# CVE-2026-32665: NLnet Labs Unbound denial of service in DNS-over-QUIC

Source: https://junglewise.ai/threats/cve-2026-32665-nlnet-labs-unbound-denial-of-service-in-dns-over-quic  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-22. Updated: 2026-07-22  
License: CC BY 4.0 with a link back

CVE-2026-32665 · Severity: high · CVSS 7.5 · Published 2026-07-22

A vulnerability in the Unbound DNS resolver could allow an attacker to crash or disable the service by exhausting its memory. By sending specifically crafted requests using the DNS-over-QUIC protocol, a remote user can bypass security limits and force the server to allocate excessive resources. This results in a denial of service, preventing legitimate users from resolving domain names.

Technologies: [NLnet Labs Unbound](https://junglewise.ai/threats/technologies/unbound). Vendors: [NLnet Labs](https://junglewise.ai/threats/vendors/nlnet-labs).

## Quick answers

**Is CVE-2026-32665 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-32665 being exploited in the wild.

**How severe is CVE-2026-32665?** High severity, with a CVSS score of 7.5, published 22 July 2026.

**Which products and versions are affected?** NLnet Labs Unbound 1.22.0 through 1.25.1.

**Is there a fix for CVE-2026-32665?** A patch was published on 2026-07-22: Fixed in Unbound 1.25.2 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-32665 attacked?** It is attacked over the network, in a hosted service.

**Am I affected by CVE-2026-32665?** Check whether you run NLnet Labs Unbound at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A vulnerability exists in Unbound's downstream DNS-over-QUIC (DoQ) implementation where the first two bidirectional streams (IDs 0 and 4) of a new connection bypass the 'quic-size' memory limit validation. An attacker can send a 2-byte length prefix declaring a large payload (up to 65535 bytes) without actually sending the data, forcing Unbound to allocate large input buffers prematurely. By maintaining these open streams, a remote unauthenticated attacker can exceed configured memory budgets with minimal effort, leading to a denial of service for subsequent DoQ clients. This issue affects Unbound versions 1.22.0 through 1.25.1 when compiled with 'libngtcp2' and configured with a 'quic-port'. The vulnerability is addressed in version 1.25.2.

## Affected products

- NLnet Labs Unbound 1.22.0 through 1.25.1

## Timeline

- 2026-07-22: disclosed
- 2026-07-22: advisory
- 2026-07-22: patched: Fixed in Unbound 1.25.2

## References

- [https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-32665.txt](https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-32665.txt)

## Related threats

- [NLnet Labs Unbound use-after-free in DNS-over-QUIC stream cleanup](https://junglewise.ai/threats/cve-2026-97206-nlnet-labs-unbound-1-22-0-up-to-and-including-version-1-26-1)
- [NLnet Labs Unbound DNS decompression CPU exhaustion](https://junglewise.ai/threats/cve-2026-96405-nlnet-labs-unbound-up-to-and-including-version-1-26-1-limits)
- [NLnet Labs Unbound DNS validator bypass in DNSSEC validation](https://junglewise.ai/threats/cve-2026-50106-when-nlnet-labs-unbound-up-to-and-including-version-1-26-1-is)
- [NLnet Labs Unbound cache side-channel in upstream source port probe](https://junglewise.ai/threats/cve-2026-109125-in-nlnet-labs-unbound-up-to-and-including-version-1-26-1-an)
- [NLnet Labs Unbound DNS complexity attacks via ReTrap](https://junglewise.ai/threats/cve-2026-85501-nlnet-labs-unbound-dns-complexity-attacks-via-retrap)