CVE intelligence

CVE-2026-81634

Vulnerability intelligence

Published Sep 16, 2026Sources checked Nov 10, 2026

7.5HIGHCVSS out of 10

What this means

Review the available evidence

CVE-2026-81634 and is rated High severity with a CVSS score of 7.5. It is not in the current CISA KEV record we collected. That does not prove exploitation has not occurred.

What to do next

Remediation and response

Ubuntu Security Notices guidance

Vendor revision: Nov 10, 2026

USN-8946-1 fixed vulnerabilities in Unbound in Ubuntu 26.04 LTS, Ubuntu 24.04 LTS, Ubuntu 22.04 LTS, Ubuntu 20.04 LTS, Ubuntu 18.04 LTS, Ubuntu 16.04 LTS, and Ubuntu 14.04 LTS.

Microsoft Security Response Center guidance

Vendor revision: Sep 19, 2026

See the Microsoft Security Update Guide for the update that applies to your product.

Vendor-listed releases

1.26.1-1

CISA KEVNot listedBased on the latest collected catalog

EPSS0.5%Estimated 30-day exploitation probability

Ransomware useNot markedCISA KEV ransomware field

Threat actors0Source-linked actor relationships

Overview

What is CVE-2026-81634?

In NLnet Labs Unbound up to and including 1.26.0, a 255 length query name with a large TCP response can lead to a heap buffer overflow during the RRSet canonicalisation routine. This is caused by missing to add the first owner name into the buffer length check.

A malicious actor operating a malicious name server or tampering with an incoming response to Unbound (canonicalisation happens before DNSSEC validation), can trigger the vulnerability.

Source: NVD