---
id: CVE-2026-101338
title: >-
  When a SVCB or HTTPS RR has filled the wire format RDATA up to the brim,
  another ECH parameter may overwrite the stack, and once beyond the limit, the
  base64 decoder can write attacker controlled data of unlimited size
summary: >-
  When a SVCB or HTTPS RR has filled the wire format RDATA up to the brim,
  another ECH parameter may overwrite the stack, and once beyond the limit, the
  base64 decoder can write attacker controlled data of unlimited size.  Zone
  files which…
severity: high
cvss: 8.7
cvssVector: 'CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N'
cwe:
  - CWE-121
vendor: NLnet Labs
product: NSD
affected:
  - NSD >= 4.10.0 < 4.15.3
published: '2026-10-14'
updated: '2026-10-16'
sourceUpdated: '2026-10-16T19:55:59.740'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-101338'
references:
  - url: 'https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-101338.txt'
    label: sep@nlnetlabs.nl
tags:
  - nvd
  - cve.org
epss: 0.0034
epssPercentile: 0.27374
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: total
  timestamp: '2026-10-14T14:09:10.026829Z'
cvssSource: cna
ingestedAt: '2026-10-14T11:27:22.140Z'
---

## Overview

When a SVCB or HTTPS RR has filled the wire format RDATA up to the brim, another ECH parameter may overwrite the stack, and once beyond the limit, the base64 decoder can write attacker controlled data of unlimited size.  Zone files which are written out by NSD itself, such as for zones for which the NSD instance is secondary, will not be formatted like this. The zone file must be fed to NSD directly, (but it could come, for example, from an operator controlled provisioning system).

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.