Description
Buffer overflow in NTPsec's Zyfer refclock allows local attacker to crash ntpd
Published: 2026-07-31
Score: 4.7 Medium
EPSS: < 1% Very Low
KEV: No
Impact: n/a
Action: n/a
AI Analysis

Impact

A classic buffer overflow in the Zyfer refclock component of NTPsec allows an attacker with local access to trigger an unsafe copy operation. This flaw falls under CWE‑120 and can cause the ntpd daemon to crash, leading to a denial of service for clients that rely on accurate time synchronization.

Affected Systems

All deployable releases of the NTPsec package that include the Zyfer refclock module before version 1.2.5 are affected. The vulnerability is present in every earlier build that has not applied the update that removes the unsafe code path.

Risk and Exploitability

The CVSS score of 4.7 reflects moderate severity, while the EPSS score of less than 1% indicates a very low likelihood of exploitation in the wild. The vulnerability is not listed in CISA’s KEV catalog. The most likely attack vector is local execution with sufficient privileges to interact with the refclock interface, requiring the attacker to be able to run code on the affected host.

Generated by OpenCVE AI on August 3, 2026 at 09:51 UTC.

Remediation

Vendor Solution

Upgrade to version 1.2.5

OpenCVE Recommended Actions

  • Upgrade NTPsec to version 1.2.5 or later, which contains a fix for the buffer overflow in the Zyfer refclock module.
  • If an upgrade is not immediately possible, remove or comment out the Zyfer refclock configuration in ntpd’s settings to eliminate the vulnerable code path.
  • Restrict local users’ ability to modify the NTP configuration and to invoke the refclock interface by tightening file permissions and using sudo or other privilege‑management mechanisms to limit access to trusted administrators.

Generated by OpenCVE AI on August 3, 2026 at 09:51 UTC.

Tracking

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Advisories

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History

Wed, 12 Aug 2026 12:15:00 +0000

Type Values Removed Values Added
References
Metrics threat_severity

None

 threat_severity

Low

Fri, 31 Jul 2026 19:45:00 +0000

Type Values Removed Values Added
First Time appeared Ntpsec
Ntpsec ntpsec
Vendors & Products Ntpsec
Ntpsec ntpsec

Fri, 31 Jul 2026 19:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Fri, 31 Jul 2026 18:45:00 +0000

Type Values Removed Values Added
Description Buffer overflow in NTPsec's Zyfer refclock allows local attacker to crash ntpd
Title Buffer Copy without Checking Size of Input ('Classic Buffer Overflow') in ntpsec
Weaknesses CWE-120
References
Metrics cvssV3_1

{'score': 4.7, 'vector': 'CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H'}

Subscriptions

Ntpsec Ntpsec
cve-icon MITRE

Status: PUBLISHED

Assigner: GitLab

Published:

Updated: 2026-07-31T18:54:10.546Z

Reserved: 2026-07-29T19:04:09.259Z

Link: CVE-2026-18321

cve-icon Vulnrichment

Updated: 2026-07-31T18:54:05.907Z

cve-icon NVD

Status : Received

Published: 2026-07-31T19:17:08.183

Modified: 2026-07-31T19:17:08.183

Link: CVE-2026-18321

cve-icon Redhat

Severity : Low

Publid Date: 2026-07-31T18:04:06Z

Links: CVE-2026-18321 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-08-03T10:00:12Z

Weaknesses
  • CWE-120

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