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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
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
Which versions are affected by CVE-2026-14586?
How do I fix CVE-2026-14586?
Upgrade to a fixed version.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-14586 being exploited?
There is no known exploitation of CVE-2026-14586 in the wild and no public exploit code.
Sources
Also known as AZL-92967, DEBIAN-CVE-2026-14586, ECHO-e518-e2e7-e89c, GHSA-x2gg-pjp4-c6g3, UBUNTU-CVE-2026-14586.