CVE-2026-32665

Remote DNS-over-QUIC denial of service due to `quic-size` budget bypass

Published Jul 22, 2026 CVSS 3.1 · 7.5 High EPSS < 1% KEV · Not listed
Description
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.

Remediation

Vendor Solution

This issue is fixed starting with version 1.25.2

Tracking

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Advisories

Source ID Title
Debian DSA Debian DSA DSA-6507-1 unbound security update
Ubuntu USN Ubuntu USN USN-8946-1 Unbound vulnerabilities
Ubuntu USN Ubuntu USN USN-8946-2 Unbound vulnerabilities
History
Type Values Removed Values Added
First Time appeared Redhat
Redhat hummingbird
Weaknesses CWE-770
CPEs cpe:/a:redhat:hummingbird:1
Vendors & Products Redhat
Redhat hummingbird
References
Metrics threat_severity

None

threat_severity

Important

Type Values Removed Values Added
First Time appeared Nlnetlabs
Nlnetlabs unbound
Vendors & Products Nlnetlabs
Nlnetlabs unbound
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
Description 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.
Title Remote DNS-over-QUIC denial of service due to `quic-size` budget bypass
Weaknesses CWE-1284
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
NLnet Labs
Published
Updated
Sep 16, 2026, 2:24 PM
Reserved
May 7, 2026, 10:07 AM
Status
Analyzed
Published
Jul 22, 2026, 2:17 PM
Modified
Oct 24, 2026, 1:10 PM
Severity
Important
Public date
Jul 22, 2026, 12:00 AM