---
id: CVE-2026-19401
title: >-
  Any remote client can crash a (debugging/non-release build type) NSD serve
  child by sending it a special crafted message with a specially tuned number of
  DNS Cookie options (17 when UDP payload size is 512)
summary: >-
  Any remote client can crash a (debugging/non-release build type) NSD serve
  child by sending it a special crafted message with a specially tuned number of
  DNS Cookie options (17 when UDP payload size is 512). By continuously crashing
  the …
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-400
  - CWE-617
vendor: nlnetlabs
product: nsd
affected:
  - 'nsd >= 4.3.7, < 4.15.1'
patched:
  - nsd 4.15.1
published: '2026-08-26'
updated: '2026-09-08'
sourceUpdated: '2026-09-08T20:00:05.427'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-19401'
references:
  - url: 'https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-19401.txt'
    label: sep@nlnetlabs.nl
tags:
  - nvd
epss: 0.00281
epssPercentile: 0.18233
ingestedAt: '2026-09-08T20:10:03.158Z'
---

## Overview

Any remote client can crash a (debugging/non-release build type) NSD serve child by sending it a special crafted message with a specially tuned number of DNS Cookie options (17 when UDP payload size is 512). By continuously crashing the serve childs, the remote client can severely hamper or, when positioned sufficiently close, deny all DNS service.

## Affected

- `nsd >= 4.3.7, < 4.15.1`

## Remediation

Upgrade past the affected range:

- `nsd 4.15.1`