CVE-2026-32665

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.

CVSS v3 7.5 HIGH

7.5^/10

CVSS v3 : HIGH

Vector :

Exploitability : 3.9 / Impact : 3.6

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact NONE

Integrity Impact NONE

Availability Impact HIGH

Scope UNCHANGED

References

Link	Resource
https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-32665.txt	Vendor Advisory

Configurations

Configuration 1 (hide)

cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:*

History

24 Jul 2026, 13:57

Type	Values Removed	Values Added
References	~~() https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-32665.txt -~~	() https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-32665.txt - Vendor Advisory
CPE		cpe:2.3:a:nlnetlabs:unbound::::::::
First Time		Nlnetlabs Nlnetlabs unbound

22 Jul 2026, 14:17

Type	Values Removed	Values Added
New CVE

Information

Published : 2026-07-22 14:17

Updated : 2026-07-24 13:57

NVD link : CVE-2026-32665

Mitre link : CVE-2026-32665

CVE.ORG link : CVE-2026-32665

JSON object : View

Products Affected

nlnetlabs

unbound

CWE

CWE-1284

Improper Validation of Specified Quantity in Input

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