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

> An assertion failure in libngtcp2 causes Unbound to terminate under high concurrency in DNS-over-QUIC environments, resulting in denial of service.

- **Severity:** Medium 5.9 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 22 Jul 2026
- **Updated:** 22 Jul 2026
- **Also known as:** AZL-92967, DEBIAN-CVE-2026-14586, ECHO-e518-e2e7-e89c, GHSA-x2gg-pjp4-c6g3, UBUNTU-CVE-2026-14586

## What is CVE-2026-14586?

CVE-2026-14586 is a medium-severity denial of service vulnerability in NLnet Labs Unbound, published on 22 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-617 (Reachable Assertion)

## Which versions are affected by CVE-2026-14586?


## How do I fix CVE-2026-14586?

Upgrade to a fixed version.

## Is CVE-2026-14586 being exploited?

There is no known exploitation of CVE-2026-14586 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-14586 and fix it if it is affected.

What it is: CVE-2026-14586 is a medium-severity denial of service vulnerability in NLnet Labs Unbound, published on 22 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-14586 in the wild and no public exploit code.

Affected product: NLnet Labs Unbound. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-14586/ (Markdown: https://insights.sbomify.com/CVE-2026-14586/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-14586
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-14586
- OSV: https://osv.dev/vulnerability/CVE-2026-14586

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-14586/
Summaries are generated and may contain mistakes; the official description above is the record.