---
id: CVE-2026-32665
title: Remote DNS-over-QUIC denial of service due to `quic-size` budget bypass
summary: >-
  In NLnet Labs Unbound 1.22.0 up to and including 1.25.1, when downstream
  DNS-over-QUIC (DoQ) is enabled, the first two bidirectional streams on a new
  QUIC connection (stream_id 0 and 4) bypass the per-stream 'quic-size' gate
  entirely, an…
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'
cvssSource: cna
cwe:
  - CWE-1284
vendor: NLnet Labs
product: Unbound
affected:
  - Unbound >= 1.22.0 < 1.25.2
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-07-22T14:31:54.691586Z'
published: '2026-07-22'
updated: '2026-09-16'
sourceUpdated: '2026-09-16T14:24:37.708Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-32665'
references:
  - url: 'https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-32665.txt'
tags:
  - cve.org
epss: 0.00471
epssPercentile: 0.38086
ingestedAt: '2026-09-16T14:57:28.057Z'
---

## Overview

In NLnet Labs Unbound 1.22.0 up to and including 1.25.1, when downstream DNS-over-QUIC (DoQ) is enabled, the first two bidirectional streams on a new QUIC connection (stream_id 0 and 4) bypass the per-stream 'quic-size' gate entirely, and large input buffers are allocated later, after only the 2-byte length prefix has been received from the initial streams. As a result, a remote client can make Unbound exceed the configured 'quic-size' limit with low-cost input. Using only one connection and two streams, each sending a declared 65535-byte length prefix and then holding the streams open, a client can already trivially make Unbound roughly allocate double that amount. This is a remote availability issue / memory-accounting bypass in the downstream DoQ implementation that leads to denial of service for new DoQ clients. This vulnerability needs Unbound to be compiled with DoQ support ('--with-libngtcp2') and the 'quic-port' to be configured for the listening interfaces.

## Affected

- `Unbound >= 1.22.0 < 1.25.2`

## Remediation

This issue is fixed starting with version 1.25.2