---
id: CVE-2026-121506
title: Out-of-bounds Write in NTPsec
summary: >-
  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, …
severity: high
cvss: 7.4
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:H'
cvssSource: cna
cwe:
  - CWE-787
vendor: NTPsec
product: NTPsec
affected:
  - NTPsec >= 1.1.4 < 1.2.5
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-11-03T15:15:17.727246Z'
published: '2026-11-03'
updated: '2026-11-03'
sourceUpdated: '2026-11-03T15:29:28.236Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-121506'
references:
  - url: >-
      https://gitlab.com/NTPsec/ntpsec/-/commit/0a36941e499d533dfbc3fb6b1fcd8c367679d719
  - url: 'https://gitlab.com/NTPsec/ntpsec/-/work_items/902'
tags:
  - cve.org
epss: 0.00449
epssPercentile: 0.39256
ingestedAt: '2026-11-05T19:30:42.986Z'
---

## Overview

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.

## Affected

- `NTPsec >= 1.1.4 < 1.2.5`

## Remediation

Upgrade to version 1.2.5 or above.