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

mediumCVSS 5.9CVE-2026-14586

CSIRTS triage

vendor: null product: nullOther

What: An assertion failure in libngtcp2 can occur under high concurrency in DNS-over-QUIC environments.
Who is affected: Deployments using DNS-over-QUIC are affected.
Urgency: Remediation is medium urgency due to potential service instability.
Action: Update libngtcp2 to the latest version.

AI-assisted analysis generated from the source advisory — verify against the original.

⚡ Watch null

Get an email when a new null advisory drops — max one per day, one-click unsubscribe.

Details

Source: Microsoft Security Response Center (INTL · vendor-psirt · site)
Severity: medium — CVSS 5.9
Published: 2026-07-14
Exploitation: Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-14586

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-145860.27% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 19% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-14586	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

Recent advisories for Assertion in libngtcp2

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

mediumCVE-2026-55991: In NLnet Labs Unbound 1.22.0 up to and including 1.25.1, a remote unauthenticated client can t…nvd · 2026-07-22
mediumCVE-2026-14586: In NLnet Labs Unbound 1.22.0 up to and including 1.25.1, in DNS-over-QUIC environments, with h…nvd · 2026-07-22
mediumCVE-2026-55991: Remote DNS-over-QUIC (DoQ) flow-control assertion failure in libngtcp2msrc · 2026-07-14