What is CVE-2026-121506?

CVE-2026-121506 is a high-severity vulnerability in Ntpsec, classified under Out-of-bounds Write. CVSS score: 7.4/10. Published 2026-11-03.

How severe is CVE-2026-121506?

High severity. CVSS v3 base score is 7.4 out of 10.

Buffer overflow in Ntpsec

CVE-2026-121506

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.

Vulnerability class: Buffer Overflow

Published 2026-11-03 · last modified 2026-11-03.

CVSS v3 metric

CVSS v3 base score 7.4 (High). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:H.

EPSS exploit prediction

No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.

Affected products

Ntpsec

Weakness classification (CWE)

CWE-787 — Out-of-bounds Write

References

Frequently asked questions

What is CVE-2026-121506?: CVE-2026-121506 is a high-severity vulnerability in Ntpsec, classified under Out-of-bounds Write. CVSS score: 7.4/10. Published 2026-11-03.
How severe is CVE-2026-121506?: High severity. CVSS v3 base score is 7.4 out of 10.