# CVE-2026-32665: Remote DNS-over-QUIC denial of service due to `quic-size` budget bypass

CVE-2026-32665 is fixed in 5 products on 1 platform, first by DEBIAN-CVE-2026-32665, released July 28, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-32665
- Priority: High
- CVSS: 7.5 (Moderate)
- EPSS: 0.0029
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jul 22, 2026
- Weakness: Improper Validation of Specified Quantity in Input
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-32665

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | libunbound8 Ubuntu 26.04.1 LTS (resolute) | 1.24.2-1ubuntu2.4 | [libunbound8 1.24.2-1ubuntu2.4](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-libunbound8-1.24.2-1ubuntu2.4.md) | Sep 16, 2026 |
| Linux | python3-unbound Ubuntu 26.04.1 LTS (resolute) | 1.24.2-1ubuntu2.4 | [python3-unbound 1.24.2-1ubuntu2.4](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-python3-unbound-1.24.2-1ubuntu2.4.md) | Sep 16, 2026 |
| Linux | unbound Debian 13.5 (trixie) | 1.26.1-0+deb13u1 | [DEBIAN-CVE-2026-32665](https://patchblox.com/security/data/fix/linux/debian-cve-2026-32665.md) | Jul 28, 2026 |
| Linux | unbound Debian 14 | 1.25.2-1 | [DEBIAN-CVE-2026-32665](https://patchblox.com/security/data/fix/linux/debian-cve-2026-32665.md) | Jul 28, 2026 |
| Linux | unbound Ubuntu 26.04.1 LTS (resolute) | 1.24.2-1ubuntu2.4 | [unbound 1.24.2-1ubuntu2.4](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-unbound-1.24.2-1ubuntu2.4.md) | Sep 16, 2026 |
| Linux | unbound opensuse-leap 16.0 | 1.25.2-160000.1.1 | [OPENSUSE-SU-2026:21550-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-21550-1.md) | Aug 10, 2026 |
| Linux | unbound sles 16.0 | 1.25.2-160000.1.1 | [SUSE-SU-2026:23226-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-23226-1.md) | Aug 10, 2026 |
| Linux | unbound-anchor Ubuntu 26.04.1 LTS (resolute) | 1.24.2-1ubuntu2.4 | [unbound-anchor 1.24.2-1ubuntu2.4](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-unbound-anchor-1.24.2-1ubuntu2.4.md) | Sep 16, 2026 |
| Linux | unbound-host Ubuntu 26.04.1 LTS (resolute) | 1.24.2-1ubuntu2.4 | [unbound-host 1.24.2-1ubuntu2.4](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-unbound-host-1.24.2-1ubuntu2.4.md) | Sep 16, 2026 |

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Data as of 2026-11-08T06:59:42Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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