:LTS	All versions, plus listed versions 1.2.2+dfsg1-21.2.2+dfsg1-31.2.2+dfsg1-41.2.2+dfsg1-4build11.2.2+dfsg1-4build2	None known
`ntpsec` Ubuntu:26.10	All versions, plus listed versions 1.2.3+dfsg1-8ubuntu21.2.3+dfsg1-8ubuntu3	None known
`ntpsec` Ubuntu:26.04:LTS	All versions, plus listed versions 1.2.3+dfsg1-8ubuntu11.2.3+dfsg1-8ubuntu2	None known
`ntpsec` openSUSE:Tumbleweed	before 1.2.5-1.1	1.2.5-1.1

History

History
Recorded	Changed	Sources
Nov 3, 2026	affected, aliases, references	OSV
Nov 2, 2026	first indexed	CVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-18321 is a medium vulnerability (CVSS 4.7) in Ntpsec, published July 31, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.11%, the 1st percentile. Fixed in ntpsec 1.2.5-r0.

References

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