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

> A local attacker can crash the NTPsec daemon via a buffer overflow in the Zyfer refclock driver, requiring that specific hardware driver to be enabled.

- **Severity:** Medium 4.7 (`CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 31 Jul 2026
- **Updated:** 31 Jul 2026
- **Also known as:** DEBIAN-CVE-2026-18321, GHSA-6978-pcpc-2c45, MGASA-2026-0430, MINI-w8x7-hxqv-7qw4, UBUNTU-CVE-2026-18321, openSUSE-SU-2026:11417-1

## What is CVE-2026-18321?

CVE-2026-18321 is a medium-severity memory corruption vulnerability in ntpsec, published on 31 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

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

Weakness: CWE-120 (Buffer Copy without Checking Size of Input)

## Which versions are affected by CVE-2026-18321?


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `ntpsec` | openSUSE:Tumbleweed | All versions | 1.2.5-1.1 |

## How do I fix CVE-2026-18321?

Apply the vendor's patch.

## Is CVE-2026-18321 being exploited?

There is no known exploitation of CVE-2026-18321 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-18321 and fix it if it is affected.

What it is: CVE-2026-18321 is a medium-severity memory corruption vulnerability in ntpsec, published on 31 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-18321 in the wild and no public exploit code.

Affected product: ntpsec. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-18321/ (Markdown: https://insights.sbomify.com/CVE-2026-18321/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-18321
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-18321
- OSV: https://osv.dev/vulnerability/CVE-2026-18321

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-18321/
Summaries are generated and may contain mistakes; the official description above is the record.