# CVE-2026-14586: Assertion in libngtcp2 when under pressure in high concurrency DNS-over-QUIC environments

CVE-2026-14586 is fixed in unbound on 1 platform, first by DEBIAN-CVE-2026-14586, released July 28, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-14586
- Priority: Routine
- CVSS: 5.9 (Moderate)
- EPSS: 0.0037
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jul 22, 2026
- Weakness: Reachable Assertion
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-14586

## Description

In NLnet Labs Unbound 1.22.0 up to and including 1.25.1, in DNS-over-QUIC environments, with high concurrency and under pressure, an assertion in libngtcp2 about monotonic timestamps could trigger and result in server termination and thus denial of service. When interfacing with libngtcp2, for DNS-over-QUIC support in Unbound, it is expected to use monotonic time. Unbound was using realtime instead, and in DoQ environments with high concurrency and under pressure, an assert in libngtcp2 for the quic timestamp would trigger and terminate the server.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 | unbound Debian 13.5 (trixie) | 1.26.1-0+deb13u1 | [DEBIAN-CVE-2026-14586](https://patchblox.com/security/data/fix/linux/debian-cve-2026-14586.md) | Jul 28, 2026 |
| Linux | unbound Debian 14 | 1.25.2-1 | [DEBIAN-CVE-2026-14586](https://patchblox.com/security/data/fix/linux/debian-cve-2026-14586.md) | Jul 28, 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 |

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Data as of 2026-11-08T19:12:23Z 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 Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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