# CVE-2026-121506: Out-of-bounds Write in NTPsec

Status: published. Published: 2026-11-03. Updated: 2026-11-03.

An out-of-bounds read and write in NTS client extension field parsing (extens_client_recv) in NTPsec before 1.2.5 allows a remote attacker who can send NTP server-mode replies to an NTS client to corrupt heap memory and crash ntpd, and, combined with the NTS-KE client out-of-bounds read fixed in 1.2.4, to bypass NTS authentication and set the client's time, via an NTS Authenticator and Encrypted Extension Fields field whose nonce length exceeds the field.

## Remediation

- fix: Upgrade to version 1.2.5 or above. (source: CNA: GitLab)

## Affected products and versions

- NTPsec / NTPsec: ≥ 1.1.4; < 1.2.5 (affected, semver). Source: CNA: GitLab

## Severity and prioritization

- CVSS 3.1: 7.4 (high); CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:H; source: CNA: GitLab

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-787

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://gitlab.com/NTPsec/ntpsec/-/commit/0a36941e499d533dfbc3fb6b1fcd8c367679d719 (CNA: GitLab)

- https://gitlab.com/NTPsec/ntpsec/-/work_items/902 (CNA: GitLab)

## Provenance

- CNA: GitLab: https://www.cve.org/CVERecord?id=CVE-2026-121506; retrieved 2026-11-03; source updated 2026-11-03

Revision: 195f1601b7a3b6643688ef36db212113d9276f4184370af8f5a789a70a45af24

Canonical: https://y2.dev/cve/CVE-2026-121506

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