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Unbound DNS CVE-2026-14586

| EUVDEUVD-2026-47662 MEDIUM
Reachable Assertion (CWE-617)
2026-07-22 NLnet Labs GHSA-x2gg-pjp4-c6g3
Denial Of Service Unbound Red Hat Suse
5.9
CVSS 3.1 · Vendor: NLnet Labs
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Severity by source

Vendor (NLnet Labs) PRIMARY
5.9 MEDIUM
AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
vuln.today AI
5.9 MEDIUM

Network-reachable via DoQ port (AV:N); triggering requires high concurrency under load (AC:H); no credentials needed (PR:N); server abort is full availability loss (A:H); no confidentiality or integrity impact.

3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
4.0 AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
SUSE
MEDIUM
qualitative
Red Hat
5.9 MEDIUM
qualitative

Primary rating from Vendor (NLnet Labs).

CVSS VectorVendor: NLnet Labs

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

Lifecycle Timeline

2
Patch available
Jul 22, 2026 - 16:18 EUVD
Analysis Generated
Jul 22, 2026 - 13:46 vuln.today

DescriptionCVE.org

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.

AnalysisAI

Denial of service in NLnet Labs Unbound 1.22.0 through 1.25.1 causes server termination when DNS-over-QUIC (DoQ) is enabled and the resolver operates under high concurrency. Unbound incorrectly passes realtime clock values to libngtcp2 where monotonic timestamps are required; under load, the resulting assertion failure in libngtcp2 abruptly kills the Unbound process. No public exploit code exists and no active exploitation has been reported, but the self-termination of a DNS resolver constitutes a severe availability impact for any infrastructure depending on it.

Technical ContextAI

Unbound is a validating, recursive, caching DNS resolver maintained by NLnet Labs. The vulnerable code path involves its optional DNS-over-QUIC transport layer, which relies on libngtcp2 - a C library implementing the QUIC protocol. libngtcp2 requires callers to supply monotonic timestamps (via CLOCK_MONOTONIC) to enforce the invariant that time never goes backward within a QUIC session. Unbound was instead supplying CLOCK_REALTIME values, which can decrease (e.g., due to NTP corrections or clock slew). Under high concurrency, the probability of libngtcp2 observing a non-monotonic timestamp rises enough to trigger a built-in assertion guard (CWE-617: Reachable Assertion), which calls abort() and terminates the process. The affected product is identified in NVD as cpe:2.3:a:nlnet_labs:unbound:*:*:*:*:*:*:*:* covering versions 1.22.0 to 1.25.1.

RemediationAI

Consult the NLnet Labs advisory at https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-14586.txt for the patched release version; a specific fixed version number was not confirmed in the data available at time of analysis. As an immediate compensating control, operators can remove the 'quic-port' directive from Unbound's configuration and restart the service, which disables the DoQ listener entirely and eliminates the vulnerable code path with no impact on standard DNS-over-UDP or DNS-over-TLS operation. Alternatively, operators may recompile Unbound without the '--with-libngtcp2' flag, though this requires a rebuild and redeployment. If DoQ is operationally required, rate-limiting inbound QUIC connections at a network boundary (firewall or load balancer) to reduce concurrency may reduce the probability of triggering the assertion, but this is not a reliable mitigation and should be treated as a temporary measure only.

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7.5 Sep 26

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7.5 Nov 27

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Same weakness CWE-617 – Reachable Assertion

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Same technique Denial Of Service

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CVE-2015-5119 CRITICAL POC
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CVE-2011-2462 CRITICAL POC
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CVE-2011-0611 HIGH POC
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Vendor StatusVendor

SUSE

Severity: Moderate
Product Status
openSUSE Tumbleweed Fixed
SUSE Linux Enterprise Desktop 15 SP7 Not-Affected
SUSE Linux Enterprise High Performance Computing 15 SP7 Not-Affected
SUSE Linux Enterprise Micro 5.5 Not-Affected
SUSE Linux Enterprise Module for Basesystem 15 SP7 Not-Affected

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CVE-2026-14586 vulnerability details – vuln.today
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