NLnet Labs Unbound up to 1.25.1 Downstream DoQ Implementation allocation of resources

Summaryinfo

A vulnerability, which was classified as critical, was found in NLnet Labs Unbound up to 1.25.1. This impacts an unknown function of the component Downstream DoQ Implementation. The manipulation results in allocation of resources. This vulnerability is cataloged as CVE-2026-32665. The attack may be launched remotely. There is no exploit available.

Detailsinfo

A vulnerability, which was classified as critical, was found in NLnet Labs Unbound up to 1.25.1. Affected is some unknown functionality of the component Downstream DoQ Implementation. The manipulation with an unknown input leads to a allocation of resources vulnerability. CWE is classifying the issue as CWE-770. The product allocates a reusable resource or group of resources on behalf of an actor without imposing any restrictions on the size or number of resources that can be allocated, in violation of the intended security policy for that actor. This is going to have an impact on availability. CVE summarizes:

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.

The advisory is available at nlnetlabs.nl. This vulnerability is traded as CVE-2026-32665 since 05/07/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. The technical details are unknown and an exploit is not available. This vulnerability is assigned to T1499 by the MITRE ATT&CK project.

Upgrading to version 1.25.2 eliminates this vulnerability.

If you want to get best quality of vulnerability data, you may have to visit VulDB.

Productinfo

Vendor

• NLnet Labs

Name

• Unbound

Version

• 1.25.0
• 1.25.1

CPE 2.3info

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CPE 2.2info

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If you want to get best quality of vulnerability data, you may have to visit VulDB.

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