---
id: "CVE-2026-121505"
kind: "vulnerability"
aliases: ["CVE-2026-121505"]
title: "NTPsec: NTS client over-reads memory and leaks pointers to servers"
severity: "low"
cvss: 3.7
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["ntp", "ntpsec", "nts", "package", "time-sync"]
not_affected_if: ["no-nts-client", "trusted-nts-servers-only"]
published_at: "2026-11-03T15:17:37+00:00"
first_seen_at: "2026-11-03T15:22:01+00:00"
updated_at: "2026-11-03T15:24:47+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-121505", "first_seen_at": "2026-11-03T15:22:01+00:00"}]
---

# NTPsec: NTS client over-reads memory and leaks pointers to servers

A bug in NTPsec's NTS-KE client response parser lets a malicious NTS-KE server make the client read past its buffer. The client then sends that stack memory, including pointers that weaken ASLR, back in cleartext as NTS cookies.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the installed NTPsec version with `ntpq --version` or `ntpd --version`
- Look for NTS client use in the NTP configuration (`nts` keyword in ntp.conf or ntpsec config)

## Fix

- NTPsec `1.2.4` or later (the advisory states fixes start at `before 1.2.4`)

## Timeline

- 2026-11-03T15:22:01+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-121505

## From the sources

An out-of-bounds read in the NTS-KE client response parser (nts_client_process_response_core) in NTPsec before 1.2.4 allows a malicious NTS-KE server to read the client's stack memory, including pointers that defeat ASLR, which the client then sends in cleartext as NTS cookies, via an NTS-KE record whose declared length exceeds the data received.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_